The Endocrine System

1. The Endocrine System Anatomy & Physiology Chapter 10

2. Endocrine System • A regulating system of the rest of the body • Components • Endocrine glands • Do not have ducts, secretions go directly into bloodstream • Secrete hormones: operate distantly from their site of origin • Target organs (or target tissues) • Parts of the body that the hormones act upon

3. Hormone Chemistry • Classifications • Amines • Simple hormones, variation of AA tyrosine • Thyroxine, epinephrine, norepinephrine • Proteins • Long or short chains (peptides) of AA’s • Insulin, GH, calcitonin, ADH, ocytocin • Steroids • Made from cholesterol precursor • Estrogen, progesterone, testosterone

4. Regulation of Hormone Secretion • Negative Feedback Mechanisms • Effects of the hormone is “fed back” to the gland and the hormone secretion is then decreased • Thyroxine, insulin • Releasing hormones (releasing factors) • A chemical produced by the hypothalamus that causes the anterior pituitary gland to secrete its hormones • Growth hormone-releasing hormone (GHRH)

5. Regulation of Hormone Secretion • Antagonistic Pairs • Pairs of hormones that have opposite functions regulating some aspect of blood chemistry

6. The Pituitary Gland • Also called hypophysis • Has two parts • Anterior part • adenohypophysis • Posterior part • neurohypophysis

7. Posterior Pituitary Gland • Stores and secretes two hormones that are made by the hypothalamus • These hormones are secreted in response to hypothalamic nerve impulses • Two hormones • Antidiuretic hormone (ADH) • oxytocin

8. Posterior Pituitary Hormones • Antidiuretic hormone (ADH) • Also called vasopressin, a peptide hormone • Increases renal reabsorption of water • So decreases amount of urine output • Decreases sweating • Arteriolar vasoconstriction to maintain BP • Stimulus for ADH secretion • Decreased water content of the body • Senses by hypothalamic osmoreeptors

9. Posterior Pituitary Hormones • Oxytocin • A peptide hormone (9 AA’s) • Also secreted by placenta at end of gestation • Stimulates uterine contractions at end of pregnancy (myometrial smooth muscle) • Stimulates milk release from mammary glands • Hypothalamus stimulation via: • Stretching of cervix during labor • Infant sucking nipples

10. Anterior Pituitary Hormones • Growth Hormone (GH) • Thyroid-Stimulating Hormone (TSH) • Adrenocorticotropic Hormone (ACTH) • Prolactin • Follicle-stimulating Hormone (FSH) • Luteinizing Hormone (LH)

11. Growth Hormone (GH) • Also called somatotropin • GH regulation via 2 releasing hormones from hypothalamus • GHRH • Made during exercise & hypoglycemia • Somatostatin • GH inhibiting hormone (GHIH) • Made during hyperglycemia

12. GH • Made in growing children and in adults • Promotes growth via: • Makes insulin-like growth factor molecules • Increases AA transport into cells for protein synthesis or storage as CHO • Stimulates mitosis in tissues • Stimulates fat release from adipose (for energy production)

13. Disorders of GH • Pituitary dwarfism • GH deficiency in children, final height of 3-4 feet (Hyposecretion of GH) • Giantism • Hypersecretion of GH in children, excessive long bone growth, height up to 8 feet • Acromegaly • GH hypersecretion in adults, growth of bones other than long bones (face, jaw, hands, feet)

14. Thyroid-stimulating Hormone (TSH) • Also called thyrotropin • Secretion stimulated by TRH from hypothalamus • TRH made when metabolic rate decreases • Actions: • Increases thyroid gland growth • Increases secretion of T3 and T4 (thyroid hormones)

15. Adrenocorticotropic Hormone (ACTH) • Secretions is stimulated by CRH from the hypothalamus • Physical stress stimulates CRH production • Injury, infection, hunger, disease, exercise • Actions: • Increases adrenal cortex to secret its hormones • Cortisol and others

16. Prolactin • Complex secretion regulation • Hypothalamus: PRH and PIH • Breast-feeding stimulates prolactin release • Estrogen & progesterone effects on mammary tissue • Actions: • Initiates and maintains milk production

17. Follicle-stimulating Hormone(FSH) • Regulation via • GnRH (gonadotropin-releasing hormone) from hypothalamus • Inhibin (made by ovaries or testes) • Actions: • Stimulates growth of ovarian follicles • Stimulates estrogen secretion by follicles • Stimulates sperm production in testes

