Hypothalamus-Pituitary-Thyroid Axis Quiz
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Hypothalamus-Pituitary-Thyroid Axis Quiz

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Questions and Answers

What initiates the secretion of thyrotrophin releasing hormone (TRH)?

  • Excess release of Thyroid stimulating hormone (TSH)
  • Direct stimulation from the thyroid gland
  • Low levels of T3 and T4 (correct)
  • High levels of T3 and T4

    • Which gland is targeted by thyrotrophin releasing hormone (TRH)?

  • Anterior pituitary gland (correct)
  • Thyroid gland
  • Hypothalamus
  • Posterior pituitary gland

    • What is the final outcome of the hypothalamus-pituitary axis concerning thyroid hormones?

  • Release of T3 and T4 from the thyroid gland (correct)
  • Stimulation of the posterior pituitary gland
  • Inhibition of TRH release
  • Decrease in TSH production

    • Following the release of TSH, which process occurs next?

    <p>Increase in thyroid hormone levels</p> Signup and view all the answers

    Which hormone does the anterior pituitary gland release in response to TRH?

    <p>Thyroid stimulating hormone (TSH)</p> Signup and view all the answers

    What is the primary role of thyroid stimulating hormone (TSH) in the hypothalamus-pituitary axis?

    <p>To stimulate the thyroid gland to release T3 and T4</p> Signup and view all the answers

    What happens when there are high levels of T3 in the bloodstream?

    <p>Inhibition of TSH release from the anterior pituitary</p> Signup and view all the answers

    What triggers the hypothalamus to secrete thyrotrophin releasing hormones (TRH)?

    <p>Low levels of thyroid hormones T3 and T4</p> Signup and view all the answers

    In the context of the hypothalamus-pituitary axis, what does the thyroid gland release in response to TSH?

    <p>Thyroid hormones T3 and T4</p> Signup and view all the answers

    How does the hypothalamus-pituitary axis maintain homeostasis in thyroid hormone levels?

    <p>Through negative feedback mechanisms involving T3</p> Signup and view all the answers

    What is the primary effect of parathyroid hormone (PTH) on the bones?

    <p>It activates osteoclasts to digest the bone matrix.</p> Signup and view all the answers

    How does parathyroid hormone (PTH) influence calcium absorption in the intestines?

    <p>It enhances calcium absorption from dietary sources.</p> Signup and view all the answers

    What role does PTH play in the kidneys regarding vitamin D?

    <p>It activates the promotion of vitamin D synthesis.</p> Signup and view all the answers

    What feedback mechanism inhibits the release of parathyroid hormone (PTH)?

    <p>Rising calcium levels in the bloodstream.</p> Signup and view all the answers

    Which of the following actions is NOT attributed to parathyroid hormone (PTH)?

    <p>Increasing renal Calcium excretion.</p> Signup and view all the answers

    What effect does parathyroid hormone (PTH) have on osteoclasts in the bones?

    <p>It increases their activity, promoting bone matrix digestion.</p> Signup and view all the answers

    How does PTH affect calcium absorption in the intestines?

    <p>It increases calcium absorption from dietary sources.</p> Signup and view all the answers

    What is the effect of rising calcium levels in the blood on PTH secretion?

    <p>It inhibits the release of PTH.</p> Signup and view all the answers

    What role does PTH play in the kidneys regarding vitamin D?

    <p>PTH enhances the promotion of vitamin D which boosts calcium absorption.</p> Signup and view all the answers

    Which action is primarily triggered by hypocalcaemia?

    <p>Stimulation of parathyroid hormone (PTH) release.</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of angiotensinogen to angiotensin I?

    <p>Renin</p> Signup and view all the answers

    What is the main action of aldosterone in the RAAS system?

    <p>Increases sodium ion absorption and subsequently water absorption</p> Signup and view all the answers

    What is the site of conversion from angiotensin I to angiotensin II?

    <p>Lungs by ACE</p> Signup and view all the answers

    How does angiotensin II affect the adrenal cortex?

    <p>Stimulates aldosterone secretion</p> Signup and view all the answers

    What is a consequence of aldosterone action in the body?

    <p>Sodium and water retention</p> Signup and view all the answers

    What physiological effect occurs with elevated levels of angiotensin II?

    <p>Vasoconstriction and increased blood pressure</p> Signup and view all the answers

    Which hormone promotes the retention of sodium in the nephron?

    <p>Aldosterone</p> Signup and view all the answers

    What role does renin play in the RAAS system?

    <p>Converts angiotensinogen to angiotensin I</p> Signup and view all the answers

    What is the primary way cortisol influences protein metabolism?

    <p>Inhibits protein synthesis</p> Signup and view all the answers

    Which process is notably stimulated by cortisol during times of stress?

    <p>Conversion of non-carbohydrate sources into glucose</p> Signup and view all the answers

    Which description best defines the process of lipolysis in relation to cortisol?

    <p>Breaking down stored fats into free fatty acids</p> Signup and view all the answers

    In what way does cortisol assist in energy production during stress responses?

    <p>By providing essential fuel for metabolism</p> Signup and view all the answers

    What is a significant anti-inflammatory action of cortisol in the body?

    <p>Reduces inflammation by suppressing immune responses</p> Signup and view all the answers

    What hormone acts to decrease blood glucose levels following a meal?

    <p>Insulin</p> Signup and view all the answers

    Which mechanism is primarily responsible for the release of glucose into the bloodstream when blood sugar levels are low?

    <p>Glucagon stimulating glycogenolysis</p> Signup and view all the answers

    How does glucagon function when blood glucose levels are elevated?

    <p>Initiates the conversion of glycogen to glucose</p> Signup and view all the answers

    In response to low blood glucose, what is the primary action of the pancreas?

    <p>Release of glucagon</p> Signup and view all the answers

    When blood glucose rises, which substance is primarily responsible for facilitating its storage in the liver?

    <p>Insulin</p> Signup and view all the answers

    What is the primary effect of insulin released by the pancreas?

    <p>Stimulates the liver to store glucose as glycogen</p> Signup and view all the answers

    What physiological response occurs when blood glucose levels are too high?

    <p>The pancreas releases insulin</p> Signup and view all the answers

    What process does glucagon initiate in response to low blood glucose levels?

    <p>Glycogenolysis</p> Signup and view all the answers

    Which hormone is responsible for raising blood glucose levels?

    <p>Glucagon</p> Signup and view all the answers

    How does the body primarily respond to a decrease in blood glucose levels?

    <p>Increase glucagon secretion</p> Signup and view all the answers

    Which receptors are situated on the basolateral surface of parietal cells?

    <p>H2, gastrin, and acetylcholine receptors</p> Signup and view all the answers

    What is the main function of the proton pump in parietal cells?

    <p>To transport hydrogen ions out and potassium ions in</p> Signup and view all the answers

    How is hydrochloric acid produced in the gastric lumen?

    <p>By combining hydrogen ions with chloride ions</p> Signup and view all the answers

    What occurs at the basolateral surface of parietal cells concerning ion exchange?

    <p>Chlorine in, bicarbonate out</p> Signup and view all the answers

    What structure in parietal cells opens directly into the gastric lumen?

    <p>Gastric pit</p> Signup and view all the answers

    Which receptors specifically activate the secretion of gastric acid in parietal cells?

    <p>H2, gastrin, and acetylcholine receptors</p> Signup and view all the answers

    What mechanism primarily facilitates the formation of gastric hydrochloric acid?

    <p>The combination of hydrogen ions with chloride ions</p> Signup and view all the answers

    What kind of ion exchange happens through the basolateral membrane of parietal cells?

    <p>Chloride ions enter while bicarbonate ions exit</p> Signup and view all the answers

    What is the primary action of the proton pump in parietal cells?

    <p>To transport hydrogen ions out and potassium ions in</p> Signup and view all the answers

    What anatomical feature directly opens into the gastric lumen from parietal cells?

    <p>Gastric pit</p> Signup and view all the answers

    What role does the tongue play during the oropharyngeal phase of swallowing?

    <p>The tongue moves food back through the mouth and into the valleculae</p> Signup and view all the answers

    Which action is primarily responsible for the movement of food through the oesophagus?

    <p>Peristaltic action and gravity</p> Signup and view all the answers

    What prevents food from entering the airway during swallowing?

    <p>The epiglottis folds down over the trachea</p> Signup and view all the answers

    Which sphincter must open for food to enter the oesophagus after chewing?

    <p>Upper oesophageal sphincter</p> Signup and view all the answers

    What is required for food to move from the oesophagus into the stomach?

    <p>The lower oesophageal sphincter must open</p> Signup and view all the answers

    What occurs during the oropharyngeal phase of swallowing?

    <p>The tongue moves food back through the mouth and into the valleculae</p> Signup and view all the answers

    Which structure is responsible for keeping food from entering the trachea during swallowing?

    <p>The epiglottis</p> Signup and view all the answers

    What combination of actions aids in the movement of food down the oesophagus during the oesophageal phase?

    <p>Peristaltic action and gravity</p> Signup and view all the answers

    Which sphincter must open to facilitate the passage of food into the oesophagus during swallowing?

    <p>Upper oesophageal sphincter</p> Signup and view all the answers

    What condition is necessary for food to pass from the oesophagus to the stomach?

    <p>The lower oesophageal sphincter must open</p> Signup and view all the answers

    What enzymes are responsible for breaking down starch and glycogen into disaccharides?

    <p>Salivary and pancreatic amylases</p> Signup and view all the answers

    Which brush border enzyme breaks down sucrose into monosaccharides?

    <p>Sucrase</p> Signup and view all the answers

    How do monosaccharides enter the capillaries after digestion?

    <p>Facilitated diffusion</p> Signup and view all the answers

    What happens to glucose once it is absorbed into the bloodstream?

    <p>It is stored as glycogen in the liver or used in the citric acid cycle for energy.</p> Signup and view all the answers

    What are proteins initially digested into?

    <p>Oligopeptides</p> Signup and view all the answers

    How do amino acids enter the cells during absorption?

    <p>Sodium co-transporter</p> Signup and view all the answers

    What enzyme breaks down fat into fatty acids and glycerol?

    <p>Lipase</p> Signup and view all the answers

    What structure helps form micelles during fat digestion?

    <p>Bile salts, phospholipids, and cholesterol</p> Signup and view all the answers

    What is the primary role of micelles in the digestion of fats?

    <p>To be absorbed across the cell membrane and form chylomicrons</p> Signup and view all the answers

    Which pathway do chylomicrons take after their formation?

    <p>Into the basolateral space and then carried by lacteals</p> Signup and view all the answers

    What monosaccharides are produced from the breakdown of sucrose?

    <p>Fructose and glucose</p> Signup and view all the answers

    Which enzyme plays a critical role in the breakdown of lactose?

    <p>Lactase</p> Signup and view all the answers

    Where does the majority of protein digestion occur within the human body?

    <p>Small intestine</p> Signup and view all the answers

    What component of micelles provides a hydrophilic surface, aiding fat digestion?

    <p>Bile salts</p> Signup and view all the answers

    Chylomicrons are primarily composed of which substances?

    <p>Triglycerides, cholesterol, and proteins</p> Signup and view all the answers

    What is the main function of bile salts in fat digestion?

    <p>To emulsify fats for easier lipase action</p> Signup and view all the answers

    Which process allows fatty acids and monoglycerides to enter intestinal cells?

    <p>Simple diffusion</p> Signup and view all the answers

    Which enzyme is responsible for activating trypsinogen in the small intestine?

    <p>Enterokinase</p> Signup and view all the answers

    What role does the chemoreceptor trigger zone (CTZ) play in the process of vomiting?

    <p>It receives signals from the blood and communicates with the vomiting center.</p> Signup and view all the answers

    During vomiting, what occurs to the abdominal muscles?

    <p>They contract forcefully along with the diaphragm.</p> Signup and view all the answers

    Which receptor is notably targeted by anti-sickness medications related to vomiting?

    <p>Serotonin 5HT3 receptor.</p> Signup and view all the answers

    How does the lower oesophageal sphincter behave during the vomiting process?

    <p>It relaxes to facilitate the passage of stomach contents.</p> Signup and view all the answers

    Which mechanism prevents food from entering the airways during vomiting?

    <p>Closure of the glottis.</p> Signup and view all the answers

    What additional receptors are implicated in the vomiting reflex, aside from serotonin receptors?

    <p>Dopamine D2 and histamine receptors.</p> Signup and view all the answers

    What anatomical structure closes to prevent regurgitated material from escaping into the nasal cavity during vomiting?

    <p>The soft palate.</p> Signup and view all the answers

    Which physiological action occurs in the body to assist the vomiting response?

    <p>Contraction of the abdominal muscles.</p> Signup and view all the answers

    What hormone released by the hypothalamus directly stimulates the anterior pituitary gland?

    <p>Gonadotrophin-releasing hormone (GnRH)</p> Signup and view all the answers

    What effect does testosterone have on GnRH release?

    <p>It inhibits GnRH release through negative feedback.</p> Signup and view all the answers

    Which cells are primarily responsible for producing inhibin in the male reproductive system?

    <p>Sertoli cells</p> Signup and view all the answers

    What is the main function of follicle-stimulating hormone (FSH) in males?

    <p>To enhance spermatogenesis.</p> Signup and view all the answers

    What is the primary role of androgen binding protein (ABP) in the male reproductive system?

    <p>To maintain high testosterone levels around spermatogenic cells.</p> Signup and view all the answers

    Which hormone is secreted by Leydig cells in response to LH stimulation?

    <p>Testosterone</p> Signup and view all the answers

    What role does inhibin play in the regulation of the male reproductive system?

    <p>To prevent FSH and GnRH release when sperm count is high.</p> Signup and view all the answers

    What is the main outcome of increased levels of testosterone on the hypothalamus?

    <p>Inhibition of GnRH release.</p> Signup and view all the answers

    What are the outer cells in contact with the basal lamina during spermatogenesis?

    <p>Spermatogonia</p> Signup and view all the answers

    What type of division do spermatogonia undergo until puberty?

    <p>Mitosis</p> Signup and view all the answers

    What is the outcome of mitosis of spermatogonia after puberty?

    <p>Both Type A and Type B daughter cells are produced.</p> Signup and view all the answers

    What happens to Type B daughter cells in spermatogenesis?

    <p>They become primary spermatocytes.</p> Signup and view all the answers

    What is the result of meiosis I in primary spermatocytes?

    <p>Formation of haploid secondary spermatocytes</p> Signup and view all the answers

    What process do secondary spermatocytes undergo to produce spermatids?

    <p>Meiosis II</p> Signup and view all the answers

    What is spermiogenesis?

    <p>The transformation of spermatids into spermatozoa.</p> Signup and view all the answers

    What structure is formed at the end of spermiogenesis?

    <p>Spermatozoa</p> Signup and view all the answers

    What are the outer cells in contact with the basal lamina during spermatogenesis?

    <p>Spermatogonia</p> Signup and view all the answers

    What type of division do spermatogonia undergo until puberty?

    <p>Mitosis</p> Signup and view all the answers

    What happens to Type B daughter cells in spermatogenesis?

    <p>They become primary spermatocytes and eventually form 4 spermatids.</p> Signup and view all the answers

    What is the result of meiosis I in primary spermatocytes?

    <p>Formation of haploid secondary spermatocytes</p> Signup and view all the answers

    What process do secondary spermatocytes undergo to produce spermatids?

    <p>Meiosis II</p> Signup and view all the answers

    What is spermiogenesis?

    <p>The process by which spermatids elongate and become spermatozoa.</p> Signup and view all the answers

    What structure is formed at the end of spermiogenesis?

    <p>Spermatozoa</p> Signup and view all the answers

    What is the primary function of Type A daughter cells after mitosis of spermatogonia?

    <p>They remain as stem cells for future divisions.</p> Signup and view all the answers

    What type of cell is in contact with the basal lamina in the testes?

    <p>Spermatogonia</p> Signup and view all the answers

    Until what stage do spermatogonia divide by mitosis?

    <p>Until puberty</p> Signup and view all the answers

    What type of daughter cells are produced by the mitosis of spermatogonia after puberty?

    <p>Type A and Type B</p> Signup and view all the answers

    What is the role of Type A daughter cells in spermatogenesis?

    <p>They stay in the basal lamina to continue producing more spermatogonia.</p> Signup and view all the answers

    What process do primary spermatocytes undergo to produce haploid secondary spermatocytes?

