Chapter 9 The Endocrine System

1. Chapter 9 The Endocrine System Biology 112 Tri-County Technical College Pendleton, SC

2. Hormones are flowing… • Hormones are chemical substances secreted into extracellular fluid that regulate activity of other cells • Hormones circulate to all organs but affect ONLY certain tissue cells/organs referred to as its TARGET CELLS/ORGANS • Target MUST have specific protein receptors on its plasma membrane or interior to which hormone can attach

3. Hormones, cont. • Reproduction, growth & development, body’s defenses against stressors, electrolyte, water, & nutrient balance of blood, regulating metabolism & energy balance • Typically one or more of following occur as result of hormone action: • changes in PM permeability/electrical state • synthesis of proteins or regulatory molecules • activation/inactivation of enzymes • stimulation of mitosis/meiosis

4. Getting there • Steroid hormones able to diffuse across PM • Nonsteroid hormones require membrane receptors and utilize signal-transduction mechanism (second messengers) • One of three mechanisms responsible for stimulating endocrine gland • HORMONAL • HUMORAL • NEURAL

5. Hormonal Action, Visual

6. Stimulation, Visual

7. Been there…done that • Hormonal secretion triggered by some internal/external stimulus • Rising hormone levels inhibit further hormone release even while promoting responses in target organs • WOW!!! Negative feedback model again • **End product controls the rate of the reaction or event

8. Endocrine Glands • Endocrine glands (ductless) release their secretions into blood or lymph • Endocrine glands have a very rich blood supply • Hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal, thymus, pancreas, and gonads (testes/ovaries)

9. Location, Visual

10. Pituitary Gland • Pituitary gland about the size of a grape and hangs by a stalk from inferior surface of hypothalamus of the brain • surrounded by “turk’s saddle” of sphenoid bone • Has two functional lobes • Anterior pituitary arises from glandular tissue • Posterior pituitary arises from nervous tissue • Anterior hormones: growth hormone (GH), prolactin (PRL), follicle-stimulating (FSH), luteinizing (LH), Thyroid stimulating (TSH) and Adrenocorticotropic (ACTH)

11. Pituitary, cont. • Growth hormone and prolactin exert their major effects on nonendocrine targets • FSH, LH, TSH, and ACTH are all TROPHIC hormones • Trophic hormone is hormone that regulates the activity of another ENDOCRINE gland • All anterior pituitary hormones are proteins/peptides; act through 2nd messengers; are regulated by hormonal stimuli, and operate via negative feedback mechanism (in most cases)

12. Anterior Pituitary, Visual

13. Growth Hormone • GH is protein-sparing & anabolic hormone causing amino acids to build into proteins • Stimulates MOST target cells to grow in size and divide • Causes fats to be broken down for energy • Spares body’s supply of glucose thereby helping to maintain blood sugar homeostasis

14. Pituitary Abnormalities • Hyposecretion of GH during childhood leads to pituitary dwarfism • body proportions fairly normal but person is living miniature (adult height ~ 4 feet) • Hypersecretion during childhood leads to gigantism • individual becomes extremely tall (8-9 feet) • If hypersecretion occurs after long bone growth ended = acromegaly • lower jaw and bony ridges under eyebrow enlarge as does hands and feet; thickening of soft tissue leads to coarse/malformed facial features • Most hypersecretion of endocrine glands caused by tumors of affected gland

15. Prolactin • Abbreviated as PRL • Protein hormone whose only known target in humans is the breast • After childbirth, it stimulates and maintains milk production by mother’s breasts • Its function is males is NOT known

16. Same song, different verse… • Adrenocorticotrophic hormone = ACTH • Regulates activity of the cortex portion of the adrenal gland • Thyroid-stimulating hormone = TSH • TSH also known as thyrotropic hormone (TH) • Influences growth and activity of the thyroid gland

17. Follicle Stimulating Hormone • Abbreviated as FSH • Regulates activity of gonads (ovaries/testes) • In females, FSH stimulates follicle development in ovaries • As follicles mature, they produce estrogen and eggs are readied for ovulation • In males, FSH stimulates sperm development by the testes

18. Luteinizing Hormone • Abbreviated LH • In females, LH triggers ovulation of egg from ovary • Also causes ruptured follicle to become corpus luteum • LH then stimulates corpus luteum to produce progesterone and some estrogen • In men, LH is referred to as interstitial cell-stimulating hormone (ICSH) • stimulates testosterone production by interstitial cells

19. Pituitary and Sterility • Hyposecretion of FSH or LH leads to sterility in both males and females • Hypersecretion does NOT appear to cause any problem(s) • Some drugs used to produce fertility stimulate release of FSH and LH • Multiple births fairly common after their administration