18. Luteinizing Hormone (LH) • Regulation via GnRH from hypothalamus • Actions: • Causes ovulation • Stimulates follicle to become corpus luteum • CL makes progesterone • Stimulates testes to secrete testosterone

19. Thyroid Gland • Located in the anterior neck • Largest of the endocrine organs • Two lobes connected by narrow isthmus • Thyroid follicles produce the hormones • Thyroxine (T4) • Triiodothyronine (T3) • Parafollicular cells make the hormone • calcitonin

20. Thyroid Hormones • T3 and T4 actions: • Regulate energy production • Increases cell respiration of foods • Increases energy & heat production • Regulate protein synthesis • Increases rate of protein synthesis • Most important hormonal regulators of metabolic rate, necessary for normal physical & mental development

21. Regulation of Thyroid Hormone Secretion • Metabolic rate decreases • Hypothalamus senses this and secretes TRH • TRH stimulates anterior pituitary to release TSH • TSH stimulates thyroid to secrete T3 & T4, which increase metabolic rate • Metabolic rate increase shuts off this negative feedback mechanism

22. Thyroid Hormones • Calcitonin • Actions • Decreases reabsorption of Ca and P from bones to blood • Lowers blood levels of Ca and P • Maintains normal levels in bone matrix & blood • Most important during childhood • Regulation • Stimulus for secretion is hypercalcemia

23. Thyroid Disorders • Goiter • Enlargement of gland due to I deficiency • Cretinism • Hyposecretion of thyroid hormones during infancy, severe physical & mental retardation

24. Thyroid Disorders • Myxedema • Hyposecretion of thyroid hormone in adults • Low metabolic rate: lethargy, edema of face, low HR, weight gain, cold intolerance • Grave’s Disease • Autoimmune type of hyperthyroidism • High metabolic rate • Exophthalmos (eye protrusion)

25. Parathyroid Glands • Four glands, on posterior part of the thyroid lobes • Make parathyroid hormone (PTH) • Increases reabsorption of Ca & P from bones to blood, raises blood levels of these • Increases Ca & P absorption in intestines • Increases Ca reabsorption & P excretion in kidney • Overall effect: increases blood level of Ca and lowers blood level of P

26. PTH • Stimulus for PTH secretion: • hypocalcemia • Antagonistic hormone pair: • PTH and calcitonin • PTH hypersecretion: • Excessiva Ca loss from bones • Weakens bones • May be caused by parathyroid tumor

27. Pancreas • Upper abdominal organ • Exocrine & endocrine gland • Islets of Langerhans • Hormone-producing cells in pancreas • Two types • Alpha cells (make glucagon) • Beta cells (make insulin) • Delta cells (make somatostatin)

28. Glucagon • Actions: • Stimulates hepatic glycogenolysis • Breakdown of glycogen into glucose • Increases use of fats and AA’s for energy production (gluconeogenesis) • Secretion stimulated by: • Hypoglycemia • Between meals, during exercise, during other physically stressful times

29. Insulin • Actions: • Increases glucose transport into cells • Increases glycogenesis in liver and skeletal muscles (glycogen production) • Helps fatty acids (FA’s) & AA’s to be made into lipids and proteins • Overall effects: lowering of blood glucose and lipids • Stimulus for secretion: Hyperglycemia

30. Somatostatin • Made by delta cells • Identical to GHIH of hypothalamus • Actions: • Acts locally • Inhibits insulin & glucagon secretion • Slows absorption in small intestine

31. Diabetes Mellitus (DM) • A disease of glucose and carbohydrate metabolism characterized by • Chronic hyperglycemia • Insulin abnormalities of some sort • Type 1: • no insulin is made • Type 2: • insulin is made, but is not effective

32. Diabetes Mellitus: Types • Type 1 • Insulin-dependent DM (IDDM) • Childhood onset, often abrupt onset • Beta cells are destroyed • Possible autoimmune response to virus • Some genetic predisposition • No insulin can be made without beta cells • Treatment: • Insulin administration

33. Diabetes Mellitus: Types • Type 2: • Non-insulin-dependent (NIDDM) • Gradual onset during mature years • Insulin receptors on cell membranes are lost • Insulin is made, but is not as effective • Risk factors: Family history, obesity • Treatment: exercise, diet, oral meds or insulin or combination

34. Diabetes Mellitus • Three major symptoms: • Polyuria, polydipsia, polyphagia • Emergency condition: Ketoacidosis • Excess glucose converted to ketones, organic FA’s, in liver and these acculumate • Long-term effects: • Thickens walls of microvasculature so oxygen and nutrient exchange slows • Affects kidneys, retina, distal extremities, heart

