Endocrine System PowerPoint Presentation PDF

Chapter 17 Endocrine system  Overview of Cell Communications Intercellular communication – 100 trillion cells in the human body Organized into four basic tissues Four tissues are organized into the organs of the body It is vital for cells to communicate with each ot...

Chapter 17 Endocrine system  Overview of Cell Communications Intercellular communication – 100 trillion cells in the human body Organized into four basic tissues Four tissues are organized into the organs of the body It is vital for cells to communicate with each other to preserve the functions of each organ and thus maintain body homeostasis. There are six major forms of intercellular communication  Types of Cell Communications – Direct communication mediated by gap junctions pores in cell membrane allow small signaling chemicals to move from cell to cell – Autocrine communication mediated by local hormones (paracrine factors or cytokines) are secreted from the cell that is also the target cells – Paracrine communication mediated by local hormones (paracrine factors or cytokines) are secreted into extracellular fluids to affect nearby target cells Types of Cell Communications cont. – Juxtacrine communication mediated by local hormones (paracrine factors or cytokines) are held on the plasma membrane and the target cell binds or links up to the bound factor. Involved in growth and differentiation. – Synaptic communication mediated by neurotransmitters are released from presynaptic cell (usually a neuron) to travel across gap to bind to a postsynaptic target cell for example, a second neuron or muscle cell – Endocrine communication mediated by hormones secreted into extracellular fluids before entering the blood vessels and travel to affect distant target cells Mechanisms of intercellular communication  Cell Communications Overview Paracrine, autocrine, juxtacrine, synaptic, and endocrine communication requires that the target cells express receptors made of proteins (protein receptors) Receptors binds to the chemical messengers (signals) released from other cells and provide the mechanism whereby the messenger can be detected Binding of the messenger to the receptor activates the receptor and leads to intracellular events that changes the cells activities These changes or events are termed signal transduction 17-6 Endocrine System Components I) Endocrine glands or tissues – produce hormones II) Hormones – chemical messenger secreted into the bloodstream, stimulates response in another tissue or organ III)Target cells – have receptors for the hormone  Endocrine vs. Exocrine Glands Exocrine glands – ducts carry secretion to a surface or organ cavity product is releases onto an epithelial tissue – product has extracellular effects (food digestion) Endocrine glands or tissues – no ducts, release hormones into tissue fluids, hormone inters dense highly permeable capillary networks to distribute hormones – hormones have intracellular effects, alter target cell metabolism  Communication Systems: Nervous System vs. Endocrine System Nature of communication – nervous - both electrical and chemical – endocrine - only chemical Speed and persistence of response – nervous - reacts quickly (1 - 10 msec), stops quickly – endocrine - reacts slowly (hormone release in seconds or days), effect may continue for weeks Adaptation to long-term stimuli – nervous - response declines (adapts quickly) – endocrine - response persists Area of affect – nervous - targeted and specific (one organ) – endocrine - general, widespread effects (many organs)  Nervous and Endocrine Systems Several chemicals function as both hormones and neurotransmitters – NE, cholecystokinin, thyrotropin-releasing hormone, dopamine and ADH Some hormones secreted by neuroendocrine cells (neurons) – oxytocin and catecholamines Both systems with overlapping effects on same target cells – NE and glucagon cause glycogen hydrolysis in liver Systems regulate each other – neurons trigger hormone secretion – hormones stimulate or inhibit neurons  Endocrine Systems Types of cellular functions controlled by the endocrine system – Reproduction – Growth – Development – Activation of body defenses – Salt and water balance – Nutrient balance – Cellular metabolism  Major Endocrine Organs Hypothalamus Pituitary – Adenohypophsis – Neurohypophsis Pineal gland Thyroid gland Parathyroid gland Thymus Adrenal gland – Adrenal cortex – Adrenal medulla Pancreas Ovaries Testes Table 17.2  Hypothalamus location Shaped like a flattened funnel, forms floor and walls of third ventricle  Endocrine Role of the Hypothalamus – 1) Release of hormones that controls anterior pituitary  Endocrine Role of the Hypothalamus cont. Endocrine Role of the Hypothalamus – 2) Produces and controls the releases of oxytocin and ADH from the posterior pituitary – 3) Controls the release of epinephrine and norepinephrine from adrenal medulla Controls parasympathetic vs. sympathetic tone  Pituitary Gland (Hypophysis) Suspended from hypothalamus by stalk (infundibulum) Location and size – housed in sella turcica of sphenoid bone – 1.3 cm diameter Parts of the pituitary gland – Adenohypophysis (anterior pituitary) arises from hypophyseal pouch (outgrowth of pharynx) – Neurohypophysis (posterior pituitary) down growth of hypothalamus – (neural tissue) Embryonic Development  Adenohypophysis Also called anterior pituitary  Hypothalamo-Hypophyseal Portal System Hormones from hypothalamus enter a capillary bed and travel in portal system to exit at the anterior pituitary Hormones secreted by anterior pituitary enter a second capillary bed to join the common circulation  Anterior Pituitary Hormones Principle hormones and target organs shown Axis - refers to way endocrine glands interact Pituitary Hormones - Anterior Lobe Trophic hormones target other endocrine glands – gonadotropins target gonads FSH (follicle stimulating hormone) LH (luteinizing hormone) – TSH (thyroid stimulating hormone) – ACTH (adrenocorticotropic hormone) PRL (prolactin) GH (growth hormone) Hormone Actions: Anterior Lobe FSH (secreted by gonadotrope cells) – stimulates production of egg or sperm cells LH (secreted by gonadotrope cells) – mainly stimulates hormone production females - stimulates ovulation and corpus luteum to secrete progesterone and estrogen males - stimulates interstitial cells of testes to secrete testosterone TSH (secreted by thyrotropes) – stimulates growth of gland and secretion of TH Hormone Actions: Anterior Lobe cont. ACTH or corticotropin (secreted by corticotropes) – regulates response to stress, stimulates adrenal cortex corticosteroids from adrenal cortex regulate glucose, fat and protein metabolism PRL (secreted by lactotropes) – female - milk synthesis after delivery – male -  LH sensitivity, thus  testosterone secretion Released after organism giving a calming effect GH or somatotropin – see next two slides  Growth Hormone Secreted by GH (somatotropes) of anterior pituitary Promotes tissue growth – mitosis and cellular differentiation – stimulates liver to produce IGF-I and II (somatomedins) – (somatomedin release also stimulated by prolactin) protein synthesis –  DNA transciption for  mRNA production, proteins synthesized – enhances amino acid transport into cells,  protein catabolism lipid metabolism – stimulates FFA and glycerol release from adipocytes, protein sparing CHO metabolism – glucose sparing effect = less glucose used for energy Electrolyte balance – promotes Na+, K+, Cl- retention, Ca 2+ absorption  Growth Hormone and Aging Childhood and adolescence – bone, cartilage and muscle growth – stimulates growth at epiphyseal plates Adulthood – increase osteoblastic activity and appositional growth affecting bone thickening and remodeling – blood concentration decrease by age 75 to ¼ of that of adolescent Levels of GH (fluctuates throughout day) – higher during deep sleep, after high protein meals, after vigorous exercise – lower after high CHO meals  Neurohypophysis Also called posterior pituitary  Pituitary Hormones - Posterior Lobe OT (oxytocin) and ADH – produced in hypothalamus – transported by hypothalamo-hypophyseal tract to posterior lobe (stores then releases hormones) Hormone Actions: Posterior Lobe ADH – targets kidneys  water retention, reduce urine – also functions as neurotransmitter Oxytocin – labor contractions, lactation – possible role in sperm transport emotional bonding  Control of Pituitary: Pituitary hormones are not secreted at a constant rate – Example GH highest at night LH, FSH, estrogen varies during the menstrual cycle Timing is regulated by hormones from the hypothalamus and other brain centers connected to the hypothalamus  Control of Anterior lobe of Pituitary: Hypothalamic and Cerebral Control Anterior lobe control – – Results from releasing hormones and inhibiting hormones released from the hypothalamus  Control of Posterior lobe of Pituitary: Hypothalamic and Cerebral Control Posterior lobe control – – Results from neuroendocrine reflexes hormone release in response to nervous system signals – Oxytocin release » Suckling infant stimulates nerve endings hypothalamus posterior lobe oxytocin milk ejection » Oxytocin also release in response to higher brain centers milk ejection reflex can be triggered by a baby's cry  Control of Posterior lobe of Pituitary: Hypothalamic and Cerebral Control cont. Posterior lobe control – – Results from neuroendocrine reflexes hormone release in response to nervous system signals – ADH release » Dehydration increases osmolarity of blood and activates osmoreceptors in the hypothalamus » Osmoreceptors trigger posterior lobe to release ADH » ADH promotes water