PowerLecture: Chapter 15

1. PowerLecture:Chapter 15 The Endocrine System

2. Learning Objectives • Know the general mechanisms by which molecules integrate and control the various metabolic activities in organisms. • Understand how the neuro-endocrine center controls secretion rates of other endocrine glands and responses in nerves and muscles. • Know the major endocrine glands and their secretions.

3. Learning Objectives (cont’d) • Know how sugar levels are regulated by hormones. • Differentiate the modes of action of steroid and nonsteroid hormones.

4. Impacts/Issues Hormones in the Balance

5. Hormones in the Balance • Arsenic may be an endocrine disrupter, especially of glucocorticoids. • Glucocorticoids in turn regulate genes that protect against cancer. • This may be the link between the consumption of arsenic in water supplies and increased rates of bladder, lung, and skin cancers.

6. Hormones in the Balance • Other endocrine disrupters are also coming under scrutiny. • The herbicide atrazine has been widely used on crops and turf grasses. • PCBs, used for many years as fluid insulation in electrical transformers, have been banned but still persist in the environment, where they are linked to reproductive disorders in humans and animals. • Research is continuing on endocrine disrupters; the jury is still out.

7. Useful References for Impacts/Issues The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • EPA: Endocrine Disruptors Research Initiative • InfoTrac: New Report Points Up Growing Evidence of Endocrine Disrupters. European Report, May 4, 2006.

8. How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu. • Some pesticides may disrupt hormone function in humans and other animals. Should they remain in use while researchers study their safety? • a. No, they could be dangerous; until we know for sure, it is better to be safe than sorry. • b. Yes, banning them because of potential harm isn't fair; there should be solid evidence first.

9. Useful References for How Would You Vote? The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Endocrine Disruption Study on Atrazine Disputed. Pesticide & Toxic Chemical News, Jan. 13, 2003. • Water Conserve 2.0: Chemical Affecting Frogs’ Sexuality; Males Are Acquiring Female Attributes after Exposure to a Common Weedkiller, Study Says

10. Section 1 The Endocrine System: Hormones

11. The Endocrine System: Hormones • Hormones are signaling molecules that are carried in the bloodstream. • Signaling molecules are hormones and secretions that can bind to target cells and elicit in them a response. • Hormones are secreted by endocrine glands, endocrine cells, and some neurons. • Local signaling molecules are released by some cells; these work only on nearby tissues. • Pheromones are signaling molecules that have targets outside the body and which are used to integrate behaviors.

12. The Endocrine System: Hormones • Hormone sources: The endocrine system. • The sources of hormones (hormone producing glands, cells, and organs) may be collectively called the endocrine system. • Endocrine sources and the nervous system function in highly interconnected ways.

13. The Endocrine System: Hormones • Hormones often interact. • In an opposing interaction the effect of one hormone opposes the effect of another. • In a synergistic interaction the combined action of two or more hormones is necessary to produce the required effect on target cells. • In a permissive interaction one hormone exerts its effect only when a target cell has been “primed” to respond by another hormone.

14. Animation: Major Human Endocrine Glands CLICKTO PLAY

15. Fig. 15.1a, p. 271 hypothalamus pineal gland pituitary gland thyroid gland parathyroid glands thymus gland adrenal glands pancreatic islets ovaries testes

16. Useful References for Section 1 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Review of the Endocrine System. Deirdre G. Bauer. MedSurg Nursing, Oct. 2005.

17. Section 2 Types of Hormones and Their Signals

18. Types of Hormones and Their Signals • Hormones come in several chemical forms. • Steroid hormones are lipids made from cholesterol. • Amine hormones are modified amino acids. • Peptide hormones are peptides of only a few amino acids. • Protein hormones are longer chains of amino acids.

19. Types of Hormones and Their Signals • All hormones bind target cells; this signal is converted into a form that works in the cell to change activity. • A target cell’s response to a hormone is dependent on two factors: • Different hormones activate different cellular response mechanisms. • Not all cells have receptors for all hormones; the cells that respond are selected by means of the type of receptor they possess.

20. Types of Hormones and Their Signals • Steroid hormones interact with cell DNA. • Steroid hormones, such as estrogen and testosterone, are lipid-soluble and therefore cross plasma membranes readily. • Once inside the cell, they penetrate the nuclear membrane and bind to receptors in the nucleus, either turning on or turning off genes. • Switching genes on or off changes the proteins that are made by the cell, thus effecting a response. • Some steroid hormones bind receptors in the cell membrane and change membrane properties to affect change to the target cell’s function.