    <p>Meiosis I</p> Signup and view all the answers

    Which process leads to the production of spermatids from secondary spermatocytes?

    <p>Meiosis II</p> Signup and view all the answers

    What does the process of spermiogenesis produce?

    <p>Spermatozoa</p> Signup and view all the answers

    During spermiogenesis, what significant changes occur to spermatids?

    <p>They elongate, remove cytoplasmic baggage, and develop a tail.</p> Signup and view all the answers

    What is produced during ovulation in the context of oogenesis?

    <p>Secondary oocyte (haploid)</p> Signup and view all the answers

    At what stage of development does the oogonium stop in utero?

    <p>Prophase I</p> Signup and view all the answers

    What process does a primary oocyte undergo at ovulation each month post-puberty?

    <p>Meiosis I</p> Signup and view all the answers

    Where does the secondary oocyte complete meiosis II?

    <p>In the fallopian tube</p> Signup and view all the answers

    What is the result of the completion of meiosis II in the secondary oocyte?

    <p>Formation of a zygote</p> Signup and view all the answers

    What type of cell is the oogonium before undergoing mitosis?

    <p>Diploid (2n)</p> Signup and view all the answers

    What triggers the secondary oocyte to complete meiosis II?

    <p>Fertilization by a sperm cell</p> Signup and view all the answers

    At what stage is oogenesis arrested before ovulation occurs?

    <p>Prophase I</p> Signup and view all the answers

    What type of oocyte is present in a primordial follicle?

    <p>Primary oocyte</p> Signup and view all the answers

    Which structures are present in a primary follicle?

    <p>A primary oocyte, zona pellucida, theca interna &amp; externa, and granulosa cells</p> Signup and view all the answers

    What type of oocyte is found in an early antral (secondary) follicle?

    <p>Primary oocyte</p> Signup and view all the answers

    Which stage of follicular development is associated with the presence of a secondary oocyte?

    <p>Graafian (vesicular) follicle</p> Signup and view all the answers

    What structure is characteristic of the Graafian follicle?

    <p>Antrum filled with follicular fluid, corona radiata, and cumulus oophorus</p> Signup and view all the answers

    What happens to the follicle after ovulation?

    <p>It forms the corpus luteum and secretes progesterone.</p> Signup and view all the answers

    What is the function of the corpus luteum?

    <p>To secrete progesterone for maintaining the uterine lining</p> Signup and view all the answers

    What is the corpus albicans?

    <p>A degenerating corpus luteum</p> Signup and view all the answers

    What occurs to the corpus luteum if the secondary oocyte is not fertilized?

    <p>It transforms into the corpus albicans.</p> Signup and view all the answers

    Which event signifies the conclusion of the follicular phase in the menstrual cycle?

    <p>The occurrence of ovulation.</p> Signup and view all the answers

    What is the primary role of the corpus luteum following ovulation?

    <p>To produce progesterone to maintain pregnancy.</p> Signup and view all the answers

    What might happen if the corpus luteum does not degenerate after ovulation?

    <p>It could maintain elevated hormone levels, preventing menstruation.</p> Signup and view all the answers

    Which hormone is crucial for the surge that triggers ovulation?

    <p>Luteinizing hormone (LH).</p> Signup and view all the answers

    What is the main outcome of the Graafian follicle during ovulation?

    <p>It releases a secondary oocyte.</p> Signup and view all the answers

    What change in hormones marks the beginning of the ovulatory phase?

    <p>A surge in luteinizing hormone (LH).</p> Signup and view all the answers

    Which mechanism contributes to the rupture of the follicular wall during ovulation?

    <p>Enzymatic degradation of follicular proteins.</p> Signup and view all the answers

    What occurs to the remaining follicle after the secondary oocyte has been released?

    <p>It becomes the corpus luteum.</p> Signup and view all the answers

    During which phase of the menstrual cycle does ovulation take place?

    <p>Ovulatory phase.</p> Signup and view all the answers

    What role does the increased volume of follicular fluid play in ovulation?

    <p>It provides mechanical pressure for rupture.</p> Signup and view all the answers

    What does the role of the theca interna include during the ovulation process?

    <p>Contracting to help expel the oocyte.</p> Signup and view all the answers

    What is the typical day of ovulation in a standard 28-day menstrual cycle?

    <p>Day 14/28</p> Signup and view all the answers

    What hormone released by the hypothalamus acts on the anterior pituitary to regulate reproduction in females?

    <p>Gonadotrophin-releasing hormone (GnRH)</p> Signup and view all the answers

    What role does follicle-stimulating hormone (FSH) primarily serve in female reproductive physiology?

    <p>Encourage growth of ovarian follicles</p> Signup and view all the answers

    Which hormone is critical for inducing LH receptor expression in granulosa cells?

    <p>Follicle-stimulating hormone (FSH)</p> Signup and view all the answers

    What is the primary function of luteinizing hormone (LH) during the ovarian cycle?

    <p>Inducing ovulation and stimulating hormone production</p> Signup and view all the answers

    When does the LH surge typically occur in the menstrual cycle?

    <p>Day 14/28</p> Signup and view all the answers

    Which cells are responsible for producing Anti-Mullerian hormone, and what is their role?

    <p>Granulosa cells; inhibit the development of non-dominant follicles</p> Signup and view all the answers

    Which hormone aids in progesterone production by the corpus luteum following ovulation?

    <p>Luteinizing hormone (LH)</p> Signup and view all the answers

    What hormone is produced by the theca cells that promotes estrogen synthesis?

    <p>LH</p> Signup and view all the answers

    What happens to the endometrial lining when the corpus luteum atrophies and fertilisation does not occur?

    <p>It is shed during menstruation.</p> Signup and view all the answers

    Which hormone is crucial for maintaining the corpus luteum when fertilisation occurs?

    <p>Human Chorionic Gonadotropin (hCG)</p> Signup and view all the answers

    Which layer of the endometrium is responsible for shedding during the menstrual phase?

    <p>Stratum functionalis</p> Signup and view all the answers

    What is the main result of a decrease in progesterone levels after the corpus luteum atrophies?

    <p>Menstrual bleeding occurs</p> Signup and view all the answers

    What role does the corpus luteum play during the menstrual cycle if fertilisation does not take place?

    <p>It eventually degenerates, leading to menstruation.</p> Signup and view all the answers

    What is the primary role of the menstrual cycle in reproduction?

    <p>To prepare the endometrium for fertilisation of the ovum</p> Signup and view all the answers

    During which phase is the stratum functionalis shed?

    <p>Menstrual stage</p> Signup and view all the answers

    What characterizes the proliferative stage of the menstrual cycle?

    <p>The stratum functionalis is repaired and proliferated</p> Signup and view all the answers

    Which hormone is critical for the proliferation of the endometrial lining during the proliferative phase?

    <p>Oestrogen</p> Signup and view all the answers

    What event marks the secretory stage of the menstrual cycle?

    <p>Enhanced uterine receptivity and glandular secretions</p> Signup and view all the answers

    What plays a crucial role in the maintenance of the secretory phase?

    <p>Progesterone from the corpus luteum</p> Signup and view all the answers

    What occurs if hCG does not replace LH in supporting the corpus luteum?

    <p>The corpus luteum atrophies</p> Signup and view all the answers

    Which hormone is primarily responsible for initiating ovulation?

    <p>Luteinizing hormone (LH)</p> Signup and view all the answers

    What is hypocalcaemia?

    <p>Low levels of calcium in the body</p> Signup and view all the answers

    Which gland is stimulated to release parathyroid hormone (PTH) during hypocalcaemia?

    <p>Parathyroid gland</p> Signup and view all the answers

    What effect does PTH have on bone tissue?

    <p>It activates osteoclasts to release calcium and phosphate into the blood.</p> Signup and view all the answers

    What do osteoclasts secrete to digest the bone matrix?

    <p>Proteolytic enzymes and hydrogen ions</p> Signup and view all the answers

    What is the first step in bone fracture repair?

    <p>Formation of a hematoma (big blood clot)</p> Signup and view all the answers

    What forms after the hematoma in bone repair?

    <p>Fibrocartilage callus</p> Signup and view all the answers

    What is the purpose of the fibrocartilage callus?

    <p>To fill the fracture area and stabilize it</p> Signup and view all the answers

    Why does bone degradation occur when PTH is released?

    <p>To release calcium into the blood when calcium levels are low</p> Signup and view all the answers

    What condition is characterized by low levels of calcium in the body?

    <p>Hypocalcaemia</p> Signup and view all the answers

    Which hormone is primarily responsible for activating osteoclasts during low calcium levels?

    <p>Parathyroid hormone (PTH)</p> Signup and view all the answers

    What is the role of proteolytic enzymes secreted by osteoclasts?

    <p>To digest the bone matrix</p> Signup and view all the answers

    What occurs immediately after the formation of a hematoma during bone fracture repair?

    <p>Formation of fibrocartilage callus</p> Signup and view all the answers

    What stabilizes the fracture area after the hematoma is formed?

    <p>Fibrocartilage callus</p> Signup and view all the answers

    What is the immediate purpose of bone degradation triggered by PTH when calcium levels are low?

    <p>To release calcium into the blood</p> Signup and view all the answers

    Which correct sequence occurs during bone fracture repair?

    <p>Hematoma → Fibrocartilage callus → Bony callus</p> Signup and view all the answers

    What role do osteoblasts play in response to PTH activity?

    <p>Form new bone matrix</p> Signup and view all the answers

    What is the primary purpose of bone remodeling?

    <p>To maintain homeostasis of ion levels and repair damaged bone</p> Signup and view all the answers

    Which cells are responsible for digesting the bone matrix during bone remodeling?

    <p>Osteoclasts</p> Signup and view all the answers

    What do osteoclasts secrete to break down bone matrix?

    <p>Proteolytic enzymes and hydrogen ions</p> Signup and view all the answers

    What happens to the calcium and phosphate that osteoclasts release?

    <p>They are phagocytosed and released into the bloodstream.</p> Signup and view all the answers

    What do osteoblasts secrete during bone formation?

    <p>Osteoid, which undergoes mineralisation</p> Signup and view all the answers

    What is osteoid, and what happens to it after secretion?

    <p>A collagen-rich substance; it undergoes mineralisation to form new bone tissue.</p> Signup and view all the answers

    How do osteoclasts contribute to calcium homeostasis?

    <p>By breaking down bone matrix and releasing calcium into the bloodstream.</p> Signup and view all the answers

    What role do osteoblasts play in the remodeling cycle?

    <p>They are involved in the formation of new bone tissue.</p> Signup and view all the answers

    What signifies the start of secondary ossification in bones?

    <p>The emergence of secondary ossification sites in the epiphyses</p> Signup and view all the answers

    Which structure remains as cartilage even after most of the bone has ossified?

    <p>The epiphyseal plates and articular cartilage</p> Signup and view all the answers

    What is transported into the calcified cartilage by the periosteal bud during ossification?

    <p>Blood vessels, nerves, red marrow cells, and osteoclasts</p> Signup and view all the answers

    What characterizes the calcification process during endochondral ossification?

    <p>Hardening of the cartilage matrix</p> Signup and view all the answers

    What is formed as a result of hypertrophy of chondrocytes during endochondral ossification?

    <p>Poor circulation around the cartilage</p> Signup and view all the answers

    What is the primary role of osteoblasts during primary ossification in endochondral ossification?

    <p>They secrete osteoid to create the bone collar.</p> Signup and view all the answers

    What occurs immediately following the formation of the bone collar during endochondral ossification?

    <p>Cartilage begins to ossify.</p> Signup and view all the answers

    What is the function of the periosteal bud in the ossification process?

    <p>It infiltrates calcified cartilage to form spongy bone.</p> Signup and view all the answers

    Which of the following processes occurs as the diaphysis extends during endochondral ossification?

    <p>The medullary cavity expands.</p> Signup and view all the answers

    Where are secondary ossification centers usually located during endochondral ossification?

    <p>In the epiphyses of long bones.</p> Signup and view all the answers

    Which structure remains as cartilage after the primary ossification process is completed?

    <p>The epiphyseal plates and articular cartilage.</p> Signup and view all the answers

    What is the first notable structure formed during endochondral ossification?

    <p>The bone collar around the diaphysis.</p> Signup and view all the answers

    Which step directly follows the calcification of cartilage in the primary ossification process?

    <p>Invasion of blood vessels through the periosteal bud.</p> Signup and view all the answers

    What is the relationship between insulin and osteocalcin?

    <p>Insulin activates osteocalcin, which in turn promotes insulin production.</p> Signup and view all the answers

    Which effect does osteocalcin have on insulin production?

    <p>It enhances the production of insulin by targeting pancreatic beta cells.</p> Signup and view all the answers

    What is a primary function of FGF23 in relation to mineral metabolism?

    <p>It regulates phosphate levels by controlling reabsorption in the kidneys.</p> Signup and view all the answers

    Which statement about the actions of osteocalcin is incorrect?

    <p>Osteocalcin promotes the release of glucagon in response to low blood sugar.</p> Signup and view all the answers

    How does FGF23 influence calcium levels in the body?

    <p>It decreases renal calcium retention by increasing phosphate levels.</p> Signup and view all the answers

    What hormones do osteoblasts secrete as part of their endocrine function?

    <p>Osteocalcin and FGF23</p> Signup and view all the answers

    What is the target of osteocalcin, and what is its effect?

    <p>Pancreatic beta cells; it stimulates cell division and insulin production for glucose uptake.</p> Signup and view all the answers

    How does insulin interact with osteocalcin in bone?

    <p>It activates osteocalcin, forming a two-way synergistic mechanism.</p> Signup and view all the answers

    What condition is associated with reduced osteocalcin levels?

    <p>Type 2 diabetes</p> Signup and view all the answers

    What does osteocalcin trigger the release of from adipocytes?

    <p>Adiponectin, which restricts fat storage</p> Signup and view all the answers

    What is the function of FGF23 secreted by osteoblasts?

    <p>It regulates phosphate reabsorption in the kidneys.</p> Signup and view all the answers

    How does adiponectin, released due to osteocalcin, affect the body?

    <p>It restricts fat storage and improves insulin sensitivity.</p> Signup and view all the answers

    What kind of feedback mechanism exists between insulin and osteocalcin?

    <p>A bidirectional feedback system enhancing both insulin and osteocalcin effects.</p> Signup and view all the answers

    What is required for myosin to enter its cocked state?

    <p>Hydrolysis of ATP by myosin</p> Signup and view all the answers

    What happens to calcium ions after an action potential ceases?

    <p>They are pumped back into the sarcoplasmic reticulum</p> Signup and view all the answers

    Why do cross bridges not form when calcium is returned to the sarcoplasmic reticulum?

    <p>Tropomyosin moves back over the myosin binding sites on actin</p> Signup and view all the answers

    What result does the hydrolysis of ATP by myosin lead to?

    <p>The release of ADP and inorganic phosphate</p> Signup and view all the answers

    Which process primarily facilitates muscle relaxation?

    <p>Active transport of calcium back into the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the initial event that triggers excitation-contraction coupling in muscle cells?

    <p>Neural stimulation causing a wave of depolarisation across the sarcolemma</p> Signup and view all the answers

    Which structure is primarily responsible for releasing calcium into the cytoplasm during muscle contraction?

    <p>Sarcoplasmic reticulum (SR)</p> Signup and view all the answers

    What does calcium bind to in order to initiate muscle contraction?

    <p>Troponin</p> Signup and view all the answers

    What occurs when calcium binds to troponin during muscle contraction?

    <p>Troponin changes shape and moves tropomyosin, exposing myosin binding sites on actin</p> Signup and view all the answers

    What is formed when myosin binds to actin during the contraction process?

    <p>Cross bridges</p> Signup and view all the answers

    What is the consequence of the power stroke during muscle contraction?

    <p>Pulling of the actin filament and shortening of the sarcomere</p> Signup and view all the answers

    What happens immediately after ADP and inorganic phosphate are released during muscle contraction?

    <p>A new ATP molecule binds to the myosin head, causing cross bridge detachment</p> Signup and view all the answers

    During muscle contraction, what structural change occurs as a result of myosin binding to actin?

    <p>Cross bridges are formed</p> Signup and view all the answers

    What is the consequence of synovial fluid leaking into cracks in the bone in osteoarthritis?