conservation by the kidneys Pineal Gland location  Pineal Gland Peak secretion ages 1-5; by puberty 75% lower Produces serotonin by day, converts it to melatonin at night May regulate timing of puberty in humans – Removal causes premature sexual maturation Melatonin levels  in seasonal affective disorder (SAD); melatonin levels  by phototherapy – SADs = depression, sleepiness, irritability and carbohydrate craving  Thymus Location: mediastinum, superior to heart Involution after puberty Secretes hormones that regulate development and later activation of T-lymphocytes – thymopoietin thymulin and thymosins  Thyroid Gland Anatomy Largest endocrine gland; high rate of blood flow – arises from root of embryonic tongue Anterior and lateral sides of trachea – two large lobes connected by isthmus Histology of the Thyroid Gland  Thyroid Gland Thyroid follicles – filled with a protein colloid (thyroglobulin) and lined with simple cuboidal epithelial (follicular cells) – Follicular cells secretes two hormones, T3 and T4 thyroid hormone –  body’s metabolic rate and O2 consumption – calorigenic effect -  heat production –  heart rate and contraction strength –  respiratory rate –  activity of the nervous system – stimulates appetite and breakdown CHO, lipids and proteins – stimulates growth of bone, skin, hair, nails, teeth and nervous sytem » Triggers release of growth hormone C cells or parafollicular cells – produce calcitonin that  blood Ca2+ , promotes Ca2+ deposition and bone formation especially in children  Parathyroid Glands PTH release –  blood Ca2+ levels PTH actions – promotes synthesis of calcitriol by kidneys  absorption of Ca2+  urinary excretion of Ca2+  bone resorption  Adrenal Gland Two glands in one Adrenal cortex epithelial in origin Adrenal medulla neural in origin  Adrenal Medulla The medulla is basically a sympathetic ganglion innervated by sympathetic preganglionic fibers – consists of modified neurons called chromaffin cells – stimulation causes release of catecholamines (epinephrine, NE and a little dopamine) Hormonal effect is longer lasting then Epi and NE released from sympathetic nerves – Increases alertness, anxiety, or fear – increases BP, heart rate and air flow – raises metabolic rate inhibits insulin secretion – glucose-sparing effect stimulates gluconeogenesis and glycogenolysis – Inhibits digestion and urine production etc. Stress causes medullary cells to stimulate cortex  Adrenal Cortex Layers – zona glomerulosa (outer) – zona fasciculata (middle) – zona reticularis (inner)  Adrenal Cortex cont. Corticosteroids – mineralocorticoids (zona glomerulosa) control electrolyte balance, aldosterone promotes Na+ retention and K+ excretion – glucocorticoids (zona fasciculata) especially cortisol, stimulates fat and protein catabolism, gluconeogenesis (from a.a.’s and FA’s) and release of fatty acids and glucose into blood – allows the body to deal with stress and heal anti-inflammatory effect becomes immune suppression with long-term use – sex steroids (zona reticularis) androgen (including DHEA which other tissues convert to testosterone) and estrogen (important after menopause)  Adrenal Cortex Hormones – Corticosteroids aldosterone cortisol androgens  Pancreas Retroperitoneal, inferior and dorsal to stomach  Pancreatic Hormones 1-2 million islets produce hormones – 98% of organ produces digestive enzymes (exocrine) Insulin (from  cells) – secreted after meal with carbohydrates raises glucose blood levels – stimulates glucose and amino acid uptake – nutrient storage effect (stimulates glycogen, fat and protein synthesis) Is a growth factor (stimulates protein synthesis) – antagonizes glucagon  Pancreatic Hormones cont. Glucagon (from  cells) – secreted during fasting or in very low carbohydrate and high protein diets – stimulates glycogenolysis, fat catabolism (release of FFA’s) and promotes absorption of amino acids for gluconeogenesis Somatostatin (from delta () cells) – secreted with rise in blood glucose and amino acids after a meal – paracrine secretion = inhibits secretion of insulin and glucagon by  and  cells Remember somatostatin blocks release of GH and TSH – High CHO diet blocks release of GH – Somatostatin is also known as growth hormone-inhibiting hormone (GHIH) – Somatostatin is secreted by delta cells at several locations in the digestive system, namely the pyloric antrum, the duodenum and the pancreatic islets.  