35. Adrenal Glands • Suprarenal glands • Paired glands • One on superior aspect of each kidney • Parts of each adrenal gland: • Cortex (outer part) • Mineralocorticoid, glucocorticoids, sex hormones • Medulla (inner part) • Makes epinephrine & norepinephrine

36. Adrenal Medullary Hormones • Makes catecholamines • Sympathomimetic hormones • Secretion stimulated by sympathetic impulses from hypothalamus • Duplicate & prolong effects of sympathetic nervous system • Two hormones made: • Epinephrine & norepinephrine

37. Catecholamines • Norepinephrine: actions • Secreted in small amounts • Vasoconstriction of skin, viscera, skeletal muscle beds • Raises blood pressure

38. Catecholamines • Epinephrine • Secreted in larger amounts, more effective than sympathetic NS stimulation • Actions: • Increase HR, strength of cardiac contractions • Vasoconstriction of skin, viscera • Vasodilation in skeletal muscle • Bronchiolar dilation • Decreases peristalsis • Stimulates glycogenolysis in liver, increases use of fats, increases rate of cell respiration

39. Adrenal Cortical Hormones • All are types of steroid hormones • Types: • Mineralocorticoids • aldosterone • Glucocorticoids • cortisol • Sex Hormones • Estrogens and androgens in small amounts

40. Aldosterone • Most abundant mineralocorticoid • Target organ: kidney • Actions: Maintains blood volume & pressure • Increases Na reabsorption in kidney • H+ excreted in exchange by kidney tubules • HCO3- and Cl- follow Na back into blood • Water follows by osmosis • Increases K excretion in kidney tubules

41. Aldosterone • Stimulation of aldosterone secretion: • Via Na deficiency • Via loss of blood or dehydration (any low blood volume state) • Via renin-angiotensin mechanism • Stimulated by low blood volume sensed by kidneys • Culminates in formation of angiotensin II • Causes vasoconstriction & aldosterone secretion

42. Cortisol • A glucocorticoid released at times of stress • Stress produces CRH, stimulates ACTH release • Actions • Increases use of excess AA’s & fats for energy (gluconeogenesis) • Conserves glucose for use by brain (glucose sparing effect) • Anti-inflammatory • Blocks histamine effcts & stabilizes lysosome membranes, limiting tissue destruction • Is a brake on the positive feedback mechansim of inflammation

43. Adrenal Cortical Disorders • Addison’s Disease • Hyposecretion of adrenal cortical hormones • Hypoglycemia, hypovolemia, hyponatremia, hyperkalemia, weakness • Cushing’s Disease • Hypersecretion of cortical hormones • Truncal obesity, skin fragility, moon facies, osteoporosis, hypertension

44. Ovarian Hormones • Paired pelvic organs on each side of the uterus • Hormones: • Estrogen • Made by follicle cells • Progesterone • Made by corpus luteum • Inhibin • Made by corpus luteum

45. Ovarian Hormones • Estrogen • Promotes ova maturation in follicles • Stimulates endometrial blood vessel growth • Development of secondary sex characteristics • Breast & uterine growth • Epiphyseal disc closure in long bones • Fat deposition in hips and thighs • Effects on brain, heart, blood vessels

46. Ovarian Hormones • Progesterone • Promotes glycogen storage • Growth of vessels in endometrium • Secretory cells in mammary glands develop • Inhibin • Decreases FSH and GnRH secretion

47. Testicular Hormones • Paired organs located in scrotum • Make two hormones: • Testosterone • Steroid made by interstitial cells • Promotes sperm maturation • Development of secondary sex characteristics • Reproductive organ growth, growth of facial & body hair, larynx (voice deepens), muscle and epiphyseal closure • Inhibin (made by sustentacular cells)

48. Other Hormones • Melatonin • Made by pineal gland (in brain) & retina • Secretion varies with light exposure • Regulates sleep onset & duration • Leptin • Appetite-suppressing hormone made in adipose tissue • Prostaglandins

49. Other Hormones • Prostaglandins • Made by all cells from phospholipids in their membranes • Letter A through I designations • Numerous fuctions • Inflammation, pain mechanisms, blood clotting • Vasoconstriction & vasodilation • Uterine contraction, reproduction • Digestive secretions & nutrient metabolism

50. Mechanisms of Hormone Action • Specific receptor must be in a target organ for the hormone to bind there and for the target organ cells to respond • Locations of receptor proteins: • Cell membrane, cytoplasm, nucleus of the target cells