    <p>It exacerbates joint damage and may form cysts.</p> Signup and view all the answers

    What triggers the inflammation and pain associated with osteoarthritis?

    <p>Deformation altering biomechanical forces within the joint.</p> Signup and view all the answers

    Which statement best characterizes the progression of osteoarthritis?

    <p>Gradual degeneration of cartilage leading to mechanical wear and joint disruption.</p> Signup and view all the answers

    Which of the following effects is directly linked to the accumulation of synovial fluid due to osteoarthritis?

    <p>Increased risk of developing bone spurs.</p> Signup and view all the answers

    In the context of osteoarthritis, what role does the mechanical wear on cartilage play?

    <p>It contributes to pain and further joint damage.</p> Signup and view all the answers

    What happens to the quality of cartilage in osteoarthritis?

    <p>It becomes more fragile and prone to mechanical wear.</p> Signup and view all the answers

    What is the consequence of synovial fluid leaking into cracks in the bone in osteoarthritis?

    <p>It can lead to the formation of cysts or exacerbate joint damage.</p> Signup and view all the answers

    What are the bony nodules that form in osteoarthritis called?

    <p>Osteophytes</p> Signup and view all the answers

    How do osteophytes affect the joint in osteoarthritis?

    <p>They alter biomechanical forces, causing inflammation and pain.</p> Signup and view all the answers

    What is a common consequence of cartilage degradation in osteoarthritis?

    <p>Mechanical wear and cracking of the underlying bone</p> Signup and view all the answers

    What is a major symptom caused by the changes in joint structure due to osteoarthritis?

    <p>Stiffness, inflammation, and pain in the joint</p> Signup and view all the answers

    What role do osteophytes play in the progression of osteoarthritis?

    <p>They contribute to joint deformation and limit movement.</p> Signup and view all the answers

    What can result from the changes in cartilage due to osteoarthritis?

    <p>Progressive degeneration and loss of joint function.</p> Signup and view all the answers

    Which characteristics do muscles exhibit when they can be stretched and then return to their original shape?

    <p>Extensibility and elasticity</p> Signup and view all the answers

    What is the significance of the elasticity characteristic in muscles?

    <p>It enables muscles to return to their resting length after being stretched.</p> Signup and view all the answers

    Which of the following is considered a characteristic that muscle tissue does not possess?

    <p>Rigidity</p> Signup and view all the answers

    Which pair of muscle characteristics is essential for proper muscle functioning during physical activity?

    <p>Elasticity and contractility</p> Signup and view all the answers

    What might happen if a muscle lacks elasticity?

    <p>It would lose its ability to adapt to stretching.</p> Signup and view all the answers

    What characteristic of muscle allows it to respond to internal or external stimuli?

    <p>Excitability</p> Signup and view all the answers

    Which of these muscle characteristics is essential for a muscle to maintain its shape after being stretched?

    <p>Elasticity</p> Signup and view all the answers

    Which characteristic defines the capability of muscle fibers to shorten in response to stimulation?

    <p>Contractility</p> Signup and view all the answers

    What does the term extensibility refer to in muscle tissue?

    <p>The muscle's ability to stretch beyond its resting length</p> Signup and view all the answers

    Which muscle characteristic is primarily responsible for a muscle's ability to develop tension and support postural stability?

    <p>Contractility</p> Signup and view all the answers

    What is the function of contractility in muscle fibers during physical activities?

    <p>Muscle fibers shorten to create force</p> Signup and view all the answers

    Which characteristic describes a muscle's capacity to stretch beyond its resting length without injury?

    <p>Extensibility</p> Signup and view all the answers

    What best describes how muscle fibers react to a neurotransmitter?

    <p>They exhibit excitability by contracting or responding</p> Signup and view all the answers

    What component does the tubuloglomerular feedback mechanism primarily monitor to regulate GFR?

    <p>Concentration of salt in the tubule fluid at the macula densa</p> Signup and view all the answers

    Which function is performed by the macula densa?

    <p>To monitor the concentration of salt in the tubule fluid</p> Signup and view all the answers

    What is an outcome of having a high GFR?

    <p>The tubules may not have enough time to reabsorb necessary substances</p> Signup and view all the answers

    What physiological change triggers the myogenic response in the kidney?

    <p>Alterations in blood pressure within the afferent arteriole</p> Signup and view all the answers

    What will happen to kidney function if the concentration of salt is low in the tubule fluid?

    <p>Decrease in urine output</p> Signup and view all the answers

    What is the primary role of hydrostatic pressure in the kidneys?

    <p>To push fluids and solutes through the filtration membrane</p> Signup and view all the answers

    Which mechanism assists in maintaining a consistent glomerular filtration rate (GFR) despite fluctuating blood pressure?

    <p>Myogenic response</p> Signup and view all the answers

    Which of these options describes intrinsic control of GFR?

    <p>It regulates GFR based on internal kidney conditions.</p> Signup and view all the answers

    What happens to the resistance of afferent arterioles when systemic blood pressure decreases?

    <p>They relax, increasing blood flow to the glomerulus.</p> Signup and view all the answers

    What is the myogenic feedback mechanism crucial for?

    <p>Adjusting smooth muscle contraction in response to blood pressure changes.</p> Signup and view all the answers

    What is the likely consequence of maintaining a GFR that is too high?

    <p>Risk of losing essential nutrients in urine</p> Signup and view all the answers

    Which statement accurately describes the significance of GFR regulation?

    <p>It is critical for maintaining electrolyte balance and overall homeostasis.</p> Signup and view all the answers

    How does increased blood flow affect the glomerular filtration rate?

    <p>It causes an increase in GFR.</p> Signup and view all the answers

    What regulates the glomerular filtration rate (GFR) via tubuloglomerular feedback?

    <p>Concentration of salt in the tubule fluid at the macula densa</p> Signup and view all the answers

    What essential function does the macula densa serve in relation to kidney function?

    <p>To monitor the concentration of salt in the tubule fluid.</p> Signup and view all the answers

    What consequence occurs when the GFR is elevated excessively?

    <p>Tubules may fail to reabsorb essential substances adequately.</p> Signup and view all the answers

    What specifically triggers the myogenic response in kidney regulation?

    <p>Changes in blood pressure within the afferent arteriole</p> Signup and view all the answers

    Which of the following mechanisms does NOT directly influence glomerular filtration rate (GFR)?

    <p>Alterations in the volume of the renal medulla</p> Signup and view all the answers

    What defines the glomerular filtration rate (GFR)?

    <p>The volume of filtrate formed per minute in the kidneys</p> Signup and view all the answers

    Which physiological mechanism primarily influences glomerular filtration in response to changes in blood pressure?

    <p>Myogenic response of vascular smooth muscle</p> Signup and view all the answers

    What role does hydrostatic pressure play in glomerular filtration?

    <p>It forces fluids and solutes through the filtration membrane</p> Signup and view all the answers

    What is the primary effect of changes in systemic blood pressure on GFR regulation?

    <p>Alters the resistance of afferent and efferent arterioles</p> Signup and view all the answers

    What is intrinsic control in kidney function primarily responsible for?

    <p>Maintaining consistent GFR despite external changes</p> Signup and view all the answers

    How do kidneys maintain a consistent GFR even when blood pressure changes significantly?

    <p>By adjusting resistance to blood flow within the renal vasculature</p> Signup and view all the answers

    What characterizes the myogenic feedback mechanism in renal physiology?

    <p>It reacts to blood pressure variations by adjusting smooth muscle response</p> Signup and view all the answers

    What could likely happen if GFR is insufficiently regulated?

    <p>Variable urine output resulting in dehydration or volume overload</p> Signup and view all the answers

    What is the main effect of aldosterone on sodium in the kidneys?

    <p>It increases sodium and water reabsorption, which increases blood volume.</p> Signup and view all the answers

    Where does the majority of tubular reabsorption occur in the nephron?

    <p>Proximal convoluted tubule (PCT)</p> Signup and view all the answers

    Which routes can tubular reabsorption in the nephron utilize?

    <p>Either transcellular or paracellular route</p> Signup and view all the answers

    How does vasoconstriction affect systemic blood pressure?

    <p>It increases blood pressure by reducing vessel diameter.</p> Signup and view all the answers

    Which part of the nephron is primarily responsible for reabsorbing materials after initial filtration?

    <p>Proximal convoluted tubule (PCT)</p> Signup and view all the answers

    What is the primary purpose of extrinsic controls in the regulation of GFR?

    <p>To maintain systemic blood pressure</p> Signup and view all the answers

    How does the sympathetic nervous system affect renal function during a decrease in systemic blood pressure?

    <p>It releases norepinephrine, causing afferent arterioles to constrict and decrease GFR.</p> Signup and view all the answers

    What mechanism triggers the release of norepinephrine by the sympathetic nervous system in response to low blood pressure?

    <p>Baroreceptor reflex</p> Signup and view all the answers

    What is the effect of afferent arterioles constriction on GFR?

    <p>It decreases GFR.</p> Signup and view all the answers

    Which hormone is released by granular cells of the afferent arteriole when blood pressure falls?

    <p>Renin</p> Signup and view all the answers

    In the renin-angiotensin-aldosterone mechanism, what does renin do?

    <p>Converts angiotensinogen to angiotensin I</p> Signup and view all the answers

    What enzyme is responsible for converting angiotensin I to angiotensin II?

    <p>ACE (Angiotensin-converting enzyme)</p> Signup and view all the answers

    What physiological effect does angiotensin II have on blood vessels?

    <p>It causes vasoconstriction, increasing systemic blood pressure.</p> Signup and view all the answers

    What mechanism directly links the rate of glomerular filtration to the concentration of salt in the tubule fluid?

    <p>Tubuloglomerular feedback</p> Signup and view all the answers

    What would be the expected renal response if systemic blood pressure decreases?

    <p>Renin is released to activate the renin-angiotensin-aldosterone mechanism</p> Signup and view all the answers

    Which process is primarily responsible for reabsorbing most of the filtrate back into the bloodstream?

    <p>Tubular reabsorption</p> Signup and view all the answers

    What is the primary action of aldosterone within the kidneys?

    <p>To increase sodium and water reabsorption, raising blood volume</p> Signup and view all the answers

    Which mechanism is responsible for changing the glomerular filtration rate in response to varying sodium concentrations in the tubule fluid?

    <p>Tubuloglomerular feedback</p> Signup and view all the answers

    What role does the baroreceptor reflex play in regulating glomerular filtration rate (GFR)?

    <p>It triggers afferent arteriole constriction to lower GFR and help restore blood pressure.</p> Signup and view all the answers

    What happens when angiotensin II stimulates the adrenal cortex?

    <p>It secretes aldosterone.</p> Signup and view all the answers

    Which statement best describes how angiotensin II affects systemic blood pressure?

    <p>It causes vasoconstriction of systemic arterioles, increasing blood pressure.</p> Signup and view all the answers

    What occurs if systemic blood pressure drops significantly?

    <p>Sympathetic stimulation causes the release of norepinephrine, leading to afferent arteriole constriction.</p> Signup and view all the answers

    How does angiotensin II contribute to increasing blood volume?

    <p>By stimulating aldosterone to promote sodium and water reabsorption.</p> Signup and view all the answers

    What triggers the release of renin from the granular cells of the afferent arteriole?

    <p>Decreased systemic blood pressure.</p> Signup and view all the answers

    What physiological response occurs when the body experiences low sodium levels?

    <p>Increased aldosterone secretion to retain sodium.</p> Signup and view all the answers

    How does sympathetic stimulation affect renal blood flow during stress?

    <p>It causes vasoconstriction of the afferent arterioles.</p> Signup and view all the answers

    What initiates the first step in the transcellular route of reabsorption?

    <p>Transport across the apical membrane</p> Signup and view all the answers

    In the nephron, which segment is responsible for nearly all glucose and amino acid reclamation?

    <p>Proximal convoluted tubule (PCT)</p> Signup and view all the answers

    Which ions are primarily reabsorbed in the ascending limb of the loop of Henle?

    <p>Sodium, chloride, potassium, magnesium, and calcium</p> Signup and view all the answers

    What is the main function of the basolateral membrane during the reabsorption process?

    <p>Facilitates transport from the cytosol to the interstitial fluid</p> Signup and view all the answers

    What percentage of sodium ions and water are reabsorbed in the proximal convoluted tubule (PCT)?

    <p>65%</p> Signup and view all the answers

    Which compound is primarily reabsorbed in the collecting duct?

    <p>Sodium, chloride, potassium, bicarbonate, water, and urea</p> Signup and view all the answers

    Which of the following best describes the paracellular route of reabsorption?

    <p>Movement through tight junctions to enter the interstitium</p> Signup and view all the answers

    What is the main substance reabsorbed in the descending limb of the loop of Henle?

    <p>Water</p> Signup and view all the answers

    How does tubular secretion help in managing blood pH levels?

    <p>It generates more bicarbonate when blood pH becomes acidic.</p> Signup and view all the answers

    What is the fate of excess potassium ions in the kidneys?

    <p>They are actively secreted under the influence of aldosterone.</p> Signup and view all the answers

    What effect does aldosterone have on potassium regulation?

    <p>It leads to increased potassium secretion in specific renal segments.</p> Signup and view all the answers

    What is the primary action of antidiuretic hormone (ADH) in the kidneys?

    <p>It enhances the permeability of collecting duct cells to water.</p> Signup and view all the answers

    In what way does tubular secretion contribute to renal function?

    <p>It clears metabolic waste from the blood by secretion.</p> Signup and view all the answers

    What is the primary function of anti-diuretic hormone (ADH) in the kidneys?

    <p>It inhibits diuresis and increases water reabsorption.</p> Signup and view all the answers

    What physiological condition is most likely to trigger the release of aldosterone?

    <p>Decrease in blood pressure or volume</p> Signup and view all the answers

    In what way does aldosterone influence sodium and water balance in the kidneys?

    <p>It increases sodium reabsorption, resulting in more water retention.</p> Signup and view all the answers

    Which hormone has a counter-regulatory effect against aldosterone in the body?

    <p>Atrial natriuretic peptide (ANP)</p> Signup and view all the answers

    What is the main objective of tubular secretion in renal physiology?

    <p>To eliminate waste from the blood into the urine.</p> Signup and view all the answers

    Which of the following accurately describes an important role of tubular secretion?

    <p>Eliminating drugs and metabolites bound to plasma proteins.</p> Signup and view all the answers

    Which factor primarily regulates the secretion of aldosterone?

    <p>Decreased blood volume or pressure and high potassium levels</p> Signup and view all the answers

    What happens to water reabsorption in the collecting duct when ADH levels are low?

    <p>Water reabsorption decreases significantly.</p> Signup and view all the answers

    Which role does urea play in forming the medullary gradient in the kidneys?

    <p>Urea enters the filtrate in the ascending limb via diffusion and recycles back into the interstitial fluid.</p> Signup and view all the answers

    What is the main effect of ADH on urea transport in the kidneys?

    <p>It enhances urea transport out of the collecting duct into the interstitial fluid.</p> Signup and view all the answers

    What occurs to urea at the end of the collecting duct in the renal medulla?

    <p>It diffuses into the interstitial fluid and recycles back into the ascending limb.</p> Signup and view all the answers

    Which mechanism is primarily responsible for concentrating urine within the nephron?

    <p>Countercurrent mechanism involving the loop of Henle and vasa recta.</p> Signup and view all the answers

    How does urea influence water reabsorption in the nephron?

    <p>By increasing the water permeability in the collecting duct when ADH is present.</p> Signup and view all the answers

    What is the primary function of the counter current multiplier in the kidney?

    <p>To create an osmotic gradient that concentrates urine</p> Signup and view all the answers

    Which segment of the nephron is critical for the counter current multiplier mechanism?

    <p>Loop of Henle</p> Signup and view all the answers

    As NaCl is reabsorbed from the ascending limb of the loop of Henle, what effect does this have on the descending limb?

    <p>More water leaves the descending limb</p> Signup and view all the answers

    What mechanism does the ascending limb use to contribute to the concentration of the interstitial fluid?

    <p>It uses concentrated filtrate from the descending limb to increase NaCl transport</p> Signup and view all the answers

    Which statement best describes the function of the vasa recta in maintaining the osmotic gradient?

    <p>To preserve the medullary gradient and remove reabsorbed water</p> Signup and view all the answers

    What is the role of the vasa recta in relation to the salts within the renal medulla?