Glucose regulation Hyperglycemic hormones raise blood glucose – GH, epinephrine, NE, glucagon and glucocorticoids Hypoglycemic hormones lower blood glucose – insulin  Histology of Ovary Follicles = egg surrounded by granulosa cells  Ovary Granulosa cells in the wall of ovarian follicle – produces estradiol, first half of menstrual cycle Corpus luteum: forms from the follicle cells after ovulation – produces progesterone and estradiol for 12 days or 8-12 weeks with pregnancy Functions of estradiol and progesterone – development of female reproductive system and female physique including bone growth – regulate menstrual cycle, sustain pregnancy – prepare mammary glands for lactation Both follicle and corpus luteum secrete inhibin: suppresses FSH secretion  Testes interstitial cells of Leydig (between seminiferous tubules) – produce testosterone and some estrogen Functions – development of male reproductive system and male physique – sustains sperm production and sex drive Sustentacular or sertoli cells – secrete inhibin which suppresses FSH secretion which stabilizes sperm production rates Endocrine Functions of Other Organs  Endocrine Functions of Other Organs cont. Heart – – atrial natriuretic peptide released with an increase in BP –  blood volume and  BP by  Na+ and H2O loss by kidneys Skin - helps produce D3 Liver – 15% of erythropoietin (stimulates bone marrow) – angiotensinogen (a prohormone) precursor of angiotensin II – source of IGF-I (works with GH) – converts vitamin D3 to calcidiol – Hepcidin – promotes intestinal absorption of iron  Endocrine Functions of Other Organs Kidneys – produces 85% of erythropoietin – stimulates bone marrow to produce RBC’s – convert angiotensinogen to angiotensin I – converts calcidiol to calcitriol (active form of vitamin D)  absorption of Ca2+ by intestine and inhibits loss in the urine more Ca2+ available for bone deposition Stomach and small intestines (10 enteric hormones) – coordinate digestive motility and secretion Placenta – secretes estrogen, progesterone and others regulate pregnancy, stimulate development of fetus and mammary glands  Chemical classes of hormones Lipid derivatives Amino acid derivatives Peptide hormones Hormones derived from lipids Eicosanoid Synthesis Types of Hormones derived from lipids Hormone Synthesis: Steroid Hormones Synthesized from cholesterol – differs in functional groups attached to 4-ringed steroid backbone Lipid derived Hormones  Amino acid derivatives Monoamines – Catecholamines – Melatonin Thyroid hormones – T3 – T4 Hormones derived from peptides  Control of Hormone Release Humoral stimuli changing blood levels or some factor Neural stimuli sympathetic influence parasympathetic influence Hormonal stimuli positive feedback loops negative feedback loops Humoral stimuli: Control of parathyroid hormone levels Dropping blood levels calcium  Neural stimuli: Feedback loop with Oxytocin Neuroendocrine reflex – oxytocin release in response to nervous system signals suckling infant stimulates nerve endings activate hypothalamus posterior lobe oxytocin milk ejection more milk = more suckling more oxytocin more milk – oxytocin release in response to higher brain centers Baby’s cry stimulates hypothalamus and get milk ejection Hormonal stimuli: Negative Feedback Loop Control of thyroid hormone levels Negative feedback –  hormone levels at the target organ inhibits release of tropic hormones – Inhibits release of more hormone  Hormone Transport Monoamines and peptides are hydrophilic – mix easily with blood plasma Steroids and thyroid hormone are hydrophobic – must bind to transport proteins for transport – bound hormone - attached to transport protein, prolongs half-life to weeks protects from enzymes and kidney filtration – unbound hormone leaves capillary to reach target cell (half-life a few minutes) Transport proteins in blood plasma – albumin, thyretin and TBG (thyroxine binding globulin) bind to thyroid hormone – steroid hormones bind to globulins (transcortin) – aldosterone - no transport protein, 20 min. half-life  Hormone Receptors Located on plasma membrane, mitochondria, other organelles, or in nucleus Usually, thousands for a given hormone – hormone binding turns metabolic pathways on or off Exhibit specificity and saturation – Lock and key model  Hormone Mode of Action Hydrophobic hormones – Penetrate plasma membrane – enter nucleus – Bind to intracellular hormone receptors Hydrophilic hormones – must bind to cell- surface receptors  Intracellular Hormone Receptors Hydrophobic hormones Result in direct gene activation – Example thyroid hormones Hormone passes through plasma membrane Hormone binds to a receptor in the nucleolus Forms a hormone-receptor complex which translocates to the DNA Binds to hormone-response element which is attached to a gene promoter Gene activation Transcription Translation – Na+-K+ ATPase produced » generates heat  Thyroid Hormone Effects Other effects of TH Binds to receptors on – mitochondria  rate of aerobic respiration – ribosomes helps protein synthesis  Extracellular Hormone Receptors (Hydrophilic Hormones require a receptor on the surface of the cell) example: cAMP as Second Messenger 1) Hormone binding activates G protein (binds to GTP) 2) Activates adenylate cyclase 3) Produces cAMP 4) Activates kinases (PKA) 5) Activates enzymes 6) Metabolic reactions: – Change protein synthesis rates – Activate or inactivate enzymes – Trigger secretion – Change membrane potentials  Termination of signal Stop release of hormone Hormone signals must be turned off by – Enzymatic breakdown of hormone at target tissue – Take up and degraded by liver and kidney Excreted in bile or urine Deactivation of G-protein by hydrolysis of GTP Breakdown of cAMP by phosphodiesterases Removal of phosphate groups by phosphotases Hydrophilic Hormones: Mode of Action Other 2nd Messengers Hormones may use different second messengers in different tissues.  