Endocrine System Summary Notes PDF

Bioscience 1 The Endocrine System Summary notes Prescribed text: Marieb, E.N., & Hoehn, K. (2019). H...

Bioscience 1 The Endocrine System Summary notes Prescribed text: Marieb, E.N., & Hoehn, K. (2019). Human anatomy & physiology. Global edition (11th ed.). Pearson. Chapter 16. Endocrine System  A complex of glands, that are not anatomically connected but are interrelated as an organ system that secrete hormones.  Endocrine glands are ductless glands.  Response slower but longer lasting than nervous system.  Influences metabolic activities or secretion of other hormones. (Marieb & Hoehn, 2019, Figure 16.1) Bioscience 1 Summary Notes- The Endocrine System Page 1 of 19  Endocrine glands through the use of hormones controls and integrates: – Reproduction – Growth and development – Maintenance of electrolytes, water, and nutrient balance of blood – Regulation of cellular metabolism and energy balance – Mobilisation of body defenses Hormones- Chemical Messengers Hormones: long-distance chemical signals; travel in blood or lymph to target tissues Hormones are classified as either amino acid based or steroids. 1. Amino acid based: Majority of hormones. Made from amino acids. examples: thyroid hormones, insulin and glucagon. Are water soluble and unable to cross the plasma membrane. 2. Steroids: Synthesised from cholesterol. Only gonadal and adrenocortical hormones are steroid based hormones. Examples: aldosterone, cortisol, testosterone and estrogen. Are lipid soluble and able to cross the plasma membrane. Mechanisms of Hormone Action All hormones circulate systemically to all tissues, BUT only certain cells called target cells, with receptors for that hormone are affected. The response will be to alter target cell activity (increasing or decreasing cell processes) Hormones alter target cell activity by: (mitosis, secretory, deactivate, enzymes, channels, permeability ) – Alter plasma membrane ………………………………… and/or membrane potential by opening or closing ion ……………………. – Stimulate synthesis of …………………………..or other proteins – Activate or ………………………………enzymes – Induce ……………………………. activity – Stimulate …………………………………. Bioscience 1 Summary Notes- The Endocrine System Page 2 of 19  How Hormones communicate with target cells? 1. Water-soluble hormones (all amino acid–based hormones 2. Lipid-soluble hormones (steroid and thyroid hormones) except thyroid hormone) (Marieb & Hoehn, 2019, Figure 16.2) - Can enter cell (Marieb & Hoehn, 2019, figure 16.3) - Cannot enter cell - Hormones diffuse through plasma membrane and enter the - Act on receptors located in plasma membrane of specific cell. (See diagram below) target cells which transmit message to inside the cell. - Act on intracellular receptors that directly activate genes - Cascade effect takes place inside target cell to trigger responses by cell Bioscience 1 Summary Notes- The Endocrine System Page 3 of 19 There are three types of stimuli that cause hormone release. Endocrine gland stimulated to synthesise and release hormones in response to: a. Humoral Stimuli (Marieb & Hoehn, 2019, figure 16.4a) Changing blood levels of ions and nutrients directly stimulate secretion of hormones  Example: Calcium ions (Ca2+) concentration in blood Decreasing blood Ca2+ concentration stimulates parathyroid glands to secrete parathyroid hormone (PTH) PTH causes Ca2+ concentrations to rise to normal range and stimulus is removed  Homeostasis is restored. Negative feed-back system is turned off. b. Neural Stimuli (Marieb & Hoehn, 2019, figure 16.4b) Nerve fibers stimulate hormone release  Stress is an example. In response to a perceived threat, the sympathetic nervous system fibers stimulate adrenal medulla to secrete Epinephrine (Adrenaline) and Norepineprine (Noradrenaline) – Fight and Flight Response c. Hormonal Stimuli (Marieb & Hoehn, 2019, figure 16.4c) Hormones stimulate other endocrine organs to release their hormones  Hypothalamic hormones stimulate release of most anterior pituitary hormones i.e. TRH  Example: Hypothalamus releases Growth Hormone Releasing Hormone (GHRH) which acts on the Anterior Pituitary – the Anterior Pituitary then secretes Growth Hormone (GH) (Marieb & Hoehn, 2019, figure 16.5). Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from final target organs inhibit release of anterior pituitary hormones. Bioscience 1 Summary Notes- The Endocrine System Page 4 of 19 Three types of stimuli that cause hormone release. (Marieb & Hoehn, 2019, figure 16.4). Bioscience 1 Summary Notes- The Endocrine System Page 5 of 19 MAJOR ENDOCRINE GLANDS Hypothalamus – located within the brain (Marieb & Hoehn, 2019, Focus Figure16.1, page 642). - Hypothalamus receives input from various regions of the brain, internal organs and the retina and will secrete hormones accordingly. - Hypothalamic hormones play important roles in all aspects of growth, development, metabolism and homeostasis. Hypothalamic – Regulating Hormones - All act on anterior pituitary gland - 4 releasing hormones & 2 inhibiting hormones 1. Corticotropin Releasing Hormone (CRH) – stimulates the Anterior Pituitary to secrete Adrenocorticotropic Hormone (ACTH) 2. Thyrotropin Releasing Hormone (TRH)- stimulates the Anterior Pituitary to secrete Thyroid Stimulating Hormone (TSH) 3. Gonadotropin Releasing Hormone (GnRH) - stimulates the Anterior Pituitary to secrete Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH). 4. Growth Hormone Releasing Hormone (GHRH) - stimulates the Anterior Pituitary to secrete Growth Hormone (GH) 5. Growth Hormone Inhibiting Hormone (GHIH) – inhibits the release of Growth Hormone (GH) from the Anterior Pituitary. 6. Prolactin Inhibiting Hormone (PIH or dopamine) – a decrease in PIH causes release of Prolactin (PL) from the Anterior Pituitary Bioscience 1 Summary Notes- The Endocrine System Page 6 of 19  Hypothalamic – Pituitary Relationships Axons extend from the hypothalamus through the infundibulum (stalk of the pituitary gland) into the Posterior Pituitary lobe/gland (neurohypophysis) (Marieb & Hoehn, 2019, Focus Figure16.1). - Hypothalamus produces two hormones - Oxytocin and Antidiuretic hormone (ADH). - The axons transport the hormones from the hypothalamus to the posterior pituitary gland where they are stored and released on need. - Hypothalamic hormones travel in the blood stream through the infundibulum to the Anterior Pituitary lobe/gland where they stimulate (releasing) or inhibit secretion of Anterior pituitary hormones Bioscience 1 Summary Notes- The Endocrine System Page 7 of 19 Posterior Pituitary Hormones (Marieb & Hoehn, 2019 Table 16.3)  Antidiuretic Hormone (ADH or Vasopressin) (Marieb & Hoehn, 2019, page 645 When blood becomes dehydrated (too concentrated) causing decreased blood volume and BP, ADH is released which: – Targets kidney tubules  reabsorb more water back into blood to increase blood volume & BP – Regulates water balance by inhibiting urine formation (reduced urine output) Oxytocin - Read page 644 – Released during childbirth – Acts on uterus to cause uterine contraction – Hormonal trigger for milk ejection during breast feeding – Positive feedback mechanism Anterior Pituitary Hormones (Marieb & Hoehn, 2019 Table 16.3) a) Growth Hormone (GH, or Somatotropin) (Marieb & Hoehn, 2019, figure 16.5)- Read page 647 Mediates growth via growth-promoting proteins – insulin-like growth factors (IGFs) Stimulates: – Promotes growth and development – Major targets - bone and skeletal muscle – Formation of collagen and deposition of bone matrix Direct actions on metabolism – Increases blood levels of fatty acids; encourages use of fatty acids for fuel – Decreases rate of glucose uptake and metabolism (conserving glucose)  Glycogen breakdown and Glucose release to blood Peak levels of GH occur during evening sleep. GH levels peak during adolescence and then declines with age. Infants and children have highest levels of GH due to promotion of growth needed in the individual. Bioscience 1 Summary Notes- The Endocrine System Page 8 of 19  GH release chiefly regulated by 2 hypothalamic hormones: – Growth hormone–releasing hormone (GHRH)- stimulates the Anterior Pituitary to secrete Growth Hormone (GH) – Growth hormone–inhibiting hormone (GHIH) (somatostatin) - inhibits the release of (GH) from the Anterior Pituitary. b) Thyroid-stimulating Hormone-TSH (Thyrotropin)- Read page 648 Target tissue is Thyroid gland Stimulates normal development and secretory activity of thyroid gland (release of thyroid hormones) Release triggered by thyrotropin-releasing hormone (TRH) from hypothalamus Rising