    <p>To prevent rapid removal of salts from the interstitial space</p> Signup and view all the answers

    What effect does increased reabsorption of NaCl in the ascending limb have on the osmotic balance within the nephron?

    <p>It allows more water reabsorption in the descending limb</p> Signup and view all the answers

    How does the counter current mechanism affect urine concentration levels?

    <p>It enables the production of highly concentrated urine</p> Signup and view all the answers

    What is the innermost layer of a blood vessel called?

    <p>Tunica interna (intima)</p> Signup and view all the answers

    What is the function of smooth muscle cells in the tunica media?

    <p>Regulates the diameter of the lumen</p> Signup and view all the answers

    What is the main function of the tunica externa?

    <p>Anchors the vessel to surrounding tissues</p> Signup and view all the answers

    Which of the following describes the composition of the tunica media?

    <p>Smooth muscle cells and external elastic lamina</p> Signup and view all the answers

    Which layer of the blood vessel primarily contains nerves and the vasa vasorum?

    <p>Tunica externa (adventitia)</p> Signup and view all the answers

    What happens to osmolality of the extracellular fluid (ECF) when a person is overhydrated?

    <p>It decreases.</p> Signup and view all the answers

    What is the result of a decrease in ADH release due to overhydration?

    <p>Decreased water reabsorption in the collecting duct</p> Signup and view all the answers

    What type of urine is produced when a person is overhydrated?

    <p>Large volume of dilute urine</p> Signup and view all the answers

    What happens to ADH release when a person is dehydrated?

    <p>It increases.</p> Signup and view all the answers

    Which type of urine is produced during dehydration?

    <p>Small volume of concentrated urine</p> Signup and view all the answers

    What is the function of diuretics?

    <p>Enhance urinary output</p> Signup and view all the answers

    Where do loop diuretics, such as furosemide, act in the nephron?

    <p>Ascending limb of the loop of Henle</p> Signup and view all the answers

    What is the action of potassium-sparing diuretics like eplerenone?

    <p>Block the action of aldosterone</p> Signup and view all the answers

    What best describes the process of bulk flow in the body?

    <p>It regulates the volumes of blood and interstitial fluid.</p> Signup and view all the answers

    How does filtration differ from reabsorption in terms of direction of movement?

    <p>Filtration moves substances from capillaries into interstitial fluid, while reabsorption moves substances from interstitial fluid into capillaries.</p> Signup and view all the answers

    Which statement about the nature of bulk flow is correct?

    <p>It is a passive process based on a pressure gradient.</p> Signup and view all the answers

    What is NOT a characteristic of the process of filtration in bulk flow?

    <p>It actively requires cellular energy to function.</p> Signup and view all the answers

    Which of the following best explains why bulk flow is essential in the human body?

    <p>It is critical for maintaining homeostasis in fluid compartments.</p> Signup and view all the answers

    What is the primary function of capillary exchange?

    <p>To move substances between blood and interstitial fluid</p> Signup and view all the answers

    What is the main process through which substances move down their concentration gradient?

    <p>Diffusion</p> Signup and view all the answers

    Which structures facilitate the passage of water-soluble substances like glucose and ions during capillary exchange?

    <p>Intracellular clefts and fenestrations</p> Signup and view all the answers

    What type of substances can pass through endothelial cells in capillaries?

    <p>Lipid-soluble substances like oxygen and carbon dioxide</p> Signup and view all the answers

    Why can't diffusion occur at the blood-brain barrier (BBB)?

    <p>The endothelial cells form tight junctions that restrict diffusion</p> Signup and view all the answers

    What is transcytosis?

    <p>A process where materials are enclosed in vesicles, enter endothelial cells by endocytosis, and exit by exocytosis</p> Signup and view all the answers

    Which type of molecules are commonly transported via transcytosis?

    <p>Large proteins and hormones</p> Signup and view all the answers

    What characterizes bulk flow in capillary exchange?

    <p>It occurs due to hydrostatic and osmotic pressure gradients</p> Signup and view all the answers

    How does blood flow from the abdominal veins to the thoracic veins during inhalation?

    <p>Because of the pressure gradient created by decreased thoracic pressure and increased abdominal pressure</p> Signup and view all the answers

    What structure prevents the backflow of blood during exhalation in the respiratory pump mechanism?

    <p>Valves in the veins</p> Signup and view all the answers

    What role do valves play in relation to the skeletal muscle pump?

    <p>Valves help direct blood flow towards the heart and prevent backflow during muscle contraction and relaxation</p> Signup and view all the answers

    What occurs to abdominal pressure during inhalation?

    <p>Abdominal pressure decreases, leading to blood flow to the thorax</p> Signup and view all the answers

    Which statement accurately describes the effect of thoracic pressure during inhalation?

    <p>Thoracic pressure decreases, aiding in venous return</p> Signup and view all the answers

    What is the primary function of venous return in the circulatory system?

    <p>To ensure the volume of blood returning to the heart from systemic circulation</p> Signup and view all the answers

    How does the skeletal muscle pump enhance venous return?

    <p>By creating a mechanical compression of veins during muscle contraction</p> Signup and view all the answers

    What occurs during the relaxation phase of the skeletal muscle pump?

    <p>Pressure in the veins decreases, allowing for refilling.</p> Signup and view all the answers

    Which of the following statements best describes the respiratory pump?

    <p>It decreases thoracic cavity pressure during inhalation, aiding venous return.</p> Signup and view all the answers

    During inhalation, what specific pressure changes occur in the thoracic and abdominal cavities?

    <p>Thoracic pressure decreases while abdominal pressure increases.</p> Signup and view all the answers

    What happens to blood flow when the skeletal muscle contracts?

    <p>The proximal valve opens while the distal valve closes, directing blood towards the heart.</p> Signup and view all the answers

    What is the effect of skeletal muscle contraction on venous valves?

    <p>Opens the proximal valve while the distal valve closes to aid forward flow.</p> Signup and view all the answers

    What role does the high pressure play during muscle relaxation in the skeletal muscle pump?

    <p>Allows the distal valve to open to receive blood from the lower limbs.</p> Signup and view all the answers

    What is the primary function of the cardiovascular center?

    <p>To regulate blood pressure and blood flow</p> Signup and view all the answers

    Which higher brain regions provide nerve impulses to the cardiovascular center?

    <p>Cerebral cortex, limbic system, and hypothalamus</p> Signup and view all the answers

    What type of sensory receptor is responsible for monitoring blood pressure?

    <p>Baroreceptors</p> Signup and view all the answers

    Which receptor type is responsible for monitoring blood acidity and CO2 levels?

    <p>Chemoreceptors</p> Signup and view all the answers

    Which type of nerves sends inhibitory signals from the cardiovascular center to the heart?

    <p>Vagus nerves</p> Signup and view all the answers

    What effect do parasympathetic signals from the cardiovascular center have on heart activity?

    <p>Decrease heart rate</p> Signup and view all the answers

    Which nerves are associated with increasing heart rate and contractility?

    <p>Cardiac accelerator nerves (sympathetic)</p> Signup and view all the answers

    What type of nerve output from the cardiovascular center is responsible for vasoconstriction?

    <p>Vasomotor nerves (sympathetic)</p> Signup and view all the answers

    What response occurs when baroreceptors detect a decrease in blood pressure?

    <p>The CVC sends signals to increase heart rate and vasoconstriction.</p> Signup and view all the answers

    What is the primary action of the aortic reflex when systemic blood pressure increases?

    <p>It activates parasympathetic stimulation via the vagus nerve to lower blood pressure.</p> Signup and view all the answers

    When blood pressure drops, which mechanism is NOT triggered?

    <p>The body increases its secretion of hormones to lower heart rate.</p> Signup and view all the answers

    Which of the following statements accurately describes a function of baroreceptors?

    <p>They detect changes in blood pressure and help regulate heart rate and vascular resistance.</p> Signup and view all the answers

    What is the main function of baroreceptors in the regulation of blood pressure?

    <p>To monitor changes in pressure and stretch in the walls of blood vessels</p> Signup and view all the answers

    Where are baroreceptors primarily located?

    <p>In large arteries such as the carotid sinus and aortic arch</p> Signup and view all the answers

    Which physiological effect is associated with an increased activation of the sympathetic nervous system during low blood pressure?

    <p>Increased heart rate and enhanced blood vessel constriction.</p> Signup and view all the answers

    Which nerve transmits impulses from the carotid sinus to the cardiovascular center?

    <p>Glossopharyngeal nerve (IX)</p> Signup and view all the answers

    What triggers the carotid sinus reflex?

    <p>Blood pressure stretching the carotid sinus</p> Signup and view all the answers

    How do impulses from the aortic reflex reach the cardiovascular center?

    <p>Through the vagus nerve (X)</p> Signup and view all the answers

    What is the main role of the aortic reflex?

    <p>To regulate systemic blood pressure</p> Signup and view all the answers

    Which reflex primarily helps in maintaining blood flow to the brain?

    <p>Carotid sinus reflex</p> Signup and view all the answers

    Where is the carotid sinus located?

    <p>In the left and right carotid arteries</p> Signup and view all the answers

    What role do chemoreceptors have regarding blood composition?

    <p>They assess O2, H+, and CO2 concentration levels.</p> Signup and view all the answers

    What physiological responses are triggered when chemoreceptors identify high CO2 levels?

    <p>They enhance sympathetic stimulation leading to increased vasoconstriction.</p> Signup and view all the answers

    Which outcome is a direct result of sympathetic stimulation triggered by chemoreceptors?

    <p>Enhanced heart rate and elevated blood pressure.</p> Signup and view all the answers

    How does vasodilation affect systemic blood pressure?

    <p>It causes a significant decrease in blood pressure.</p> Signup and view all the answers

    What condition activates chemoreceptors to send signals for sympathetic response?

    <p>Reduced oxygen and increased CO2 or hydrogen ion concentrations.</p> Signup and view all the answers

    What happens to baroreceptors when blood pressure decreases?

    <p>They become less stretched and send fewer impulses to the CVC.</p> Signup and view all the answers

    How does the cardiovascular center respond when there is a decrease in blood pressure?

    <p>It decreases parasympathetic stimulation and increases sympathetic activity, raising heart rate and cardiac output.</p> Signup and view all the answers

    What physiological change occurs as a result of increased sympathetic activity when blood pressure is low?

    <p>Increased vascular resistance and cardiac output</p> Signup and view all the answers

    What happens when baroreceptors detect an increase in blood pressure?

    <p>They send more impulses to the CVC, stimulating parasympathetic activity.</p> Signup and view all the answers

    How does increased parasympathetic stimulation affect the heart rate and blood pressure?

    <p>It lowers heart rate, cardiac output, and promotes vasodilation, reducing blood pressure.</p> Signup and view all the answers

    Where are chemoreceptors that control blood pressure located?

    <p>In the carotid bodies and aortic bodies near the baroreceptors</p> Signup and view all the answers

    What consequence does a decrease in parasympathetic activity have on heart function?

    <p>It leads to an increase in heart rate and possibly elevated blood pressure.</p> Signup and view all the answers

    What type of changes do chemoreceptors primarily monitor in the blood?

    <p>Chemical composition, specifically O2, H+, and CO2 levels</p> Signup and view all the answers

    Which physiological response occurs when chemoreceptors detect elevated CO2 levels?

    <p>Increased sympathetic stimulation resulting in vasoconstriction</p> Signup and view all the answers

    Which of the following effects does sympathetic stimulation from chemoreceptor impulses NOT produce?

    <p>Vasodilation of peripheral blood vessels</p> Signup and view all the answers

    What is the primary impact of vasodilation on the body’s blood pressure?

    <p>It reduces blood pressure.</p> Signup and view all the answers

    What happens to cardiac output when chemoreceptors trigger sympathetic stimulation due to hypoxia?

    <p>Cardiac output increases due to elevated sympathetic activity.</p> Signup and view all the answers

    What happens to baroreceptors when blood pressure decreases?

    <p>They become less stretched and send fewer impulses to the CVC.</p> Signup and view all the answers

    How does the cardiovascular center (CVC) respond when there is a decrease in blood pressure?

    <p>It decreases parasympathetic stimulation and increases sympathetic activity, raising heart rate and cardiac output.</p> Signup and view all the answers

    What physiological change occurs as a result of increased sympathetic activity when blood pressure is low?

    <p>Increased vascular resistance and cardiac output</p> Signup and view all the answers

    What happens when baroreceptors detect an increase in blood pressure?

    <p>They send more impulses to the CVC, stimulating parasympathetic activity.</p> Signup and view all the answers

    How does increased parasympathetic stimulation affect the heart rate and blood pressure?

    <p>It lowers heart rate, cardiac output, and promotes vasodilation, reducing blood pressure.</p> Signup and view all the answers

    Where are chemoreceptors that control blood pressure located?

    <p>In the carotid bodies and aortic bodies near the baroreceptors</p> Signup and view all the answers

    What effect does an increase in blood pressure typically have on heart rate?

    <p>It causes a decrease in heart rate.</p> Signup and view all the answers

    What would likely occur if baroreceptors are not functioning correctly?

    <p>There would be increased fluctuations in blood pressure.</p> Signup and view all the answers

    What effect does angiotensin II have on blood pressure?

    <p>It causes vasoconstriction and promotes water reabsorption.</p> Signup and view all the answers

    What is the primary function of atrial natriuretic peptide (ANP)?

    <p>To decrease blood pressure by promoting vasodilation and salt loss.</p> Signup and view all the answers

    Where is atrial natriuretic peptide (ANP) primarily produced?

    <p>The atria of the heart</p> Signup and view all the answers

    Which of the following correctly describes how blood pressure is influenced in the kidneys?

    <p>Reduced sodium reabsorption decreases blood pressure.</p> Signup and view all the answers

    What is the overall impact of elevated levels of atrial natriuretic peptide (ANP) on the cardiovascular system?

    <p>Decreases blood pressure and promotes diuresis.</p> Signup and view all the answers

    What triggers the release of renin from the kidneys?

    <p>Reduced blood flow to the kidneys</p> Signup and view all the answers

    Which enzyme is responsible for converting angiotensin I to angiotensin II?

    <p>ACE (Angiotensin-converting enzyme)</p> Signup and view all the answers

    What main effect does angiotensin II have on blood pressure regulation?

    <p>It acts as a vasoconstrictor and stimulates aldosterone secretion.</p> Signup and view all the answers

    How does aldosterone influence blood volume and pressure?

    <p>It increases sodium and water absorption, raising blood volume and blood pressure.</p> Signup and view all the answers

    What impact do epinephrine and norepinephrine have on cardiovascular function?

    <p>They increase cardiac output by raising heart rate and force of contraction while causing vasoconstriction.</p> Signup and view all the answers

    From which part of the body are epinephrine and norepinephrine released during sympathetic stimulation?

    <p>Adrenal medulla</p> Signup and view all the answers

    What physiological factor primarily stimulates the release of antidiuretic hormone (ADH)?

    <p>Low blood volume</p> Signup and view all the answers

    How does antidiuretic hormone (ADH) influence blood pressure?

    <p>It increases blood pressure by promoting water reabsorption.</p> Signup and view all the answers

    What is autoregulation in the context of blood pressure?

    <p>The ability of tissues to automatically adjust blood flow based on their needs</p> Signup and view all the answers

    What type of changes can influence autoregulation of blood flow?

    <p>Physical changes (e.g., warming and cooling) and chemical signals</p> Signup and view all the answers

    Which part of the heart generates action potentials that initiate the cardiac cycle?

    <p>Sinoatrial (SA) node</p> Signup and view all the answers

    What happens during the rapid filling phase of the ventricles?

    <p>The AV valves open, allowing blood to fill the ventricles rapidly</p> Signup and view all the answers

    What occurs during isovolumetric contraction in the cardiac cycle?

    <p>Intraventricular pressure rises while all valves are closed</p> Signup and view all the answers

    What is the function of M2 muscarinic receptors in the parasympathetic nervous system?

    <p>Slow down the heart</p> Signup and view all the answers

    Which neurotransmitter is primarily released by the sympathetic nervous system?

    <p>Noradrenaline (norepinephrine)</p> Signup and view all the answers

    What is the primary role of Purkinje fibers in the heart?

    <p>Spread the action potential through the ventricles for coordinated contraction</p> Signup and view all the answers

    During which phase of the cardiac cycle does isovolumetric relaxation occur?

