1. Chapter 33 THE ENDOCRINE SYSTEM

2. The endocrine system: ] interacts with the nervous system to maintain homeostasis. ] consists of endocrine glands & isolated cells that secrete hormones.

3. A. Hormones Chemicals synthesized in one part of an organism & transported to another, where they affect target cells. Target cells have receptors on or in them that bind only to certain hormones. Hormones Target cells

4. 1. Classes of Hormones ] Peptide hormones F water-soluble F bind to receptors on target cell’s surface ] Steroid hormones F lipid-soluble F bind to receptors in target cell’s cytoplasm or nucleus

5. 2. Hormone Regulation ] Positive feedback loop Accumulation of a certain biochemical stimulates an increase in its production. Ex. release of oxytocin during childbirth ] Negative feedback loop Accumulation of a certain biochemical stimulates a decrease in its production. Ex. release of most hormones

6. B. Diversity of Endocrine Systems All animals produce hormones. 1. Invertebrate Hormones Most are secreted by neurosecretory cells. Invertebrate hormones regulate: ] regeneration (Hydra, flatworms, annelids) ] color change (crustaceans) ] gonad maturation (flatworms, mollusks, arthropods) ] molting & metamorphosis (insects)

8. 2. Vertebrate Hormones Secreted by neurosecretory cells & endocrine glands. All vertebrates produce the same basic hormones, but may have different functions in different species. Ex. Thyroxine ] sets pace of metabolism in humans ] controls metamorphosis in frogs ] controls heat production & oxygen consumption in birds.

9. All vertebrate endocrine systems are regulated by the hypothalamus and the pituitary gland.

10. C. The Human Endocrine System Consists of neurosecretory cells, endocrine glands & scattered hormone-secreting cells.

11. 1. Pituitary Gland Anterior Pituitary (regulated by releasing & inhibiting hormones of hypothalamus)

12. ] Growth hormone (GH) F targets all cells  promotes growth & development Hyposecretion in children causes pituitary dwarfism. Hypersecretion in children causes pituitary gigantism. Hypersecretion in adults causes acromegaly. ] Prolactin F targets mammary glands  stimulates milk production

13. ] Follicle-stimulating hormone (FSH) F targets ovaries  initiates development of ovarian follicles, oocyte maturation, and release of estrogen F targets testes  promotes development of testes & production of sperm ] Luteinizing hormone (LH) F targets ovaries  stimulates ovulation F targets testes  stimulates production of testosterone

14. ] Thyroid-stimulating hormone (TSH) F targets thyroid gland  stimulates release of thyroxine & triiodothyronine ] Adrenocorticotropic hormone (ACTH) F targets adrenal cortex  stimulates release of glucocorticoids FSH, LH, TSH & ACTH are tropic hormones.

15. Intermediate lobe of pituitary (regulated by releasing & inhibiting hormones of hypothalamus) ] Melanocyte-stimulating hormone (MSH) F targets melanocytes in skin of many vertebrates  causes color changes Intermediate lobe is poorly developed in humans.

16. Posterior Pituitary (stores & releases hormones produced by hypothalamus) ] Antidiuretic hormone (ADH) F targets kidneys  stimulates reabsorption of water F targets blood vessels  regulates blood pressure ] Oxytocin F targets uterus  stimulates contraction F targets mammary glands  stimulates release of milk when baby nurses

17. 2. Thyroid Gland ] Thyroxine (T 4 ) & Triiodothyronine (T 3 ) F target all cells of body  increase metabolic rate Dietary iodine is required to produce these two hormones. How does the body respond to a lack of iodine in diet? Why is iodine-deficient goiter rarely encountered in the US today?

18. TRH = thyroid releasing hormone

19. Hyposecretion in infants causes cretinism. - physical & mental retardation Hyposecretion in adults causes myxedema. - low metabolic rate, weight gain, lethargy, puffy face Hypersecretion causes hyperthyroidism. - high metabolic rate, weight loss, irritability, elevated blood pressure ] Calcitonin F targets bones, kidneys & intestines  reduces level of calcium in blood

20. 3. Parathyroid Glands ] Parathyroid hormone (PTH) F targets bones, kidneys & intestines  increases level of calcium in blood Calcitonin & PTH are antagonistic - interact to maintain normal blood calcium levels. Regulation of blood calcium level

21. 4. Adrenal Glands Adrenal Medulla ] Epinephrine & Norepinephrine F target heart, blood vessels, muscles, liver  increase heart rate, breathing rate, blood glucose  redirect blood flow toward brain & muscles Epinephrine & norepinephrine help body cope with emergencies (“fight-or-flight” response).

22. Adrenal Cortex ] Mineralocorticoids (aldosterone) F targets kidneys  retains sodium ions & water (increases blood volume/pressure) ] Glucocorticoids (cortisol) F targets all cells  increases glucose synthesis & suppresses immune system Mineralocorticoids & Glucocorticoids help body cope with long term stress.

23. Hyposecretion of adrenal cortex hormones causes Addison’s disease. - dehydration, low blood pressure, mental fatigue, weakness, impaired resistance to stress, darkening of skin Hypersecretion of adrenal cortex hormones causes Cushing’s disease. - redistribution of body fat, depresses immune system

24. 5. Pancreas Classified as exocrine & endocrine gland. ] Endocrine portion (islets of Langerhans) secretes hormones. ] Exocrine portion secretes digestive enzymes.

25. ] Insulin (secreted by beta cells of islets) F targets all cells  decreases blood glucose levels [stimulates conversion of glucose to glycogen] ] Glucagon (secreted by alpha cells of islets) F targets all cells  increases blood glucose levels [stimulates breakdown of glycogen to glucose] Insulin & Glucagon are antagonistic - interact to maintain normal blood glucose levels.

27. Diabetes mellitus Blood glucose level is too HIGH. Type I (insulin-dependent) F autoimmune disease - immune system destroys beta cells F usually develops during childhood F treated with daily injections of insulin Type II (insulin-independent) F defective insulin receptors F usually develops in adulthood F treated with diet & exercise

28. Gestational diabetes F temporary - develops during pregnancy F placental hormones interfere with insulin action Hypoglycemia Blood glucose level is too LOW. F excess insulin production F treated by following diet of frequent, small meals low in carbohydrates & high in protein

29. 6. Gonads Ovaries ] Estrogen F targets most cells  develops & maintains sexual characteristics in females; stimulates growth of uterine lining ] Progesterone F targets uterus  stimulates growth of uterine lining; maintains pregnancy

30. Testes ] Testosterone F targets most cells  develops & maintains sexual characteristics in males; promotes sperm formation ] Inhibin F targets anterior pituitary  inhibits FSH release (decreases sperm formation)