Modes of Hormone Action Advantage of the second messenger system – Amplification – Regulation – Cross-talk between systems Enzyme Amplification Modulation of Target Cell Sensitivity Up-regulation – Increase synthesis of receptors – Reduce rate of degradation of receptors  Target Cell Sensitivity Modulation Down-regulation – Reduce synthesis of receptors – Increase rate of degradation of receptors  Hormone Interactions Most cells sensitive to more than one hormone and exhibit interactive effects – Interactions between different hormones Permissive effects – additive Synergistic effects – exponential Antagonistic effects – Opposite effects  Endocrine Disorders Variations in hormone concentration and target cell sensitivity have noticeable effects on body Hyposecretion – inadequate hormone release – tumor or lesion destroys gland head trauma affects pituitary gland’s ability to secrete ADH – diabetes insipidus = chronic polyuria Hypersecretion – excessive hormone release – tumors or autoimmune disorder toxic goiter (graves disease) – antibodies mimic effect of TSH on the thyroid  Pituitary Disorders Hypersecretion of growth hormones – acromegaly – thickening of the bones and soft tissues – problems in childhood or adolescence gigantism if oversecretion dwarfism if hyposecretion  Thyroid Gland Disorders Congenital hypothyroidism ( TH) – infant suffers abnormal bone development, thickened facial features, low temperature, lethargy, brain damage Myxedema (adult hypothyroidism,  TH) – low metabolic rate, sluggishness, sleepiness, weight gain, constipation, dry skin and hair, cold sensitivity,  blood pressure and tissue swelling Endemic goiter (goiter = enlarged thyroid gland) – dietary iodine deficiency, no TH, no - feedback,  TSH Toxic goiter (Graves disease) – antibodies mimic TSH, TH, exophthalmos  Parathyroid Disorders Hypoparathyroid – surgical excision during thyroid surgery – fatal tetany 3-4 days Hyperparathyroid = excess PTH secretion – tumor in gland – causes soft, fragile and deformed bones –  blood Ca2+ – renal calculi  Adrenal Disorders Cushing syndrome - excess cortical secretion – hyperglycemia, hypertension, weakness, edema – muscle and bone loss occurs with protein catabolism – buffalo hump and moon face = fat deposition between shoulders or in face Adrenogenital syndrome (AGS) – adrenal androgen hypersecretion; accompanies Cushing – enlargement of external sexual organs in children and early onset of puberty – masculinizing effects on women (deeper voice and beard growth)  Diabetes Mellitus Signs and symptoms of hyposecretion of insulin – polyuria, polydipsia, polyphagia – hyperglycemia, glycosuria, ketonuria – osmotic diuresis blood glucose levels rise above transport maximum of kidney tubules, glucose remains in urine (ketones also present) increased osmolarity draws water into urine  Types of Diabetes Mellitus Type I (IDDM) - 10% of cases – some cases have autoimmune destruction of  cells, diagnosed about age 12 – treated with diet, exercise, monitoring of blood glucose and periodic injections of insulin Type II (NIDDM) - 90% – insulin resistance failure of target cells to respond to insulin – 3 major risk factors are heredity, age (40+) and obesity – treated with weight loss program of diet and exercise – oral medications improve insulin secretion or target cell sensitivity  Pathology of Diabetes Acute pathology: cells cannot absorb glucose, rely on fat and proteins (weight loss, weakness) – fat catabolism  FFA’s in blood and ketone bodies – ketonuria promotes osmotic diuresis, loss of Na+ and K+ – ketoacidosis occurs as ketones  blood pH if continued causes dyspnea and eventually diabetic coma Chronic pathology – chronic hyperglycemia leads to neuropathy and cardiovascular damage from atherosclerosis retina and kidneys (common in type I), atherosclerosis leads to heart failure (common in type II), and gangrene  Hyperinsulinism From excess insulin injection or pancreatic islet tumor Causes hypoglycemia, weakness and hunger – triggers secretion of epinephrine, GH and glucagon side effects: anxiety, sweating and  HR Insulin shock – uncorrected hyperinsulinism with disorientation, convulsions or unconsciousness