    <p>At the end of ventricular systole when all valves are closed</p> Signup and view all the answers

    What happens to blood flow when vasodilation occurs?

    <p>Blood flow increases and blood pressure decreases</p> Signup and view all the answers

    What effect does parasympathetic activation have on the gastrointestinal (GI) tract?

    <p>Increases intestinal and gland activity</p> Signup and view all the answers

    What does the myogenic response refer to in blood flow regulation?

    <p>The muscle contraction that regulates blood vessel diameter in response to pressure changes</p> Signup and view all the answers

    Which type of blood vessel offers the highest resistance and contributes to a significant pressure drop?

    <p>Arterioles</p> Signup and view all the answers

    What occurs when the heart pumps more blood but the resistance in the arterioles remains the same?

    <p>Arterial pressure rises</p> Signup and view all the answers

    What is the effect of adrenaline released by the adrenal medulla during sympathetic activation?

    <p>Increases heart rate, force of contraction, and blood pressure</p> Signup and view all the answers

    What occurs immediately after the rapid filling phase of the ventricles?

    <p>Atrial systole</p> Signup and view all the answers

    What is the primary function of the AV node in the cardiac cycle?

    <p>To delay the transmission of the action potential</p> Signup and view all the answers

    How does ANP contribute to blood pressure regulation?

    <p>By decreasing blood pressure via vasodilation and salt excretion</p> Signup and view all the answers

    What structural feature of arteries helps maintain high pressure in the circulatory system?

    <p>Thick, muscular walls and connection to high-resistance arterioles</p> Signup and view all the answers

    What impact does the parasympathetic nervous system have on heart rate and blood pressure?

    <p>Decreases both heart rate and blood pressure</p> Signup and view all the answers

    What triggers the release of the renin-angiotensin-aldosterone system (RAAS)?

    <p>Low blood flow to the kidneys</p> Signup and view all the answers

    Which phase of the cardiac cycle is characterized by blood being ejected into the arteries?

    <p>Ventricular systole</p> Signup and view all the answers

    Which hormone promotes water reabsorption in the kidneys and increases blood pressure?

    <p>Antidiuretic hormone (ADH)</p> Signup and view all the answers

    What happens to baroreceptor activity when blood pressure rises?

    <p>It increases, sending more impulses to the cardiovascular center.</p> Signup and view all the answers

    What response is triggered when chemoreceptors detect low oxygen levels (hypoxia)?

    <p>Sympathetic stimulation increases heart rate and vasoconstriction.</p> Signup and view all the answers

    What occurs during the isovolumetric relaxation phase of the cardiac cycle?

    <p>The ventricles relax, and all valves are closed.</p> Signup and view all the answers

    Which of the following statements about the sympathetic nervous system is true?

    <p>It releases noradrenaline and stimulates an increase in heart rate and blood pressure.</p> Signup and view all the answers

    What physiological effect occurs with elevated levels of angiotensin II?

    <p>It stimulates aldosterone secretion from the adrenal cortex.</p> Signup and view all the answers

    What response occurs when plasma CO2 levels rise significantly?

    <p>Increased ventilation to help expel CO2</p> Signup and view all the answers

    Which respiratory function is primarily enhanced by the activity of the medulla oblongata?

    <p>Activation of diaphragm and intercostal muscles</p> Signup and view all the answers

    What is the expected physiological change following an increase in ventilation due to high CO2 levels?

    <p>Normalization of blood pH due to reduced CO2 partial pressure</p> Signup and view all the answers

    What effect does high CO2 concentration have on respiratory rate?

    <p>It stimulates an increase in respiratory rate for gas exchange</p> Signup and view all the answers

    What role do spinal cord motor neurons play in response to elevated CO2 levels?

    <p>They transmit signals from the medulla to enhance ventilation</p> Signup and view all the answers

    Which part of the brain is responsible for initiating the movement of the right thumb?

    <p>Left primary motor cortex</p> Signup and view all the answers

    What is the pathway of upper motor neurons (UMN) as they travel to the spinal cord?

    <p>Through the internal capsule, midbrain, brainstem, crossing over at the medulla</p> Signup and view all the answers

    At which structure do the majority of upper motor neurons cross to the opposite side of the body?

    <p>Medulla</p> Signup and view all the answers

    In which spinal cord tract are upper motor neurons primarily found?

    <p>Lateral corticospinal tract</p> Signup and view all the answers

    Where do upper motor neurons synapse with lower motor neurons in the spinal cord?

    <p>Anterior horn</p> Signup and view all the answers

    What stimulus activates chemoreceptors in the aortic and carotid bodies to signal the respiratory center?

    <p>Increase in arterial CO2 and decrease in blood pH</p> Signup and view all the answers

    What is the primary role of the respiratory center in the medulla oblongata?

    <p>To initiate an increase in ventilation</p> Signup and view all the answers

    What type of signal do chemoreceptors transmit to the respiratory center?

    <p>Electrochemical signals</p> Signup and view all the answers

    What is the primary trigger for the closing of the AV valves during ventricular systole?

    <p>Rapid rise in intraventricular pressure</p> Signup and view all the answers

    What physiological effect occurs as a result of elevated carbon dioxide levels in the blood?

    <p>Activation of chemoreceptors leading to increased ventilation</p> Signup and view all the answers

    How does a high concentration of carbon dioxide affect blood pH levels?

    <p>It decreases blood pH, leading to acidosis</p> Signup and view all the answers

    What occurs when the pacemaker activity of the sinoatrial node spreads through the atria?

    <p>Atrial systole occurs, leading to contraction of the atria</p> Signup and view all the answers

    Which chemical is primarily detected by chemoreceptors that signals the need for increased ventilation?

    <p>Carbon dioxide (CO2)</p> Signup and view all the answers

    Which of the following best describes the function of upper motor neurons (UMN)?

    <p>Initiate voluntary motor movements from the brain to the spinal cord</p> Signup and view all the answers

    What is the role of the lower motor neuron (LMN) in the movement of the right thumb?

    <p>To directly target and activate the muscles responsible for thumb movement</p> Signup and view all the answers

    What type of signal is sent from the medulla oblongata to the respiratory muscles when increased ventilation is needed?

    <p>Motor neuron signals via the spinal cord</p> Signup and view all the answers

    What is the primary response when the arterial partial pressure of CO2 increases?

    <p>Increase in ventilation to expel CO2 and normalize pH</p> Signup and view all the answers

    What is the main function of the sinoatrial (SA) node in the heart?

    <p>To act as the pacemaker and generate action potentials</p> Signup and view all the answers

    Where are chemoreceptors that control breathing primarily located?

    <p>In the carotid bodies and aortic bodies</p> Signup and view all the answers

    What happens during isovolumetric contraction in the cardiac cycle?

    <p>The ventricles contract with all valves closed</p> Signup and view all the answers

    What role does the medulla oblongata play in regulating respiratory rhythm?

    <p>It integrates sensory input from the body</p> Signup and view all the answers

    Study Notes

    Hypothalamus-Pituitary-Thyroid Axis

    • The Hypothalamus-Pituitary-Thyroid (HPT) axis is a complex regulatory system that controls the production and release of thyroid hormones, T3 (triiodothyronine) and T4 (thyroxine).
    • When levels of T3 and T4 in the blood are low, the hypothalamus is signaled to release thyrotropin-releasing hormone (TRH).
    • TRH travels to the anterior pituitary gland, stimulating the release of thyroid-stimulating hormone (TSH).
    • TSH acts on the thyroid gland, prompting the release of T3 and T4.
    • This feedback loop ensures that thyroid hormone levels are maintained within a normal range.
    • When T3 and T4 levels increase, they suppress the release of TRH and TSH, leading to a decrease in thyroid hormone production.

    Hypothalamus Pituitary Axis and Thyroid Hormone Regulation

    • Low thyroid hormone levels (T3 and T4) trigger a chain reaction within the body.
    • Hypothalamus detects low T3 and T4 levels and responds by releasing thyrotropin-releasing hormone (TRH).
    • TRH travels to the anterior pituitary gland where it stimulates the release of thyroid-stimulating hormone (TSH).
    • TSH targets the thyroid gland prompting it to produce and release more T3 and T4.
    • This increased thyroid hormone production ultimately leads to the restoration of normal thyroid hormone levels in the body.
    • High T3 levels act as a negative feedback mechanism, inhibiting further TSH release from the anterior pituitary gland, preventing overproduction of thyroid hormones.

    Hypocalcaemia

    • Low levels of calcium in the blood stimulate the parathyroid glands to release parathyroid hormone (PTH).

    PTH Action

    • PTH promotes bone resorption by activating osteoclasts.
    • Osteoclasts degrade bone matrix, releasing calcium and phosphate into the bloodstream.
    • PTH enhances calcium absorption from the intestines.
    • PTH stimulates vitamin D production in the kidneys, further increasing calcium absorption from the intestines and calcium reabsorption in the kidneys.

    Negative Feedback

    • Rising calcium levels in the blood inhibit the release of PTH, creating a negative feedback loop.

    Hypocalcaemia

    • Low calcium levels in the body stimulate the release of parathyroid hormone (PTH) from the parathyroid glands.
    • PTH increases calcium levels in the blood by acting on bones, intestines, and kidneys.
    • In bones, PTH activates osteoclasts which break down bone matrix, releasing calcium and phosphate into the blood.
    • In the intestines, PTH enhances calcium absorption from food.
    • In the kidneys, PTH promotes vitamin D activation, which further increases calcium absorption from food and calcium reabsorption in the kidneys.
    • Rising calcium levels in the bloodstream inhibit PTH release, creating a negative feedback loop that maintains calcium homeostasis.

    The Renin-Angiotensin-Aldosterone System (RAAS)

    • The RAAS is a complex hormonal system that regulates blood pressure and fluid balance by modulating blood volume and vascular tone.
    • The main components of the RAAS are:
      • Renin, an enzyme produced by the kidneys
      • Angiotensinogen, a protein produced by the liver
      • Angiotensin-converting enzyme (ACE), an enzyme primarily found in the lungs
      • Angiotensin II, a potent vasoconstrictor
      • Aldosterone, a hormone produced by the adrenal cortex
    • Renin is released from the kidneys in response to low blood pressure or low blood volume.
    • Renin converts angiotensinogen, a protein found in the blood, into angiotensin I.
      • Angiotensin I is then converted to angiotensin II by ACE in the lungs.
    • Angiotensin II acts on blood vessels to cause vasoconstriction, leading to an increase in blood pressure.
      • It also stimulates the adrenal cortex to produce aldosterone.
    • Aldosterone acts on the kidneys to increase sodium and water reabsorption, leading to an increase in blood volume and blood pressure.
    • The RAAS is a powerful system that helps to maintain blood pressure within a normal range.
      • However, overactivation of the RAAS can contribute to hypertension and other cardiovascular problems.

    Angiotensin II

    • Angiotensin II, a potent vasoconstrictor, is the product of the RAAS.
    • It acts on blood vessels causing vasoconstriction, leading to an increase in blood pressure.
    • Additionally, it stimulates the adrenal cortex to produce aldosterone.

    Aldosterone

    • Aldosterone is a steroid hormone produced by the adrenal cortex under the influence of Angiotensin II.
    • Its main function is to increase sodium and water reabsorption in the kidney.
    • This action leads to an increase in blood volume and blood pressure.
      • Aldosterone also stimulates potassium excretion.
    • Aldosterone contributes to the maintenance of electrolyte balance and blood pressure.

    ACE Inhibitors

    • ACE inhibitors are medications that block the action of ACE, preventing the conversion of angiotensin I to angiotensin II.
    • By inhibiting angiotensin II formation, ACE inhibitors reduce vasoconstriction and decrease aldosterone production.
    • This ultimately leads to a decrease in blood pressure.

    Angiotensin Receptor Blockers (ARBs)

    • ARBs are a different type of drug that directly block the action of angiotensin II at its receptors.
    • ARBs work similarly to ACE inhibitors by reducing vasoconstriction and aldosterone production, leading to a decrease in blood pressure.
    • Both ACE inhibitors and ARBs are frequently prescribed for the management of hypertension, heart failure, and other cardiovascular conditions.

    Cortisol and Protein Metabolism

    • Cortisol increases the breakdown of proteins, specifically in muscle fibers.
    • This process aims to provide amino acids as fuel for energy production.

    Cortisol and Glucose Regulation

    • During stress, cortisol helps to increase blood glucose levels through a process called gluconeogenesis.
    • It achieves this by converting amino acids or lactic acid into glucose, which is then released into the bloodstream.

    Cortisol and Fat Metabolism

    • Cortisol promotes lipolysis, the breakdown of triglycerides into fatty acids and glycerol.
    • These free fatty acids can be used as an alternative energy source by the body.

    Cortisol and Stress Response

    • Cortisol plays a significant role in the body's stress response.
    • It aids in resisting stress by providing substrates for energy production, ensuring the body has sufficient fuel to cope with stressful situations.

    Cortisol as an Anti-Inflammatory

    • Cortisol has anti-inflammatory effects by suppressing the immune system.
    • This helps to prevent an overactive immune response which could damage tissues during stress.

    Blood Glucose Regulation

    • Blood glucose levels increase after eating due to the breakdown of carbohydrates into glucose.

    Insulin

    • Insulin is a hormone secreted by the pancreas when blood glucose levels are high.
    • Insulin stimulates the liver to convert glucose into glycogen for storage, lowering blood glucose levels.

    Glucagon

    • Glucagon is a hormone secreted by the pancreas when blood glucose levels are low.
    • Glucagon converts glycogen back into glucose and releases it into the bloodstream, increasing blood glucose levels.

    Glucose Regulation

    • Blood glucose levels increase after eating due to the digestion and absorption of carbohydrates.
    • Insulin is released by the pancreas when blood glucose levels are high, facilitating the uptake of glucose by cells and its storage as glycogen in the liver.
    • Insulin's primary function is to lower blood glucose levels by promoting glucose uptake and storage.
    • Glucagon is released by the pancreas when blood glucose levels are low, stimulating the breakdown of glycogen stored in the liver, releasing glucose into the bloodstream. Glucagon's primary function is to increase blood glucose levels.
    • Glucagon and insulin work antagonistically to maintain blood glucose levels within a narrow range.

    Parietal Cells: Structure and Function

    • Parietal cells are specialized epithelial cells found in the stomach lining.
    • Their primary function is to secrete hydrochloric acid (HCl) into the gastric lumen.
    • HCl is essential for digestion, aiding in the breakdown of food and activation of pepsinogen.
    • Parietal cells possess a unique structure that allows them to perform this vital task.

    Parietal Cell Structure

    • Parietal cells exhibit a highly developed basolateral surface with multiple folds and microvilli.
    • This surface is rich in receptors that respond to various signals regulating HCl secretion.
    • Gastrin, acetylcholine, and histamine are prominent stimulatory signals that trigger HCl production.
    • Parietal cells are connected to the gastric lumen through a gastric pit, a small opening that facilitates the release of secreted HCl.

    Ion Transport

    • Proton pumps are integral membrane proteins found in parietal cells.
    • These pumps actively transport hydrogen ions (H+) out of the cell into the gastric lumen.
    • This process is coupled with the simultaneous transport of potassium ions (K+) into the cell.
    • At the basolateral surface, parietal cells engage in an ion exchange mechanism, transporting chloride ions (Cl-) into the cell and bicarbonate ions (HCO3-) out of the cell.

    HCl Production

    • Hydrochloric acid is formed in the gastric lumen through the combination of hydrogen ions (H+) and chloride ions (Cl-).
    • The parietal cell's proton pump and the chloride ion transporter play crucial roles in this process.
    • The resulting HCl maintains acidic gastric conditions, optimal for digestion and enzyme activation.

    Parietal Cell Receptors

    • Parietal cells possess H2, gastrin, and acetylcholine receptors on their basolateral surface.

    Parietal Cell Structure

    • Parietal cells open into the gastric lumen via a structure called the gastric pit.

    Parietal Cell Ion Exchange

    • The basolateral surface of parietal cells facilitates an exchange of chloride ions into the cell and bicarbonate ions out of the cell.

    Parietal Cell Proton Pump

    • Located within parietal cells, the proton pump actively transports hydrogen ions out of the cell and potassium ions into the cell.