20. Anterior Pituitary/Hypothalamus • Pituitary used to be called “master gland” • Release of pituitary’s hormones controlled by releasing and inhibiting hormones produced by hypothalamus • Hypothalamus releases these regulatory hormones into portal circulation which connects blood supply of hypothalamus with that of anterior pituitary

21. Posterior Pituitary • Posterior pituitary (neural tissue) STORES two hormones produced by hypothalamus • Oxytocin and antidiuretic hormone (ADH) • Both are peptide hormones • Produced in hypothalamus • Transported along axons of hypothalamic neurosecretory cells to posterior pituitary for storage • Released into blood in response to nerve impulses from the hypothalamus

22. Posterior Pituitary, Visual

23. OH!!! for Oxytocin • Released in significant amounts only during childbirth and in nursing women • Stimulates powerful contractions of the uterine muscles during labor, sexual relations, and when female is nursing • Also causes milk ejection (letdown reflex) in nursing women • Natural/synthetic oxytocic drugs (pitocin) used to induce/hasten labor, stop postpartum bleeding, and stimulate milk ejection reflex

24. Antidiuretic Hormone • Diuresis is urine production • Antidiuretic is chemical that inhibits and/or prevents urine production • ADH causes kidneys to reabsorb more water from forming urine • Results in urine volume DECREASE and blood volume INCREASE • In large amounts, ADH increases blood pressure by causing constriction of arterioles (small arteries) • ADH sometimes called VASOPRESSIN

25. Diabetes Insipidus • Hyposecretion of ADH leads to condition of excessive urine output called diabetes insipidus • Individuals with this problem are continually thirsty and drink large amounts of water

26. Thyroid Gland • Thyroid located at base of throat, inferior to Adam’s apple where easily palpated • Large gland of two lobes joined by central mass called isthmus • Internally, composed of hollow structures called follicles which store sticky colloidal material • Thyroid iodine-containing hormone derived from colloid • Produces 2 active hormones: T3 and T4 • Also produces calcitonin (thyrocalcitonin)

27. Thyroid, Visual

28. T3 and T4 • Thyroid hormone (body’s major metabolic hormone) actually two iodine-containing hormones • Tetraiodothyronine (thyroxine or T4) • Triiodothyronine (T3) • Thyroxine (T4) is major hormone secreted by thyroid follicles • Most T3 formed at target tissues by conversion of T4 to T3

29. The T’s, cont. • Both are very similar—two tyrosine amino acids linked by either 3 or 4 iodine atoms • Controls rate at which glucose is converted to chemical energy and heat • EVERY cell in body is target for thyroid hormone • Also important for normal tissue growth and development especially in reproductive and nervous systems

30. Remember it well… • GOITER is enlargement of thyroid gland • caused by diet deficient in iodine • TSH keeps calling for thyroxine and thyroid gland continues to enlarge to make more… • Only peptide part of molecule is made but without iodine it is NONFUNCTIONAL • fails to provide negative feedback to inhibit TSH release • Uncommon in US today because of iodized salt

31. Cretinism, Myxedema, and more • Cretinism results in dwarfism where adult body proportions remain childlike • Caused by hyposecretion of throxine in early childhood • Untreated leads to mental retardation, scanty hair, and very dry skin • Discovered early, HR can prevent signs and symptoms of deficiency

32. C, M, and more…cont. • Myxedema caused by hyposecretion of thryoxine during adulthood • Mental and physical sluggishness, puffiness of face, fatigue, poor muscle tone, low body temperature, obesity, and dry skin • Oral thyroxine is prescribed • HYPERTHYROIDISM usually results from tumor of thyroid gland = extreme overproduction of thyroxine

33. C, M, and more…cont. • High metabolic rate, intolerance of heat, rapid heart beat, weight loss, nervous and agitated behavior, & inability to relax • Grave’s disease is one form of hyperthyroidism • May also cause thyroid to enlarge & eyes to bulge or protrude anteriorly in condition called exophthalmos

34. Calcitonin • Calcitonin (thyrocalcitonin) is second major hormone of the thyroid gland • Decreases blood calcium levels by causing calcium to be deposited in bone • Antagonistic to parathyroid hormone • Made by “C cells” found in connective tissue between follicles • Released into blood in response to >ing levels of blood calcium • Believed calcitonin production is meager or absent in elderly • Calcitonin is hypocalcemic hormone; < calcium in blood

35. Calcium Homeostasis, Visual

36. Parathyroid Glands • Are tiny masses of glandular tissue found on posterior surface of thyroid gland • Typically 2 on each lobe (8 reported) • Secrete parathyroid hormone (PTH) or parathormone • **Most important regulator of calcium ion (Ca2+) in blood • Calcium levels drop below certain level, parathyroids release PTH which stimulates bone destruction cells (osteoclasts)