blood levels of thyroid hormones inhibits TSH release c) Adrenocorticotropic Hormone- ACTH (Corticotropin) Read page 648 Stimulates adrenal cortex to release corticosteroids Regulation of ACTH release – Triggered by hypothalamic corticotropin-releasing hormone (CRH) in daily rhythm – Internal and external factors such as fever, hypoglycemia, and stressors can alter release of CRH d) Gonadotropins - Follicle-stimulating hormone (FSH) and luteinising hormone (LH) Read page 648 FSH stimulates gamete (egg or sperm) production LH promotes production of gonadal hormones Regulation of gonadotropin release: – Triggered by gonadotropin-releasing hormone (GnRH) from hypothalamus during and after puberty – Suppressed by gonadal hormones (feedback) Absent from the blood in prepubertal boys and girls Release of hormones activated at puberty Bioscience 1 Summary Notes- The Endocrine System Page 9 of 19 e) Prolactin (PRL) Read page 648 Stimulates milk production Regulation of release: – Primarily controlled by prolactin-inhibiting hormone (PIH) (dopamine) – Decrease in PIH leads to increased Prolactin release. Prolactin levels rise and fall in rhythm with estrogen levels. Brief elevated levels just before menstruation accounts for slight swelling and tenderness of breasts during this time. Blood levels rise dramatically toward end of pregnancy and milk production follows Suckling stimulates Prolactin release and promotes continued milk production. Works in conjunction with oxytocin (stimulates milk ejection) during breast feeding. Thyroid Gland Read page 649 Located anterior to the trachea in the neck. Release of thyroid hormones T3 (triiodothyronine) and T4(thyroxine) Gland composed of repeated follicles filled with the glycoprotein thyroglobulin Follicles filled with colloid (fluid with thyroglobulin + iodine) and is precursor of thyroid hormones Thyroglobulin + iodine combines to form the thyroid hormones which are then released into the blood stream Dietary supply of iodine is needed for thyroid hormone production Parafollicular cells produce the hormone calcitonin in response to elevated calcium blood levels Thyroid Hormone (TH) – Major metabolic hormone which affects nearly every cell in the body (Marieb & Hoehn, 2019, Table 16.4 on page 650) (blood pressure, iodide, skeletal, tissue growth, metabolic rate ) Increases ………………………………………… and heat production (calorigenic effect) Regulation of ……………………………………. and development – Development of …………………………………. and nervous systems Bioscience 1 Summary Notes- The Endocrine System Page 10 of 19  – Reproductive capabilities Maintenance of …………………………………………….. Dietary....................................... is required for production of T 3 and T4. Regulation of TH Read page 652 Both T3 and T4 bind to target receptors, but T3 is ten times more active than T4 Peripheral tissues convert T4 to T3 Negative feedback regulation of TH release (Marieb & Hoehn, 2019, Figure 16.7 on page 648) – Release is stimulated by TSH (from anterior pituitary) and TRH (from hypothalamus) – Low blood levels of TH triggers release of TRH (by hypothalamus) which stimulates release of TSH (by anterior pituitary). TSH acts on thyroid gland to stimulate TH synthesis and release into blood stream. – Rising TH levels provide negative feedback on hypothalamus and anterior pituitary to inhibit release of TSH Calcitonin Released in response to high blood Calcium ion (Ca2+) levels Produced by parafollicular (C) cells located in the thyroid gland At higher than normal doses – Inhibits osteoclast (bone absorbing cell) activity and release of Ca2+ from bone matrix in the blood stream – Stimulates Ca2+ uptake from blood stream and stimulates osteoblast (bone forming cell) activity to incorporate into bone matrix Antagonist to parathyroid hormone (PTH) Bioscience 1 Summary Notes- The Endocrine System Page 11 of 19 Parathyroid Glands Read page 653 (Marieb & Hoehn, 2019 Figures 16.11 & 16.12) Four to eight tiny glands embedded in posterior aspect of thyroid gland Is a separate gland to thyroid gland Cells secrete parathyroid hormone (PTH) PTH - most important hormone in Ca2+ homeostasis Secretes PTH at low Ca2+ blood levels PTH Actions: see diagram to left – Stimulates osteoclasts (bone absorbing cells) to digest bone matrix and release Ca2+ into