    Hydrochloric Acid Formation

    • Hydrochloric acid is generated in the gastric lumen by the combination of hydrogen ions and chloride ions.

    Swallowing Phases

    • Swallowing consists of three stages:
      • Oral phase: Voluntary - Food is chewed and manipulated by the tongue to form a bolus before being moved to the back of the mouth.
      • Pharyngeal phase: Involuntary - The bolus is moved through the oropharynx and into the esophagus. This stage is triggered by the bolus stimulating the soft palate and the back of the throat.
      • Esophageal phase: Involuntary - The bolus passes through the esophagus to the stomach.

    Oropharyngeal Phase

    • The tongue plays a key role in moving food back through the mouth and into the valleculae (depressions located at the base of the tongue).

    Preventing Food From Entering the Trachea

    • The epiglottis is a flap of cartilage that closes over the opening of the trachea (windpipe) during swallowing, preventing food from entering the airways.

    Esophageal Phase

    • Peristalsis: A series of muscular contractions and relaxations in the esophagus propels the bolus towards the stomach. Gravity also contributes to the movement of the bolus.
    • Sphincters: Muscular rings that regulate the passage of food through the digestive tract.

    Sphincters Involved in Swallowing

    • Upper esophageal sphincter (UES): Relaxes to allow food to pass from the pharynx into the esophagus.
    • Lower esophageal sphincter (LES): Relaxes to allow food to enter the stomach from the esophagus.

    Swallowing Phases

    • The oropharyngeal phase of swallowing involves the tongue pushing food back into the mouth and into the valleculae.
    • The epiglottis closes during swallowing to prevent food from entering the trachea.
    • The oesophageal phase of swallowing relies on peristaltic action and gravity to move food down the oesophagus.
    • The upper oesophageal sphincter must open to allow food to move into the oesophagus.
    • The lower oesophageal sphincter must open to allow food to enter the stomach from the oesophagus.

    Carbohydrate Digestion

    • Salivary and pancreatic amylases break down starch and glycogen into disaccharides.
    • Sucrase breaks down sucrose into glucose and fructose in the small intestine.
    • Monosaccharides enter the capillaries after digestion by facilitated diffusion.
    • Glucose is stored as glycogen in the liver or used for energy in the citric acid cycle.

    Protein Digestion

    • Proteins are initially digested into oligopeptides.
    • Amino acids enter cells during absorption by sodium co-transport.
    • Amino acids are transported to other cells for protein synthesis.

    Fat Digestion

    • Lipase breaks down fat into fatty acids and glycerol.
    • Bile salts, phospholipids, and cholesterol form micelles.
    • Micelles facilitate the absorption of fatty acids and monoglycerides across the cell membrane.
    • Chylomicrons are secreted into the basolateral space and transported via lacteals.
    • Bile salts emulsify fats, making them easier for lipase to digest.

    Additional Facts

    • Lactase breaks down lactose into glucose and galactose.
    • Enterokinase activates trypsinogen into trypsin in the small intestine.
    • The majority of protein digestion occurs in the small intestine.
    • Chylomicrons are primarily composed of triglycerides, cholesterol, and proteins.
    • Fatty acids and monoglycerides enter intestinal cells by simple diffusion.

    Vomiting Reflex and Receptors

    • The Chemoreceptor Trigger Zone (CTZ) is located in the medulla oblongata and receives signals from the blood.
    • The CTZ communicates with the vomiting center, triggering the vomiting reflex.
    • The vomiting center, in the medulla oblongata, coordinates the physical actions of vomiting.
    • Vomiting involves contraction of the diaphragm and abdominal walls, resulting in increased abdominal pressure.
    • The lower esophageal sphincter relaxes during vomiting to allow the contents of the stomach to move upward.
    • The glottis closes to prevent regurgitated contents from entering the airway.
    • The soft palate closes to prevent regurgitated contents from entering the nasal cavity.
    • The 5HT3 receptor (serotonin receptor) is a key target for anti-sickness medications.
    • Other receptors involved in the vomiting reflex include D2 receptors (dopamine) and histamine receptors.
    • D2 receptors are targeted by anti-emetics like metoclopramide.
    • Histamine receptors are targeted by antihistamines like promethazine.

    Hypothalamus-Pituitary-Gonad Axis in Males

    • Gonadotropin-releasing hormone (GnRH) is released by the hypothalamus and targets the anterior pituitary.
    • Follicle-stimulating hormone (FSH) is produced by the anterior pituitary and targets the Sertoli cells in the testes.
    • Sertoli cells release androgen binding protein (ABP) in response to FSH.
    • ABP maintains high testosterone levels around spermatogenic cells which are responsible for sperm production.
    • Luteinizing hormone (LH) is produced by the anterior pituitary and targets the Leydig cells in the testes.
    • Leydig cells then produce testosterone in response to LH.
    • Increased testosterone levels inhibit GnRH release from the hypothalamus, creating a negative feedback loop.
    • Inhibin is produced by the Sertoli cells and acts as a baroreceptor regulating sperm count by preventing FSH and GnRH release when sperm count is high.
    • Testosterone is the main male sex hormone that plays a critical role in the development of male sex organs and secondary sexual characteristics.

    Spermatogenesis Overview

    • Spermatogenesis is the process of producing sperm in the testes.
    • It starts with spermatogonia - undifferentiated germ cells.

    Spermatogonia

    • Located in contact with the basal lamina of seminiferous tubules.
    • Undergo mitosis until puberty, producing more spermatogonia.
    • After puberty, some spermatogonia differentiate into Type B spermatogonia.

    Type B Spermatogonia

    • Undergo mitosis to form primary spermatocytes.
    • Primary spermatocytes undergo meiosis I, producing haploid secondary spermatocytes.

    Meiosis

    • Meiosis I reduces the chromosome number from diploid to haploid.
    • Meiosis II divides the secondary spermatocytes into haploid spermatids.

    Spermatids

    • Undergo spermiogenesis, transforming into spermatozoa.

    Spermiogenesis

    • Spermatids elongate, develop an acrosome (cap filled with enzymes for penetrating the egg), and form a flagellum (tail).
    • Cytoplasmic baggage is removed to make the spermatozoon more streamlined.

    Outcome

    • Spermatogenesis produces sperm - mature, motile gametes.
    • Each primary spermatocyte results in four haploid spermatozoa.

    Spermatogenesis

    • Spermatogenesis is the process of producing sperm in the testes.
    • Spermatogonia are the outermost cells in contact with the basal lamina in a seminiferous tubule
    • Spermatogonia divide mitotically until puberty.
    • Type A daughter cells remain at the basal lamina and continue to divide
    • Type B daughter cells move away from the basal lamina toward the lumen and become primary spermatocytes.
    • Primary spermatocytes undergo meiosis I, a type of cell division that reduces the number of chromosomes by half, and produce two haploid secondary spermatocytes.
    • Secondary spermatocytes undergo meiosis II, a type of cell division that separates the sister chromatids, and produce four haploid spermatids.
    • Spermiogenesis is the final phase of spermatogenesis, and involves the differentiation of spermatids into spermatozoa.
    • During spermiogenesis, spermatids elongate, lose excess cytoplasm, and develop a flagellum or tail, becoming spermatozoa.
    • Spermatozoa are the mature sperm cells that are capable of fertilizing an egg.

    Spermatogenesis

    • The process of spermatogenesis occurs in the seminiferous tubules of the testes and involves a series of cell divisions.
    • Spermatogonia, located in the basal lamina, are the starting point for spermatogenesis.
    • These cells undergo mitosis until puberty, producing two daughter cells: Type A and Type B spermatogonia.
    • Type A cells remain in the basal lamina to continue producing more spermatogonia, ensuring a continuous supply of these cells.
    • Type B cells undergo meiosis I to become primary spermatocytes, which are diploid cells with a full set of chromosomes.
    • Primary spermatocytes undergo meiosis I, a process of cell division reducing the chromosome number to half, producing haploid secondary spermatocytes.
    • Secondary spermatocytes then undergo meiosis II, further reducing the chromosome number, resulting in four haploid spermatids.
    • Spermiogenesis is the final stage of spermatogenesis, where the spermatids undergo a series of transformations to become mature spermatozoa.
    • These transformations include elongation, removal of unnecessary cytoplasm, and development of a tail, which allows for sperm motility.
    • Each type B cell produces four spermatids, highlighting the efficiency of spermatogenesis in producing mature sperm cells.
    • This process is crucial for male fertility and the production of viable sperm for successful fertilization.

    Oogenesis: Key Facts

    • Oogenesis: The process by which female gametes (ova or eggs) are produced within the ovaries.
    • Oogonium: The initial diploid cell (2n) that undergoes mitosis to produce primary oocytes.
    • Primary Oocyte: Arrests in Prophase I of meiosis in utero.
    • Ovulation: After puberty, each month a primary oocyte completes Meiosis I, resulting in a haploid (n) secondary oocyte and a polar body.
    • Secondary Oocyte: Arrests in Metaphase II of meiosis, waiting to be fertilized.
    • Fertilization: Completion of Meiosis II occurs when a sperm cell fertilizes the secondary oocyte. This forms a diploid (2n) zygote.
    • Meiosis Completion: Meiosis II is only completed if the secondary oocyte is fertilized.
    • Completion Trigger: The presence of a sperm cell is the key trigger for restarting meiosis II.

    Follicular Development Stages

    • Primordial follicles: Contain a primary oocyte surrounded by a single layer of flattened follicular cells.
    • Primary follicles: Contain a primary oocyte, zona pellucida, and a single layer of cuboidal follicular cells. The theca interna and externa begin to develop.
    • Secondary (early antral) follicles: Contain a primary oocyte, zona pellucida, granulosa cells, theca interna and externa, and a small antrum. The antrum starts to fill with follicular fluid.
    • Graafian (vesicular) follicles: Contain a secondary oocyte surrounded by the corona radiata and cumulus oophorus, a large antrum filled with follicular fluid, and a well-developed theca interna and externa. This is the stage where ovulation occurs.

    Post Ovulation Stages

    • Corpus luteum: Forms after ovulation and secretes progesterone to maintain the uterine lining for potential pregnancy.
    • Corpus albicans: A degenerating corpus luteum, indicating the end of hormone production.

    Other Key Structures and Functions

    • Zona pellucida: A protective layer surrounding the oocyte, forming during the primary follicle stage.
    • Corona radiata and cumulus oophorus: Surround the oocyte within the Graafian follicle and support it during ovulation.
    • Theca interna: Produces androgens that are converted into estrogens by granulosa cells.
    • Theca externa: A protective outer layer of the follicle.
    • Antrum: A fluid-filled cavity within the secondary and Graafian follicles.

    Ovulation

    • Ovulation is the process of releasing a secondary oocyte from a mature Graafian follicle.
    • Day 14 of a typical 28-day menstrual cycle marks ovulation.

    Hormonal Triggering

    • A surge in luteinizing hormone (LH) primarily triggers ovulation.
    • The theca interna, a layer of cells in the follicle wall, contracts, helping expel the secondary oocyte.

    Mechanical Processes

    • Follicular fluid expansion and pressure contribute to follicular wall rupture.
    • Enzymatic proteolysis of the follicular wall also aids in its breakdown.

    Post-Ovulation

    • The ruptured follicle transforms into the corpus luteum.
    • The corpus luteum produces progesterone, crucial for preparing the uterus for pregnancy.
    • If fertilization doesn't occur, the corpus luteum degenerates into the corpus albicans.

    Follicular Phase

    • The follicular phase encompasses the initial stages of the menstrual cycle.
    • Ovulation marks the end of the follicular phase.

    Key Facts

    • The follicular phase involves follicle development and selection of a dominant follicle.
    • The follicle contains a secondary oocyte, the potential egg cell.
    • Ovulation is a complex event with hormonal and mechanical components.
    • The post-ovulatory phase, called the luteal phase, is marked by corpus luteum activity.

    Hypothalamus-Pituitary-Gonad Axis in Females

    • Gonadotrophin-releasing hormone (GnRH) is released by the hypothalamus and targets the anterior pituitary.
    • Follicle-stimulating hormone (FSH) is released by the anterior pituitary and stimulates growth of granulosa cells and initial development of primary ovarian follicles.
    • FSH up-regulates LH receptors in granulosa cells, contributing to follicular development.
    • Luteinizing hormone (LH) is released by the anterior pituitary and induces ovulation, stimulates production of oestrogens and progesterone.
    • The LH surge occurs on day 13/14 of the menstrual cycle and triggers ovulation.
    • Anti-Mullerian hormone (AMH) is produced by granulosa cells and prevents the development of surrounding follicles.
    • Theca cells produce androgens which are converted to oestrogen in granulosa cells.
    • LH stimulates the production of progesterone by the corpus luteum.
    • Oestrogen has a negative feedback mechanism on FSH production by acting on the hypothalamus and anterior pituitary.
    • The LH surge induces ovulation and marks the transition from the follicular to luteal phase in the menstrual cycle.

    The Menstrual Cycle

    • The menstrual cycle is a series of events that prepare the female body for potential pregnancy.
    • The cycle is controlled by hormones and regulated by feedback loops and lasts approximately 28 days.
    • The cycle is divided into four stages: menstrual, proliferative, secretory, and luteal.

    Menstrual Stage

    • This is the first stage of the menstrual cycle and starts with the shedding of the uterine lining, specifically the stratum functionalis.
    • This shedding occurs due to a decrease in progesterone levels.
    • This stage marks the start of a new cycle.

    Proliferative Stage

    • The proliferative stage is characterized by the repair and growth of the stratum functionalis.
    • This growth is stimulated by estrogen, produced by developing ovarian follicles.
    • This stage culminates in ovulation, the release of a mature egg from the ovary.

    Secretory Stage

    • This stage follows ovulation and is characterized by increased uterine receptivity to a fertilized egg.
    • The uterine lining becomes thicker and more vascular, preparing for implantation.
    • Increased glandular secretions provide a nutrient-rich environment for a potential embryo.
    • This stage is stimulated by progesterone, produced by the corpus luteum, a temporary structure formed in the ovary after ovulation.

    Luteal Stage

    • The luteal stage corresponds with the secretory stage.
    • It is marked by a decline in estrogen and rise in progesterone.
    • The corpus luteum remains active, secreting progesterone.

    Pregnancy

    • If fertilization occurs, the fertilized egg implants in the uterine lining.
    • The developing placenta produces human chorionic gonadotropin (hCG) which maintains the corpus luteum, preventing it from degrading.
    • hCG takes over the role of LH, continuing progesterone production.
    • Progesterone levels remain high, maintaining the uterine lining for pregnancy.

    No Pregnancy

    • If fertilization does not occur, the corpus luteum degrades as hCG is not produced.
    • This leads to a decline in progesterone levels which causes the stratum functionalis to be shed, marking the start of a new menstrual cycle.

    Calcium Regulation and Bone Remodeling

    • Hypocalcemia is a condition characterized by low calcium levels in the blood.
    • Parathyroid hormone (PTH) is released by the parathyroid glands in response to hypocalcemia.
    • PTH activates osteoclasts , specialized cells responsible for bone resorption (breakdown), to release calcium and phosphate into the blood, raising blood calcium levels.
    • Osteoclasts secrete proteolytic enzymes and hydrogen ions to break down bone matrix.
    • The process of bone degradation triggered by PTH is crucial for restoring normal blood calcium levels.

    Bone Fracture Repair

    • Bone fracture repair initiates with hematoma formation, a blood clot that forms at the fracture site.
    • The hematoma is gradually replaced by a fibrocartilage callus, a soft callus made of cartilage and collagen fibers that acts as a temporary splint to stabilize the fracture.
    • Bony callus formation follows, where the fibrocartilage callus is gradually replaced by a hard callus of woven bone.
    • Bone remodeling is the final stage where the woven bone is replaced with lamellar bone, restoring the bone's original shape and strength.