37. Parathyroids, cont. • Osteoclasts break down bone matrix and increase blood levels of calcium • **PTH is hypercalcemic hormone because it acts to > blood levels of calcium • Another example of negative feedback • PTH also stimulates kidneys and intestine to absorb MORE calcium from forming urine and foodstuff

38. Hypo versus Hypercalcemia • Hypocalcemia can be caused by hypoparathyroidism (poor diet, lack of vitamin D, and/or renal failure) • Blood calcium levels drop too low, neurons become extremely irritable/overactive • Neurons deliver impulses to muscles at such rapid rate that muscles go into uncontrollable spasms (tetany) • Convulsions, intestinal cramps, weak heartbeat, cardiac arrhythmias, osteoporosis (what a lesson)

39. Hypo/Hyper, cont. • Hypercalcemia results when calcium blood levels become too high • Can be caused by hyperparathyroidism (cancer, vitamin D toxicity, calcium supplement overdose) • Confusion, muscle pain, cardiac arrhythmias, kidney stones, fatigue, and calcification of soft tissue • Is it catching…????

40. Adrenal Glands • Adrenal glands curve over top of kidneys • Each is structurally/functionally two endocrine glands • Like pituitary, the adrenal has glandular (cortex) and neural (medulla) parts • Central medulla enclosed by adrenal cortex which contains three separate layers of cells • Adrenal cortex produces 3 major groups of STEROID hormones called corticosteroids

41. Adrenal Glands, cont. • Mineralocorticoids, Glucocorticoids, and sex hormones • Mineralocorticoids, mainly aldosterone, produced by outermost adrenal cortex layer • Important in regulating mineral (salt) content of blood—especially [ ] of sodium and potassium ions • Their target is kidney tubules that selectively reabsorb minerals or allow them to be flushed out in urine

42. Adrenal glands, cont. • Blood levels of aldosterone >, kidney tubule cells reclaim >ing amounts of sodium ions • Allows more potassium ions to be excreted in urine • When sodium reabsorbed, water follows • Results in >ed blood volume and blood pressure • Mineralocorticoids help regulate both water and electrolyte balance in body fluids

43. Aldosterone Release, Visual

44. Adrenals and Glucocorticoids • Cortisone & Cortisol are 2 glucocorticoids produced by MIDDLE cortex layer • Promote normal cell matabolism and help body resist long-term stressors primarily by >ing blood glucose levels • High levels of glucocorticoids in blood prompt body cells to convert fats and proteins to glucose • Glucocorticoids are hyperglycemic hormones

45. Glucocorticoids cont. • Help control inflammation by <ing edema • Reduce pain by inhibiting pain-causing molecules called prostaglandins • Often prescribed for patients with rheumatoid arthritis to suppress inflammation • **Glucocorticoids released from adrenal cortex in response to rising blood levels of ACTH

46. Adrenals and Sex hormones • Regardless of gender, adrenal cortex produces small amounts of both male and female sex hormones throughout life • Innermost layer of adrenal cortex produces the bulk of the adrenal-produced sex hormones • Androgens (male hormones) and some estrogen also produced

47. Addison’s Disease • Addison’s disease caused by hyposecretion of adrenal cortex hormones • Major sign is peculiar bronze skin tone • Aldosterone levels <; sodium & water lost from body = problems with electrolytes and water balance • causes muscles to become weak/shock possible • Low levels of glucocorticoids results in hypoglycemia = lessened ability to cope with stress (burnout) and suppression of immune system & increased susceptibility to infection • Complete lack of glucocorticoids=auf wiedersehen

48. Cushing’s Syndrome • Hypersecretion usually result of tumor • If tumor in middle cortex region, Cushing’s syndrome occurs • Excessive output of glucocorticoids results in “moon face” and appearance of “buffalo hump” of fat on upper back • Also high BP, hyperglycemia, and possible diabetes, weakening of bones, and severe depression of the immune system

49. Trying things on… • Tumor in zona reticularis of cortex layer can cause excessive production of either androgens or estrogen • If androgen >s dramatically, produces symptoms of adrenogenital syndrome • In women=gradual development of male secondary sexual characteristics (body and facial hair, adipose tissue distribution, and muscular development) • In estrogen >s, leads to gynecomastia • Male develops female secondary sexual characteristics

50. ANS and Adrenal Medulla • Adrenal medulla (like posterior pituitary) develops from neural tissue • When stimulated sympathetic NS neurons, its cells release 2 similar hormones • Hormones called catecholamines • Epinephrine (adrenaline) & norepinephrine (noradrenaline) • Sympathetic division called “fight or flight response” division of ANS • > heart rate, blood pressure, blood glucose levels and dilation of small passageways of lungs • Body better able to deal with short-term stressor • Causes the “alarm” stage of the stress response