blood – Enhances reabsorption of Ca2+ and secretion of phosphate by kidneys – Promotes activation of vitamin D (by kidneys); increasing absorption of Ca2+ in small intestines Negative feedback control: rising Ca2+ in blood inhibits PTH release. Bioscience 1 Summary Notes- The Endocrine System Page 12 of 19 Adrenal (Suprarenal) Glands - Gland located at superior end on kidneys - Structurally and functionally are two glands in one. - Consists of inner adrenal medulla and outer adrenal cortex. - Medulla and cortex act as separate glands and secrete different hormones a) Adrenal Medulla Read page 659 nervous tissue; part of sympathetic nervous system secrete epinephrine (80%) called adrenaline, and norepinephrine (20%) called noradrenaline, in response to stress Released when there is a short-term stress to the body to sustain the fight or flight response Effects: – Vasoconstriction – Increased heart rate---elevates BP – Increased blood glucose levels – Blood diverted away temporarily from nonessential organs to brain, heart, and skeletal muscle – Brochodilation Epinephrine stimulates metabolic activities, bronchial dilation, and blood flow to skeletal muscles and heart Norepinephrine influences peripheral vasoconstriction and blood pressure b) Adrenal Cortex Read page 655 three layers of glandular tissue. 3 different hormones produced. 1. mineralocorticoids 2. glucocorticoids 3. gonadocorticoids Bioscience 1 Summary Notes- The Endocrine System Page 13 of 19  1. Mineralocorticoids Read page 655 Regulates electrolytes (primarily Sodium ions (Na + ) and Potassium ions ( K+) in extracellular fluid (ECF) Importance of Na+: affects ECF volume, blood volume, blood pressure 2. Glucocorticoids Importance (Marieb of K+: sets Resting membrane potential & Hoehn, 2019, (RMP) table 16.5 of cells. on page 658) Keep blood glucose levels relatively constant Aldosterone Maintain most potent blood pressure by increasing mineralocorticoid secreted action oflayer in this (Marieb & Hoehn, 2019, figure 16.14) vasoconstrictors - Decreasing blood volume Cortisol - Onlyand oneBPin triggers aldosterone significant amounts in release humans - Stimulates Na reabsorption and water retention by kidneys and + Cortisone elimination of K+ to increase blood volume and BP Corticosterone Cortisol Mechanisms of Aldosterone Secretion see diagram on left Prime metabolic effect is gluconeogenesis—formation of Primary regulator: Renin-angiotensin-aldosterone glucose from fats and proteins mechanism: – Promotes rises in blood glucose, fatty acids, and decreased blood pressure and/or blood volume stimulates amino acids kidneys to release renin  triggers formation of angiotensin Released in response to ACTH (from anterior pituitary) II,  stimulates aldosterone release  causes increased Na+ Stress triggers release of cortisol (that triggers glucose to and water reabsorption and K+ secretion be released into the blood to prepare for stress) increased K+ in blood directly influences release of cortisol enhances the sympathetic nervous system (fight or aldosterone flight response to stress) Minor influences: Enhances vasoconstriction  rise in blood pressure to ACTH: causes small increases of aldosterone during stress quickly distribute nutrients to cells Atrial natriuretic peptide (ANP): released when there is an Prolonged stress can cause excessive amounts of cotisol to be released and cause depressed inflammatory response and increase in blood volume/BP immune system. blocks renin and aldosterone secretion to decrease blood Glucocorticoid drugs are often used to control the symptoms of many chronic inflammatory disorders as it acts as an anti- pressure inflammatory. Bioscience 1 Summary Notes- The Endocrine System Page 14 of 19 3. Gonadocorticoids (Sex Hormones) Most weak androgens (male sex hormones) converted to testosterone in tissue cells, some to oestrogen May contribute to – Onset of puberty – Appearance of secondary sex characteristics – Sex drive in women – Oestrogen in postmenopausal women Stress and the Adrenal gland- See Focus Figure 16.2 Adrenal medulla secretes Adrenal cortex secretes epinephrine and cortisol and aldosterone norepinephrine (via the (via stimulation from sympathetic nervous ACTH from anterior system) in response to pituitary) in response to short term stress (fight or prolonged term stress flight response) Bioscience 1 Summary Notes- The Endocrine System Page 15 of 19 Pineal Gland Read page 659 Small gland located in brain Secretes melatonin Melatonin may affect – Timing of sexual maturation and puberty – Influences sleeping patterns – Melatonin levels vary during the daily cycle. Peak levels during night which make you drowsy. Lowest levels at noon. Pancreas Read page 662 (Marieb & Hoehn, 2019, Figure 16.17) Endocrine cells present in pancreas as specialised clusters called Pancreatic Islets of Langerhans Islets of Langerhans contain cells that secrete hormones that regulate blood glucose levels Alpha () cells produce glucagon Beta () cells produce insulin Glucagon Major target—liver Secreted at low blood glucose levels Causes increased blood glucose levels Effects: – Glycogenolysis—breakdown of glycogen to glucose – Gluconeogenesis—synthesis of glucose from noncarbohydrates (proteins & lipids) – Release of glucose into blood by the liver to elevate blood glucose levels Insulin  Secreted at high blood glucose levels  Lowers blood glucose levels by: – Enhances uptake of glucose into fat and muscle cells Bioscience 1 Summary – Inhibits Notes- The glycogenolysis andEndocrine System Page 16 of 19 gluconeogenesis Testes, Ovaries and Placenta Read page 666  Ovaries produce oestrogen and progesterone – Oestrogen Maturation of female reproductive organs Appearance of secondary sexual characteristics With progesterone, causes breast development and cyclic changes in uterine lining (and menstruation) – Progesterone – pregnancy maintaining hormone Works with oestrogen to establish and regulate the uterine cycle During pregnancy inhibits uterine motility, prepares the breasts for lactation  Placenta secretes oestrogen, progesterone, and human chorionic gonadotropin (hCG) to maintain pregnancy. – Relaxin also produced by placenta which causes pelvic ligaments and pubic symphysis to relax and widen and become more flexible in preparation for child-birth  Testes- produce testosterone – Initiates maturation of male reproductive organs – Causes appearance of male secondary sexual characteristics and sex drive – Necessary for normal sperm production Bioscience 1 Summary Notes- The Endocrine System Page 17 of 19  – Maintains reproductive organs in functional state Heart (Marieb & Hoehn, 2019, page 666) - Secretes Atrial natriuretic peptide (ANP) in response to high blood pressure and blood volume Target kidneys: inhibits Na+ reabsorption from urine and renin release  decreases blood Na+ concentration,  decreases water reabsorption into blood from urine  decreases blood volume and blood pressure  increased urine output Kidneys (Marieb & Hoehn, 2019, page 666) – Secretes erythropoietin, a hormone that signals to red bone marrow to produce more red blood cells. Skin (Marieb & Hoehn, 2019, page 667) – Production of cholecalciferol, an inactive form of vitamin D when epidermal cells are exposed to UV radiation. – Cholecalciferol enters blood stream where it is modified; by the liver and kidneys; into the active form of vitamin D, called calcitriol. – Vit D required for absorption of calcium into the blood stream from small intestines. – Required for calcium deposits into bone, making bones hard and strong. Endocrine System across the life Span Most endocrine organs operate well until old age Exposure to pesticides, industrial chemicals, arsenic, dioxin, and soil and water pollutants disrupts hormone function Sex hormones, thyroid hormone, and glucocorticoids are vulnerable to the effects of pollutants Interference with glucocorticoids may help explain high cancer rates in certain areas Bioscience 1 Summary Notes- The Endocrine System Page 18 of 19  Ovaries undergo significant changes with age and become unresponsive to gonadotropins; problems associated with oestrogen deficiency occur Testosterone also diminishes with age, but effect is not usually seen until very old age GH levels decline with age - accounts for muscle atrophy with age TH declines with age, contributing to lower basal metabolic rates PTH levels remain fairly constant with age, but lack of estrogen in older women makes them more vulnerable to bone- demineralising effects of PTH Bioscience 1 Summary Notes- The Endocrine System Page 19 of 19