    Hypocalcemia

    • Low levels of calcium in the body
    • Stimulates the parathyroid gland to release parathyroid hormone (PTH)

    Parathyroid Hormone (PTH)

    • Released from the parathyroid gland in response to low calcium levels
    • Activates osteoclasts to break down bone matrix, releasing calcium into the blood
    • Increases calcium absorption from the intestines
    • Increases calcium reabsorption from kidney tubules

    Osteoclasts

    • Cells that break down bone matrix
    • Secrete proteolytic enzymes and hydrogen ions to digest bone matrix
    • Activity is stimulated by PTH

    Bone Fracture Repair

    • Hematoma formation: A blood clot forms at the fracture site
    • Fibrocartilage callus formation: A soft callus of fibrocartilage forms to stabilize the fracture
    • Bony callus formation: The fibrocartilage callus is replaced by a hard callus of new bone
    • Bone remodeling: The bony callus is remodeled to restore the original shape and strength of the bone

    Bone Remodeling

    • Bone remodeling is a continuous process that involves the breakdown and rebuilding of bone tissue.
    • It is essential to maintain bone health by controlling calcium and phosphate homeostasis, repairing damaged bone, and adapting bone shape to mechanical stress.

    Cells Involved in Bone Remodeling

    • Osteoclasts: Large, multinucleated cells responsible for bone resorption (breakdown).
      • Secrete proteolytic enzymes and hydrogen ions to break down bone matrix.
      • Release calcium and phosphate ions into the bloodstream, contributing to calcium homeostasis.
    • Osteoblasts: Bone-forming cells that secrete osteoid (unmineralized bone matrix).
      • Osteoid undergoes mineralization, becoming hard bone tissue.

    Bone Remodeling Process

    • Resorption: Osteoclasts break down bone matrix, releasing calcium and phosphate into the bloodstream.
    • Formation: Osteoblasts produce new bone tissue by secreting osteoid that mineralizes.
    • Coupling: The activities of osteoclasts and osteoblasts are tightly coupled, ensuring balanced bone formation and resorption.

    Calcium Homeostasis

    • Osteoclasts play a crucial role in calcium homeostasis by releasing calcium into the bloodstream.
    • Calcium levels are controlled by hormones like parathyroid hormone (PTH) and calcitonin.

    Bone Mineralization

    • Mineralization is the process by which osteoid hardens into bone tissue.
    • Calcium and phosphate ions from the bloodstream are deposited into the osteoid, making it rigid.

    Endochondral Ossification

    • Primary ossification occurs in the diaphysis (shaft) of a long bone

    • Step 1: Osteoblasts in the periosteum secrete osteoid to form a bone collar around the diaphysis

    • Step 2: As the bone collar forms, cartilage in the diaphysis calcifies, cells die

    • Step 3: Periosteal bud invades the calcified cartilage. This bud contains blood vessels, nerves, osteoclasts, osteoblasts, and red marrow cells.

    • Step 4: Spongy trabeculae form as osteoblasts deposit bone matrix on the calcified cartilage and the medullary cavity forms

    • Step 5: As the diaphysis elongates, the medullary cavity expands, creating a hollow space for the marrow

    Secondary Ossification

    • Secondary ossification occurs in the epiphyses (ends) of long bones.

    • Step 1: Begins around birth, with blood vessels invading the epiphysis.

    • Step 2: Similar to primary ossification, spongy bone forms in place of calcified cartilage

    • Step 3: The epiphysis is filled with spongy bone, but a thin layer of cartilage remains on the articulating surfaces (articular cartilage) and the epiphyseal plate (where bone lengthening occurs)

    Epiphyseal Plate

    • The epiphyseal plate is responsible for the longitudinal growth of long bones.

    • It is composed of hyaline cartilage and has five zones:

      • Resting zone: Cartilage cells are inactive
      • Proliferation zone: Cartilage cells divide rapidly
      • Hypertrophic zone: Cartilage cells enlarge
      • Calcification zone: Cartilage matrix calcifies
      • Ossification zone: Osteoblasts replace calcified cartilage with bone

    Summary of Key Functions in Endochondral Ossification

    • Osteoblasts: Secrete bone matrix to form the bone collar, spongy trabeculae, and ultimately the diaphysis
    • Osteoclasts: Break down calcified cartilage, creating the medullary cavity
    • Blood vessels: Bring nutrients and oxygen to the developing bone
    • Nerves: Innervate the bone
    • Red marrow cells: Produce blood cells

    Osteoblast Endocrine Function

    • Osteoblasts are bone-building cells.
    • They secrete hormones that regulate bone metabolism and have a role in overall metabolic health.
    • Two primary hormones secreted by osteoblasts are osteocalcin and fibroblast growth factor 23 (FGF23).

    Osteocalcin

    • Osteocalcin promotes insulin production by pancreatic beta cells.
    • It also stimulates insulin sensitivity.
    • It promotes glucose uptake by enhancing insulin production.
    • Osteocalcin levels are reduced in individuals with type 2 diabetes.
    • Osteocalcin triggers the release of adiponectin from adipocytes, which restricts fat storage and improves insulin sensitivity.

    FGF23

    • FGF23 regulates phosphate reabsorption in the kidneys.
    • This ensures there is a balance of phosphate in the body.
    • This contributes to bone health and mineral homeostasis.

    Interaction between Osteocalcin and Insulin

    • Insulin activates osteocalcin.
    • This creates a two-way synergistic mechanism where osteocalcin promotes insulin production and insulin activates osteocalcin.
    • This interaction contributes to the regulation of blood sugar levels and overall metabolic health.

    Muscle Contraction and Excitation-Contraction Coupling

    • Neural stimulation initiates excitation-contraction coupling in muscle cells by causing a wave of depolarization across the sarcolemma.
    • Sarcoplasmic reticulum (SR) is responsible for releasing calcium into the cytoplasm during muscle contraction.
    • Calcium binds to troponin, which causes a change in its shape and moves tropomyosin, exposing myosin binding sites on actin.
    • Myosin, when bound to actin, forms cross-bridges.
    • Power stroke, during which the myosin head bends, pulls the actin filament, and shortens the sarcomere.
    • After ADP and inorganic phosphate are released, a new ATP molecule binds to the myosin head, causing detachment of the cross bridge.
    • Hydrolysis of ATP by myosin is required for myosin to return to its erect (cocked) state.
    • Action potential stops leading to calcium being pumped back into the sarcoplasmic reticulum.
    • Tropomyosin moves back over the myosin binding sites on actin, preventing cross bridge formation and leading to muscle relaxation.

    Osteoarthritis: Joint Degradation and Pain

    • Cartilage Degradation: Cartilage in osteoarthritis becomes fragile and prone to mechanical wear, leading to the degeneration of the protective layer on joint surfaces.
    • Synovial Fluid Leakage: Synovial fluid leaking into bone cracks can exacerbate joint damage and contribute to cyst formation.
    • Osteophytes: Bony nodules called osteophytes form in osteoarthritis, altering biomechanics, disrupting the joint, and causing inflammation and pain.
    • Consequences of Cartilage Loss: Without cartilage, bones rub directly against each other, leading to mechanical wear, cracking, and further joint damage.
    • Osteoarthritis Symptoms: The primary symptoms of osteoarthritis stem from the changes in joint structure. Stiffness, inflammation, and pain are common consequences.
    • Osteophyte Impact: Osteophytes contribute to joint deformation and limit movement, exacerbating the progression of osteoarthritis.
    • Inflammatory Triggers: Osteoarthritis pain and inflammation are triggered by the altered biomechanics due to joint deformation.
    • Progressive Nature: Osteoarthritis progresses due to the gradual degeneration of cartilage, leading to mechanical wear and disruptive joint changes.
    • Key Takeaway: Osteoarthritis is a degenerative joint disease, characterized by cartilage breakdown, bone changes, and inflammation, resulting in pain and limited movement.

    Muscle Characteristics

    • Excitability: The ability of muscle tissue to respond to a stimulus, like a chemical signal such as a neurotransmitter. This is needed for muscle activation.

    • Contractility: The unique ability of muscle tissue to shorten forcefully when adequately stimulated. This is what allows muscles to produce movement.

    • Extensibility: The capacity of muscle tissue to be stretched beyond its resting length. This is necessary for muscles to lengthen and return to their original position.

    • Elasticity: The ability of muscle tissue to recoil and return to its original resting length after being stretched. This helps to maintain muscle shape and allows for smooth movement.

    • Contractility is essential for maintaining posture and supporting movement.

    • Muscle rigidity is not a muscle characteristic as it is not a natural property of muscle tissue, rather an abnormal state.

    Glomerular Filtration

    • Glomerular filtration is the process of filtering blood in the kidneys, specifically the volume of filtrate formed per minute.
    • This process is driven by hydrostatic pressure within the glomerulus.
    • Glomerular Filtration Rate (GFR) is tightly regulated to maintain homeostasis and blood pressure.

    Regulation of GFR

    • Intrinsic control refers to mechanisms within the kidneys that directly control GFR, ensuring constant filtration.
    • Extrinsic control involves hormonal and nervous system influences on GFR.
    • Kidneys maintain a stable GFR despite changes in blood pressure through adjusting blood flow resistance by constricting or dilating blood vessels.

    Intrinsic Control

    • Myogenic feedback mechanism responds to changes in blood pressure within the afferent arteriole, either constricting or relaxing smooth muscle, leading to changes in blood flow resistance.
    • Tubuloglomerular feedback mechanism monitors the concentration of salt in the tubule fluid at the macula densa.
    • The macula densa acts as a sensor, detecting changes in salt concentration and signaling the afferent arteriole to adjust its diameter.
    • If GFR is too high, the tubules might not have enough time to reabsorb necessary substances, leading to potential loss in urine.

    Myogenic Response

    • The myogenic response is triggered by changes in blood pressure within the afferent arteriole.

    Glomerular Filtration

    • The process by which fluid and solutes are filtered from the blood in the glomerulus, forming filtrate.
    • Driven by hydrostatic pressure present in the glomerular capillaries.
    • Regulating GFR (Glomerular Filtration Rate) crucial for maintaining blood pressure, electrolyte balance, and overall homeostasis.

    Intrinsic Regulation of GFR

    • Controls GFR directly without using external factors.

    • Myogenic Feedback Mechanism:

      • Afferent arterioles smooth muscle contracts in response to increased blood pressure.
      • Constricting the vessel, reduces blood flow to the glomerulus and lowers filtration rate.
      • Facilitates the regulation of GFR.

    • Tubuloglomerular Feedback (TGF) Mechanism:

      • Macula densa, a specialized area in the distal tubule monitors the concentration of salt in tubule fluid.
      • If salt concentration rises (indicating decreased filtration), macula densa signals the afferent arteriole to dilate.
      • Increased blood flow to the glomerulus, raises GFR and restores normal salt levels.

    Consequences of Altered GFR

    • High GFR:
      • Glomerulus filters too fast, tubules cannot reabsorb vital substances from the filtrate efficiently.
    • Low GFR:
      • Insufficient filtration, waste products accumulate, affecting overall health.

    Extrinsic Controls of GFR

    • Extrinsic controls primarily regulate glomerular filtration rate (GFR) to maintain systemic blood pressure
    • The sympathetic nervous system constricts afferent arterioles in response to low blood pressure, decreasing GFR
    • Sympathetic nervous system activation occurs through the baroreceptor reflex
    • Afferent arteriole constriction reduces blood flow to the glomerulus, lowering filtration pressure, and decreasing GFR

    Renin-Angiotensin-Aldosterone (RAA) Mechanism

    • Renin, released from granular cells of the afferent arteriole in response to low blood pressure, initiates the RAA mechanism
    • Renin converts angiotensinogen to angiotensin I
    • Angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II
    • Angiotensin II acts as a powerful vasoconstrictor, increasing systemic blood pressure
    • Angiotensin II also stimulates the adrenal cortex to release aldosterone
    • Aldosterone increases sodium and water reabsorption in the kidneys, further elevating blood volume and pressure

    Tubular Reabsorption

    • Most tubular reabsorption occurs in the proximal convoluted tubule (PCT)
    • Tubular reabsorption can occur through the transcellular route (across cell membranes) or paracellular route (between cells)

    ### Baroreceptor Reflex and GFR Regulation

    • The baroreceptor reflex triggers afferent arteriole constriction when blood pressure drops, lowering GFR to help restore blood pressure.

    Angiotensin II and Aldosterone

    • Angiotensin II stimulates the adrenal cortex to release aldosterone, a hormone that increases sodium and water reabsorption in the kidneys, ultimately raising blood volume.

    Angiotensin II and Blood Pressure

    • Angiotensin II causes vasoconstriction of systemic arterioles, which increases blood pressure.

    Systemic Blood Pressure and Kidney Response

    • When systemic blood pressure drops significantly, sympathetic stimulation releases norepinephrine, leading to afferent arteriole constriction.

    Angiotensin II and Blood Volume

    • Angiotensin II increases blood volume by stimulating aldosterone to promote sodium and water reabsorption in the kidneys.

    Renin Release

    • Renin is released from the granular cells of the afferent arteriole in response to decreased systemic blood pressure.

    Tubuloglomerular Feedback

    • The tubuloglomerular feedback mechanism directly links the rate of glomerular filtration to the concentration of salt in the tubule fluid.

    Kidney Response to Low Blood Pressure

    • When systemic blood pressure falls, renin is released to activate the renin-angiotensin-aldosterone mechanism.

    Tubular Reabsorption

    • Most of the content in the filtrate is reclaimed back into the blood through tubular reabsorption.

    Aldosterone and Kidney Action

    • Aldosterone's primary action in the kidneys is to increase sodium and water reabsorption, raising blood volume.

    Reabsorption in the nephron

    • Reabsorption occurs when substances move from the renal tubule back into the bloodstream.
    • The transcellular route involves movement across the tubular epithelial cell membranes.
    • The paracellular route involves movement between the epithelial cells through tight junctions.
    • The proximal convoluted tubule (PCT) reabsorbs most of the water, electrolytes, glucose, and amino acids.
    • The PCT reabsorbs 65% of sodium ions and water.
    • The descending limb of the loop of Henle is permeable to water but not to solutes.
    • The ascending limb of the loop of Henle is impermeable to water but reabsorbs sodium, chloride, potassium, magnesium, and calcium.
    • The distal convoluted tubule (DCT) reabsorbs sodium, chloride, and calcium.
    • The collecting duct reabsorbs sodium, chloride, potassium, bicarbonate, water, and urea.
    • The apical membrane faces the tubular lumen and facilitates transport into the cell.
    • The basolateral membrane faces the interstitial fluid and facilitates transport out of the cell.
    • The peritubular capillaries are located in the interstitial space and play a role in reabsorption.

    Hormonal Control of Tubular Reabsorption and Secretion

    • Antidiuretic Hormone (ADH): ADH increases water reabsorption in the collecting ducts by making the cells more permeable to water. This reduces urine output and helps to maintain blood volume and pressure.

    • Aldosterone: Aldosterone, secreted by the adrenal cortex, increases sodium reabsorption in the distal convoluted tubule (DCT) and collecting ducts. This directly leads to water reabsorption, helping to maintain blood volume and pressure. Aldosterone also promotes potassium secretion into the filtrate.

    • Atrial Natriuretic Peptide (ANP): ANP, secreted by the heart, has the opposite effect of aldosterone. It increases sodium and water excretion, reducing blood volume and pressure.

    • Tubular Secretion: This process removes waste products, drugs, and metabolites from the peritubular capillaries and secretes them into the filtrate.

    • Secretion and Blood pH: Tubular secretion helps maintain blood pH by secreting excess hydrogen ions (H+) into the filtrate, generating bicarbonate ions (HCO3-), which act as a buffer to neutralize excess acid in the blood.

    • Potassium Secretion: Aldosterone plays a crucial role in regulating potassium levels by increasing its secretion in the DCT and collecting ducts.

    • Collecting Duct and Water Permeability: ADH increases the permeability of the collecting duct cells to water, enhancing reabsorption and reducing urine output.

    Function of the Counter Current Multiplier

    • The counter current multiplier is a system in the kidney that helps to concentrate urine.
    • It involves the descending limb and ascending limb of the Loop of Henle.
    • The multiplier is key for establishing and maintaining the medullary osmotic gradient.

    Counter Current Multiplier: The Loop of Henle

    • The ascending limb is impermeable to water, but actively transports salts out.
    • This concentrates the filtrate in the descending limb.
    • As the filtrate becomes more concentrated, water moves out of the descending limb.
    • The descending limb is permeable to water, and a water potential gradient develops.
    • As concentrated filtrate flows into the ascending limb, more salts are pumped out, further increasing the medullary gradient, and drawing more water from the descending limb.