21. Fig. 15.2a, p. 273 1 A steroid hormone molecule moves from the blood into the fluid that bathes a target cell. 2 Being a lipid-soluable molecule, the steroid hormone diffuses across the target cell’s plasma membrane. 3 The hormone diffuses through the cytoplasm, then on through the nuclear envelope. Inside the nucleus, it will bind with a receptor molecule. 5 In the cytoplasm, the resulting protein carries out the cell’s response to the hormone signal. receptor 4 Now the hormone-receptor complex triggers gene activity in the DNA hormone-receptor complex change in cell activity

22. Video: Mechanism of a steroid hormone CLICKTO PLAY

23. Types of Hormones and Their Signals • Nonsteroid hormones act indirectly, by way of second messengers. • Nonsteroid hormones include the amine, peptide, and protein hormones. • Nonsteroid hormones cannot cross the plasma membrane of target cells, so they must first bind to a receptor on the plasma membrane. • Binding of the hormone to the receptor activates the receptor; it in turn stimulates the production of a second messenger, a small molecule that can relay signals in the cell. • Cyclic AMP (cyclic adenosine monophosphate) is one example of a second messenger.

24. 1 A glucagon molecule diffuses from blood into the fluid that bathes the plasma membrane of a liver cell. glucagon receptor at target cell’s membrane + Pi cyclic AMP ATP 2 Glucagon binds with the receptor, and the binding activates adenylate cyclase. This enzyme catalyzes the formation of cyclic AMP inside the target cell. 3 The cyclic AMP now activates protein kinase A. 4 Protein kinase A converts phosphorylase kinase to active form. This enzyme activates a different enzyme, which breaks down glycogen to its glucose monomers. 5 Protein kinase A also inhibits an enzyme required for glycogen synthesis. Fig. 15.2b, p. 273

25. Video: Mechanism of a peptide hormone CLICKTO PLAY

26. Useful References for Section 2 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Can PYY Cure Obesity? U.S. News & World Report, Sept. 15, 2003.

27. Section 3 The Hypothalamus and Pituitary Gland: Major Controllers

28. The Hypothalamus and Pituitary Gland • The hypothalamus and pituitary gland work jointly as the neural-endocrine control center. • The hypothalamus is a portion of the brain that monitors internal organs and conditions. • The pituitary is connected to the hypothalamus by a stalk. • The posterior lobe consists of nervous tissue and releases two hormones made in the hypothalamus. • The anterior lobe makes and secretes hormones that control the activity of other endocrine glands.

29. Fig. 15.1b, p. 271 hypothalamus optic chasma Location of the pituitary gland: pituitary stalk anterior lobe posterior lobe membrane around brain

30. The Hypothalamus and Pituitary Gland • The posterior pituitary lobe produces ADH and oxytocin. • Neurons in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin, which are released from axon endings in the capillary bed of the posterior lobe. • ADH (or vasopressin) acts on the walls of kidney tubules to control the body’s water and solute levels by stimulating reabsorption. • Oxytocin triggers uterine muscle contractions to expel the fetus and acts on mammary glands to release milk.

31. Animation: Posterior Pituitary Function CLICKTO PLAY

32. a Secretory neurons in the hypothalamus synthesize ADH or oxytocin. b The ADH Oxytocin moves downward inside the axons of the secretory neurons and accumulates in the axon endings. d The hormone molecules move into the general circulation. c Action potentials trigger the release of these hormones, which enter blood capillaries in the posterior lobe of the pituitary. oxytocin ADH kidney nephrons muscles in uterus wall mammary glands Fig. 15.3, p. 274

33. The Hypothalamus and Pituitary Gland • The anterior pituitary lobe produces six other hormones. • Corticotropin (ACTH) stimulates the adrenal cortex. • Thyrotropin (TSH) stimulates the thyroid gland. • Follicle-stimulating hormone (FSH) causes ovarian follicle development and egg production.

34. The Hypothalamus and Pituitary Gland • Luteinizing hormone (LH) also acts on the ovary to release an egg. • Prolactin (PRL) acts on the mammary glands to stimulate and sustain milk production. • Somatotropin (STH), also known as growth hormone (GH), acts on body cells in general to promote growth. • Most of these hormones are releasers that stimulate target cells to secrete other hormones; other hormones from the hypothalamus are inhibitors and block secretions.

35. Animation: Anterior Pituitary Function CLICKTO PLAY

36. Fig. 15.4, p. 275 a Cell bodies of different secretory neurons in the hypothalamus secrete releasing and inhibiting hormones. b The hormones are picked up by a capillary bed at the base of the hypothalamus. c The bloodstream delivers hormones to a capillary bed in the anterior lobe of pituitary. e Hormones from anterior lobe cells enter small blood vessels that lead to the general circulation. d Molecules of the releasing or inhibiting hormone diffuse out of capillaries and act on endocrine cells in the anterior lobe. ACTH TSH FSH LH PRL STH(GH) most cells (growth-promoting effects) thyroid gland adrenal glands mammary glands testes in males, ovaries in females

38. Video: Hypothalamus and Pituitary CLICKTO PLAY

39. Useful References for Section 3 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • The Pituitary Society • InfoTrac: The Scent of Trust. Prevention, