Chapter 17 Handout PDF

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Notes from Dr. Siddique's class. Chapter is from the textbook. Not sure which edition....

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Chapter 17

The Endocrine System For the body to function as ONE, its cells/organs must communicate with each other. The communication is necessary to maintain homeostasis. 2 systems do that: Nervous and Endocrine. We discuss the latter here.

17.1 Overview of the Endocrine System Cells connect or communicate with each other by the following 4 Principal ways: – Gap junctions • – Neurotransmitters • – Paracrines (local hormones) • secreted into tissue fluids to effect nearby cells – Hormones • chemical messengers that travel in the bloodstream Components of Endocrine System • Hormone – chemical messenger secreted into _______________, stimulates response in another tissue or organ • Target cells – have receptors for hormone • Endocrine glands – produce ______________ • Endocrine system – includes endocrine organs (thyroid, pineal, etc) – includes hormone producing cells in organs such as brain, heart and small intestine Endocrine Organs

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Major organs of endocrine system (see Fig)

A. Comparison of Endocrine and Exocrine Glands • Exocrine glands – _______ carry secretion to body surface or other organ cavity, extracellular effects • Endocrine glands – no ______, release hormones into tissue fluids, have dense capillary networks to distribute hormones, intracellular effects, alter target cell metabolism B. Comparison of the Nervous and Endocrine Systems (see Table) • Means of communication – nervous system has both electrical and chemical methods 1

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endocrine system has only chemical methods • Speed and persistence of response – nervous system reacts quickly (1-10 msec) and stops quickly – endocrine system reacts slowly (hormone release in seconds or days), effect may continue for weeks • Adaptation to long-term stimuli – nervous system adapts quickly and response declines – endocrine system has more persistent responses • Area of effect – nervous system effects are targeted and specific (one organ) – endocrine system may have general, widespread effects on many organs Similarities in Nervous and Endocrine Systems (NOT NEEDED for test) • Several chemicals function as both hormones and neurotransmitters – norepinephrine, cholecystokinin, thyrotropin-releasing hormone, dopamine and antidiuretic hormone • Some hormones secreted by neuroendocrine cells (neurons that secrete into ECF) – oxytocin and catecholamines • Both systems with overlapping effects on same target cells – norepinephrine and glucagon cause glycogen hydrolysis in liver • Systems regulate each other – neurons trigger hormone secretion – hormones stimulate or inhibit neurons

17.2 The Hypothalamus and Pituitary Gland A. Anatomy I. Hypothalamus • Shaped like a flattened funnel, forms floor and walls of _________ ventricle

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Regulates primitive functions from water balance to ______ drive Many functions carried out by pituitary gland

II. Pituitary Gland (Hypophysis) • Suspended from hypothalamus by a stalk called _________________. – Location and size: housed in _______________ of ________________ bone • Two sections: Adenohypophysis & Neurohypophysis. • Adenohypophysis: – Anterior 3/4 – Has 2 parts: large anterior lobe (“pars distalis”) and “pars tuberalis”. – Connected to hypothalamus by hypophyseal portal system • Neurohypophysis: – Posterior 1/4 – Has 3 parts: the posterior lobe “pars nervosa” is the largest part.

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– Nerve fibers are from neurons in hypothalamus that travel down the stalk as hypothalamo-hypophyseal tract. These carry hormones made by the neurons to the posterior lobe where the hormones are stored until released in response to a nerve signal. B. Hypothalamic Hormones – Produces 8 hormones: 6 controls Anterior pit. (4 releasing & 2 inhibitory: memorize Table) and 2 into Posterior pit. (OT and ADH). C. Anterior Pituitary hormones: Anterior lobe synthesizes and secretes 6 principal hormones: Gonadotropins target gonads: FSH (follicle stimulating hormone) and LH (luteinizing hormone) – TSH (thyroid stimulating hormone) – ACTH (adrenocorticotropic hormone) – PRL (prolactin) – GH (growth hormone)

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D. Posterior Pituitary Hormone Posterior lobe store and release ADH and OT. These are produced in Hypothalamus, then transported down to post. lobe by hypothalamo-hypophyseal tract. 3 “axis” (hormonal interrelationship between hypo, pit, & other remote organs - the way endocrine glands interact). See Fig: – hypothalamic-pituitary-gonadal axis – ,, ,, thyroid ,, – ,, ,, adrenal ,, Actions of the Pituitary Hormones Anterior Lobe Hormones • FSH – Ovaries, stimulates development of eggs and follicles – Testes, stimulates production of sperm • LH – Females, stimulates ovulation, stimulates corpus luteum to secrete progesterone and estrogen – Males, stimulates interstitial cells of testes to secrete testosterone

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TSH – Stimulates growth of thyroid gland and secretion of TH (thyroid hormone) • ACTH or corticotropin – Regulates response to stress, stimulates adrenal cortex to secrete corticosteroids (especially cortisol) that regulate glucose, fat & protein metabolism

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PRL – Female, milk synthesis after delivery – Male,  LH sensitivity, thus  testosterone secretion • GH or Somatotropin – promotes tissue growth: directly affects mitosis and cellular differentiation of many organs (cartilage, bone, muscle, fat etc) and not a particular organ - controlled by GHIH (GH inhibiting hormone) and GHRH (GH ______________). – indirectly stimulates liver to produce insulin-like growth factors (IGF) – these in turn target cells in diverse tissues, has longer half-life.

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Functions of GH-IGF : Proteins & electrolytes essential for tissue growth. So, GH protein synthesis,  protein catabolism  FFA (free fatty A.) and glycerol release to decrease protein use CHO metabolism: glucose sparing effect = less glucose used for energy Electrolyte balance

Posterior Lobe Hormones

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ADH (also called vasopressin) – Targets kidneys to  water retention  reduce urine volume  prevent dehydration • Oxytocin – Labor contractions, lactation E. Control of Pituitary Secretion Hypothalamic and Cerebral Control

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Anterior lobe control - releasing hormones & inhibiting hormones of hypothalamus

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Posterior lobe control - neuroendocrine reflexes – hormone release in response to nervous system signals • suckling infant stimulates nerve endings  hypothalamus  posterior lobe  oxytocin  milk ejection (not needed for exam) – hormone release in response to higher brain centers • milk ejection reflex can be triggered by a baby's cry (not needed for exam) Control of Pituitary: negative feedback (see Fig) –  target organ hormone levels inhibits release of tropic hormones

17.3 Other Endocrine Glands A. The Pineal Gland • Produces serotonin by day, converts it to melatonin at night B. The Thymus 4

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Location: mediastinum, superior to heart, Involution after puberty Secretes hormones that regulate development and later activation of Tlymphocytes C. The Thyroid Gland • Largest endocrine gland with high rate of blood flow • Anterior and lateral sides of trachea; 2 large lobes connected by isthmus – Gland is made of sacs called thyroid follicles (lined by follicular cells) that are filled with colloid. – Follicular cells secrete 2 hormones, T3 (triiodothyronine) and T4 (thyroxine). The THs are synthesized from iodine & tyrosine (an AA) – Thyroid hormones •  body’s metabolic rate and O2 consumption •  heat production •  heart rate and contraction strength •  respiratory rate •  appetite – Parafollicular cells (C cells) produce calcitonin that  blood Ca+2, promotes Ca+2 deposition and bone formation D. The Parathyroid Glands • Partially embedded in the posterior surface of thyroid, usually 4

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PTH release is in response to hypocalcemia  blood Ca+2 levels by promoting synthesis of calcitriol that in turn  absorption of Ca+2,  urinary excretion of Ca+2,  bone resorption (meaning?)

E. The Adrenal Gland (Suprarenal gland) Has inner medulla & outer cortex The Adrenal Medulla • Sympathetic ganglion - consists of modified neurons called chromaffin cells Stimulation causes release of catecholamines (norepinephrine & epinephrine) that: – increases BP and heart rate – increases blood flow to skeletal muscle – increases pulmonary air flow – decreases digestion and urine formation – stimulates gluconeogenesis and glycogenolysis   bl glucose – inhibit insulin secretion  saves glucose  ensure adequate supply to N.S. The Adrenal Cortex • Layers: (outer) zona glomerulosa, (middle) zona fasciculata, (inner) zona reticularis

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Synthesizes steroid hormones known as Corticosteroids Mineralocorticoids (zona glomerulosa) • principal hormone is aldosterone that controls electrolyte balance (promotes Na+ & water retention and K + excretion – controlled by Renin-Angiotensin pathway and blood levels of K +) – Glucocorticoids (zona fasciculata) • especially cortisol (hydrocortisone), stimulates fat & protein catabolism, gluconeogenesis (from a.a.’s + FA’s) and release of fatty acids and glucose into blood • anti-inflammatory effect – Sex steroids/gonadocorticoids (zona reticularis) • androgen (including DHEA which other tissues convert to testosterone) and estrogen (important after menopause) F. The Pancreatic Islets The Pancreas is an elongated, spongy gland, inferior & dorsal to stomach. Mostly Retro? 1-2 Million pancreatic islets (2%) called islets of langerhans produce hormones (________), the rest (98% of the organ) produces digestive enzymes (___________). 3 main types of endocrine cells: , , and  (skip the other 2) • Glucagon (from  or A cells) – secreted in very low carbohydrate and high protein diet or fasting – stimulates glycogenolysis, fat catabolism (release of FFA’s) and promotes absorption of amino acids for gluconeogenesis Overall affect of glucagon is to _____________ blood glucose level. • Insulin (from  or B cells) – secreted after meal with carbohydrates that raises blood glucose levels – stimulates glucose and amino acid uptake by cells for later use – nutrient storage effect (stimulates glycogen, fat, and protein synthesis) – antagonizes glucagon Overall effect of insulin is to _______________ blood glucose level. • Somatostatin (from delta/ or D cells) – secreted with rise in blood glucose and amino acids after a meal – paracrine secretion = modulates secretion of  +  cells Hyperglycemic hormones raise blood glucose – glucagon, epinephrine, norepinephrine, cortisol & corticosterone Hypoglycemic hormones lower blood glucose - ___________?? G. The Gonads Ovary

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Granulosa cells in wall of ovarian follicle Produces estradiol (a form of estrogen), first half of menstrual cycle Corpus luteum: follicle after ovulation 6

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Produces estradiol and progesterone for 12 days or 8-12 weeks with pregnancy

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Functions of estradiol and progesterone development of female reproductive system and physique including bone growth regulate menstrual cycle, sustain pregnancy prepare mammary glands for lactation

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Interstitial cells (between seminiferous tubules) produce testosterone and estrogen • Functions – development of male reproductive system and physique – sustains sperm production and sex drive • Sustentacular or sertoli cells secrete inhibin  suppresses FSH secretion which stabilizes sperm production rates H. Endocrine Functions of Other Tissues and Organs Skin – keratinocytes help produce D3, first step in synthesis of calcitriol Liver – converts vitamin D3 to calcidiol – secretes about 15% of erythropoietin  stimulates _____ formation – secretes angiotensinogen – a precursor of angiotensin II, a vasoconstrictor Kidneys – converts calcidiol to calcitriol (active form of vitamin D) – produces 85% of erythropoietin – stimulates bone marrow to produce _______ – convert angiotensinogen to angiotensin I Heart – atrial natriuretic peptide (ANP) released with an  BP   bl volume   BP Stomach and small intestines (10 enteric hormones) – coordinate digestive motility and secretion Placenta - secretes estrogen, progesterone and others Skip the other 2 See Table for a summary of hormones

17.4 Hormones and Their Actions A. Hormone Chemistry 3 chemical classes: Steroids (derived from cholesterol); Peptides & Monoamines (derived from amino acids): - Skip B. Hormone Synthesis and C. Hormone Transport - Skip D. Hormone Receptors and Mode of Action – Skip E. Enzyme Amplification  One hormone molecule does not trigger the synthesis or activation of just one enzyme molecule. It activates thousands of enzyme molecules thru a cascade effect called enzyme amplification. This enables a very small stimulus to produce a very large effect. So, hormones are needed in very small quantities.

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F. Modulation of Target-Cell Sensitivity  Target cells can modulate or adjust their sensitivity to a hormone, and one hormone can alter a target cell’s sensitivity to another.  Up-regulation – a cell increases the # of hormone receptors & becomes more sensitive to the hormone.  Down-regulation – a cell reduces its # of receptors & become less sensitive to the hormone. G. Hormone Interactions • Most cells sensitive to more than one hormone and exhibit interactive effects

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Synergistic effects: 2 or more hormones act together – sum effect higher Permissive effects: one hormone enhances response to a second hormone Antagonistic effects: one opposes the action of another

H. Hormone Clearance – Skip

17.5 Stress and Adaptation

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Any situation that upsets homeostasis and threatens one’s physical or emotional well-being is defined as stress  Physical causes (stressors): injury, surgery, infection, intense exercise, temperature extremes, pain, malnutrition etc  Emotional causes: anger, grief, depression, guilt, anxiety etc Details - Skip

17.6 Eicosanoids and Paracrine Signaling Paracrine Secretions • Chemical messengers that diffuse short distances and stimulate nearby cells – Examples: histamine from mast cells in connective tissue causes relaxation of blood vessel smooth muscle, catecholamines diffuse from adrenal medulla to cortex etc. • Eicosanoids are paracrines w/ 20-C backbones. - Leukotrienes - mediate allergic and inflammatory reactions – Prostacyclin: produced by blood vessel walls, inhibits blood clotting and vasoconstriction – Thromboxanes: produced by blood platelets after injury, they override prostacyclin and stimulate vasoconstriction and clotting – Prostaglandins: diverse group including » PGE’s: relaxes smooth muscle in bladder, intestines, bronchioles, uterus and stimulates contraction of blood vessels » PGF’s: opposite effects

17.7 Endocrine Disorders (Skip, except for Diabetes at the end)

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Variations in hormone concentration and target cell sensitivity have noticeable effects on the body

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Hyposecretion – can be caused by tumor or lesion  destroys gland  inadequate hormone release. Example: Head trauma  affects pituitary  secretion of ADH  diabetes insipidus = chronic polyuria • Hypersecretion – tumors or autoimmune disorder  excessive hormone release

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Pituitary hypersecretion of growth hormone  acromegaly (in adults), gigantism (in childhood or adolescence). Dwarfism (in childhood) if hyposecretion. • Myxedema (adult hypothyroidism,  TH) – low metabolic rate, sluggishness, sleepiness, weight gain, cold sensitivity,  blood pressure and tissue swelling

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Endemic goiter (goiter = enlarged thyroid gland) dietary iodine deficiency, no TH, no negative feedback Toxic goiter (Graves disease) antibodies mimic TSH, TH Hypoparathyroid Accidental surgical excision during thyroid surgery - fatal tetany Hyperparathyroid = excess PTH secretion due to tumor in gland Cushing syndrome is excess cortical secretion  buffalo hump & moon face causes hyperglycemia, hypertension, weakness, edema

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Adrenogenital syndrome (AGS): causes enlargement of external sexual organs in children & early onset of puberty 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, osmolarity  and draws water into urine – kidney tubules can not reabsorb glucose fast enough if no insulin is present – osmotic diuresis results due to excess glucose and ketones in tubules 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 or insulin pump • 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

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Pathology of Diabetes - not needed Hyperinsulinism (Skip) • From excess insulin injection or pancreatic islet tumor – Causes hypoglycemia, weakness and hunger, sweating and  HR

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Insulin shock uncorrected hyperinsulinism with disorientation, convulsions or unconsciousness.

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