    The Counter Current Exchanger: Vasa Recta

    • The vasa recta is a specialized capillary bed in the medulla, which maintains the medullary osmotic gradient.
    • It prevents the rapid removal of salts from the interstitial fluid.
    • The vasa recta acts as a counter current exchanger. This means as blood flows through the descending portion of the vasa recta, it loses water and gains salts.
    • Then, as the blood flows through the ascending portion of the vasa recta, it gains water and loses salts, maintaining the osmotic gradient.

    Urea Recycling

    • Urea is actively reabsorbed in the collecting duct.
    • Urea diffuses from the tubule fluid into the medullary interstitium, and then back into the thin ascending limb.
    • This process helps to maintain the medullary osmotic gradient.
    • ADH (Antidiuretic hormone) enhances this process.

    Concentrating Urine: The Role of ADH

    • ADH increases water permeability of the collecting duct.
    • This allows more water to be reabsorbed from the tubule fluid, producing concentrated urine.
    • With ADH, urea is also reabsorbed back into the interstitium, increasing the medullary gradient.

    Osmolality and Fluid Balance

    • Overhydration: decreases extracellular fluid (ECF) osmolality.
    • ADH and Overhydration: decreased ADH release leads to decreased water reabsorption in the collecting duct.
    • Overhydrated Urine: large volume of dilute urine is produced.
    • Dehydration: increases ADH release leading to more water reabsorption in the kidneys.
    • Dehydrated Urine: small volume of concentrated urine.

    Diuretics

    • Diuretics: enhance urinary output.
    • Loop Diuretics: block reabsorption of sodium and chloride in the ascending limb of the loop of Henle.
    • Potassium-Sparing Diuretics: block the action of aldosterone, reducing sodium reabsorption while preserving potassium.

    Blood Vessel Layers

    • Tunica Interna (Intima): innermost layer, composed of endothelium and a basement membrane.
    • Tunica Media: middle layer, made of smooth muscle cells and an external elastic lamina. It regulates vessel diameter through vasoconstriction and vasodilation.
    • Tunica Externa (Adventitia): outermost layer, composed of connective tissue that anchors the vessel to surrounding tissues.
    • Nerves and Vasa Vasorum: are located in the tunica externa and are responsible for providing the blood vessel with its own blood supply.

    Capillary Exchange Mechanisms

    • Primary function of capillary exchange: Moving substances between blood and interstitial fluid.
    • Diffusion is the main process for substances moving down their concentration gradient.
    • Intracellular clefts and fenestrations facilitate the movement of water-soluble substances like glucose and ions.
    • Lipid-soluble substances like oxygen and carbon dioxide can pass directly through endothelial cells.
    • The blood-brain barrier (BBB) has tight junctions between endothelial cells, restricting diffusion of substances.
    • Transcytosis is a process where materials are enveloped in vesicles, enter endothelial cells by endocytosis, and exit by exocytosis.
    • Large proteins and hormones are commonly transported via transcytosis.
    • Bulk flow is a passive process based on a pressure gradient, regulating the volume of blood and interstitial fluid.
    • Filtration moves substances from capillaries into interstitial fluid, while reabsorption moves substances from interstitial fluid into capillaries.

    Venous Return

    • Venous return is the volume of blood flowing back to the heart through the systemic veins.
    • The skeletal muscle pump plays a crucial role in propelling blood towards the heart.
    • Veins contain valves that prevent backflow of blood.
    • When skeletal muscles contract, they squeeze veins, increasing pressure and forcing blood towards the heart.
    • The proximal valve opens as pressure rises, allowing blood to flow upwards, while the distal valve closes to prevent backflow.
    • During muscle relaxation, the distal valve opens due to higher pressure in the relaxed muscle, while the proximal valve closes to prevent backflow.
    • The respiratory pump is another mechanism that assists venous return. It utilizes pressure changes during breathing to facilitate blood flow.
    • Inhalation decreases thoracic pressure and increases abdominal pressure, creating a pressure gradient that drives blood from abdominal veins towards the thoracic veins.
    • Valves within veins prevent backflow during exhalation, as thoracic pressure increases.
    • The skeletal muscle pump and venous valves work together to ensure efficient blood flow back to the heart.

    Cardiovascular Center (CVC)

    • The CVC center is responsible for regulating blood pressure and blood flow.
    • It receives input from higher brain regions, baroreceptors, and chemoreceptors.
    • The CVC center sends output via the sympathetic and parasympathetic nervous systems.

    Sensory Input to the CVC Center

    • Baroreceptors: Monitor blood pressure and send input to the CVC center.
    • Chemoreceptors: Monitor blood acidity and CO2 levels, sending input.
    • Higher Brain Regions: Cerebral cortex, limbic system, and hypothalamus.

    Output from the CVC Center

    • Parasympathetic nervous system (vagus nerve) decreases heart rate.
    • Sympathetic nervous system increases heart rate and contractility (cardiac accelerator nerves).
    • Sympathetic nervous system constricts blood vessels (vasomotor nerves).

    Baroreceptors and Blood Pressure Regulation

    • Baroreceptors are sensory receptors that monitor changes in pressure and stretch in the walls of blood vessels. They are essential for regulating blood pressure.
    • Carotid Sinus: Located in the left and right carotid arteries. Contains baroreceptors that monitor blood pressure to the brain.
    • Aortic Arch: Contains baroreceptors that monitor systemic blood pressure.
    • Carotid Sinus Reflex: Activated by blood pressure stretching the carotid sinus. Impulses are transmitted to the cardiovascular center (CVC) via the glossopharyngeal nerve (IX).
    • Aortic Reflex: Activated by changes in pressure in the aortic arch. Impulses are transmitted to the CVC via the vagus nerve (X).
    • CVC (Cardiovascular Center): Located in the medulla oblongata of the brainstem. Receives input from baroreceptors and controls heart rate and blood vessel diameter.
    • Increased Blood Pressure: Baroreceptors detect the increase and send signals to the CVC. The CVC then activates the parasympathetic nervous system via the vagus nerve to lower blood pressure (reducing heart rate and vasodilating blood vessels).
    • Decreased Blood Pressure: Baroreceptors detect the decrease and send signals to the CVC. The CVC activates the sympathetic nervous system to increase blood pressure (increasing heart rate and vasoconstricting blood vessels).
    • The carotid sinus reflex is primarily responsible for maintaining blood flow to the brain.
    • The aortic reflex is primarily responsible for regulating systemic blood pressure.

    Baroreceptors and Blood Pressure Regulation

    • Baroreceptors are specialized sensory receptors located in the carotid sinus and aortic arch that detect changes in blood pressure.
    • When blood pressure decreases, baroreceptors become less stretched and send fewer impulses to the cardiovascular center (CVC) in the brainstem.
    • Decreased impulses from baroreceptors trigger the CVC to increase sympathetic activity, leading to:
      • Increased heart rate and cardiac output
      • Vasoconstriction: narrowing of blood vessels, increasing resistance to blood flow
    • Increased sympathetic activity raises blood pressure.
    • When blood pressure rises, baroreceptors become more stretched and send more impulses to the CVC.
    • The increased impulses stimulate parasympathetic activity, leading to:
      • Decreased heart rate and cardiac output
      • Vasodilation: widening of blood vessels, reducing resistance to blood flow
    • Increased parasympathetic activity decreases blood pressure.

    Chemoreceptor Role in Blood Pressure Regulation

    • Chemoreceptors are located in the carotid bodies and aortic bodies, near baroreceptors, and are sensitive to chemical changes in blood.
    • They monitor blood oxygen (O2), hydrogen ion (H+) concentration (acidity), and carbon dioxide (CO2) levels.
    • When chemoreceptors detect low O2 (hypoxia), high H+ (acidosis), or high CO2 (hypercapnia), they send impulses to the CVC.
    • These impulses stimulate sympathetic activity, leading to:
      • Vasoconstriction: increasing resistance to blood flow
      • Increased heart rate and cardiac output
    • This response aims to increase blood pressure and improve oxygen delivery to tissues.
    • Vasodilation decreases blood pressure by reducing resistance to blood flow.

    Summary of Key Points

    • Baroreceptors regulate blood pressure by adjusting heart rate and vascular resistance.
    • Chemoreceptors monitor blood chemistry and initiate sympathetic activity to improve blood pressure and oxygen delivery in response to low oxygen, high acidity, or high CO2.

    Baroreceptors and Blood Pressure Regulation

    • Baroreceptors are stretch receptors located in the carotid sinus and aortic arch.
    • They detect changes in blood pressure by monitoring the stretch of the vessel walls.
    • When blood pressure decreases, baroreceptors become less stretched and send fewer impulses to the cardiovascular center (CVC) in the brainstem.
    • When blood pressure increases, baroreceptors become more stretched and send more impulses to the CVC.
    • The CVC responds to these signals by adjusting sympathetic and parasympathetic activity to regulate blood pressure.

    ### Cardiovascular Center and Blood Pressure Regulation

    • The CVC is the control center for blood pressure regulation, located in the medulla oblongata of the brainstem.
    • In response to decreased blood pressure, the CVC increases sympathetic activity and decreases parasympathetic activity.
    • Increased sympathetic activity leads to:
      • Increased heart rate (tachycardia)
      • Increased contractility of the heart
      • Vasoconstriction (narrowing of blood vessels)
    • These changes increase cardiac output and peripheral resistance, raising blood pressure.
    • In response to increased blood pressure, the CVC increases parasympathetic activity and decreases sympathetic activity.
    • Increased parasympathetic activity leads to:
      • Decreased heart rate (bradycardia)
      • Vasodilation (widening of blood vessels)
    • These changes decrease cardiac output and peripheral resistance, lowering blood pressure.

    Chemoreceptors and Blood Pressure

    • Chemoreceptors are sensory receptors sensitive to chemical changes.
    • They are located in the carotid bodies and aortic bodies, near the baroreceptors.
    • They monitor blood oxygen (O2), carbon dioxide (CO2), and hydrogen ion (H+) levels.
    • When chemoreceptors detect low O2 (hypoxia), high CO2 (hypercapnia), or high H+ (acidosis), they send signals to the CVC to increase sympathetic activity.
    • Increased sympathetic activity results in vasoconstriction and increased heart rate, leading to increased blood pressure.

    Vasodilation and Blood Pressure

    • Vasodilation is the widening of blood vessels.
    • It is usually triggered by decreased sympathetic activity or parasympathetic activity.
    • Vasodilation reduces peripheral resistance and decreases blood pressure.

    Autoregulation of Blood Pressure

    • Autoregulation is the ability of tissues to automatically adjust blood flow based on their needs.
    • This process is influenced by physical changes, such as warming and cooling, and chemical signals.

    The Cardiac Cycle

    • The sinoatrial (SA) node is the heart's natural pacemaker, initiating action potentials that trigger the cardiac cycle.
    • During rapid filling, the atrioventricular (AV) valves open, allowing blood to flow rapidly into the ventricles.
    • Isovolumetric contraction occurs when all heart valves are closed and intraventricular pressure rises.
    • Isovolumetric relaxation occurs at the end of ventricular systole when all valves are closed.

    Spread of Excitation in the Heart

    • Purkinje fibers are specialized cardiac muscle cells that rapidly distribute the action potential throughout the ventricles, ensuring coordinated contraction.

    The Autonomic Nervous System

    • The parasympathetic nervous system is responsible for slowing the heart rate, via the release of acetylcholine at M2 muscarinic receptors.
    • The sympathetic nervous system primarily releases noradrenaline (norepinephrine), increasing heart rate, force of contraction, and blood pressure.
    • Adrenaline, released by the adrenal medulla, also enhances sympathetic effects.

    Blood Flow Regulation

    • Arterioles offer the highest resistance to blood flow, causing a significant pressure drop.
    • Vasodilation decreases resistance, increasing blood flow and lowering blood pressure.
    • The myogenic response is the automatic contraction of smooth muscle in blood vessels, responding to pressure changes.

    The Renin-Angiotensin-Aldosterone System (RAAS)

    • RAAS is triggered by low blood flow to the kidneys.
    • RAAS helps regulate blood pressure and fluid balance.

    The Cardiac Cycle

    • Ventricular Systole: Blood is ejected from the ventricles into the arteries
    • Ventricular Diastole: Ventricles relax, and all valves close
    • Isovolumetric Relaxation: The ventricles relax, and all valves are closed
    • Atrial Systole: Atria contract after the rapid filling phase of the ventricles
    • The AV node delays the action potential to allow atrial contraction before ventricular contraction

    Hormones Involved in Blood Pressure Regulation

    • Antidiuretic Hormone (ADH): Promotes water reabsorption in the kidneys, increasing blood pressure
    • Aldosterone: Promotes sodium retention, indirectly increasing blood pressure
    • Atrial Natriuretic Peptide (ANP): Decreases blood pressure by promoting vasodilation and excretion of salt and water

    Baroreceptors & Chemoreceptors

    • Baroreceptors detect changes in blood pressure: High blood pressure increases baroreceptor activity, sending more impulses to the cardiovascular center
    • Chemoreceptors detect changes in blood oxygen and carbon dioxide levels: Low oxygen levels (hypoxia) stimulate the sympathetic nervous system, increasing heart rate and vasoconstriction

    The Sympathetic & Parasympathetic Nervous System

    • The sympathetic nervous system releases noradrenaline, increasing heart rate and blood pressure
    • The parasympathetic nervous system releases acetylcholine, decreasing heart rate and blood pressure

    Arteries

    • Arteries maintain high pressure due to their thick, muscular walls and connection to high-resistance arterioles.

    Brain Areas

    • Left Primary Motor Cortex: Initiates voluntary movement of the right thumb.
    • Medulla: Responsible for the crossover of upper motor neurons (UMN) to the contralateral side of the body.
    • Spinal Cord Anterior Horn: Location where upper motor neurons synapse with lower motor neurons.

    Motor Neuron Pathways

    • Upper Motor Neuron (UMN) Pathway:
    • UMNs originate in the left motor cortex and travel through the internal capsule, midbrain, brainstem, and cross over in the medulla.
    • UMNs are contained in the lateral corticospinal tract as they descend through the spinal cord.
    • Lower Motor Neuron (LMN) Pathway:
    • LMNs receive signals from UMNs in the anterior horn of the spinal cord and directly innervate muscles to initiate movement.

    Chemoreceptor Control of Breathing

    • Aortic and Carotid Bodies: Located in the aorta and carotid arteries and contain peripheral chemoreceptors sensitive to changes in blood oxygen levels, CO2 levels, and pH.
    • Chemoreceptor Response:
    • Increased arterial partial pressure of CO2 and decreased blood pH triggers chemoreceptors to activate.
    • Chemoreceptors send signals to the respiratory center in the medulla oblongata.
    • Medulla Oblongata Respiratory Center:
    • Receives signals from chemoreceptors and initiates an increase in ventilation rate.
    • Sends signals through spinal cord motor neurons to activate respiratory muscles.
    • Respiratory Muscles:
    • Diaphragm and intercostal muscles are responsible for breathing.
    • Increased ventilation leads to a decrease in arterial partial pressure of CO2 and normalization of blood pH.

    Upper Motor Neurons (UMN)

    • Initiate voluntary motor movements from the brain to the spinal cord

    Lower Motor Neurons (LMN)

    • Directly target and activate muscles responsible for movement
    • Example: LMNs in the spinal cord control the muscles of the thumb.

    Respiratory Control

    • Medulla oblongata sends motor neuron signals to the respiratory muscles, increasing ventilation when needed
    • High arterial partial pressure of CO2 stimulates increased ventilation to expel CO2 and normalize pH
    • Chemoreceptors in the carotid and aortic bodies detect high CO2 levels in the blood

    Cardiac Cycle

    • SA node acts as the pacemaker of the heart, generating action potentials
    • During isovolumetric contraction, the ventricles contract, and all valves are closed. Pressure inside the ventricles increases until it exceeds the pressure in the arteries, forcing the semilunar valves open
    • Ventricular contraction causes increased intraventricular pressure which closes the AV valves
    • Increased plasma CO2 levels stimulate chemoreceptors in the medulla oblongata, increasing ventilation

    Blood pH

    • High CO2 concentration in the blood decreases blood pH, leading to acidosis.
    • Increased ventilation helps to remove CO2 from the blood, raising the pH back to normal.

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    Test your knowledge on the HPT axis in this quiz! The hypothalamus, pituitary gland, and thyroid work together to regulate thyroid hormones T3 and T4. Understand the feedback mechanisms and the importance of hormonal balance in the body.

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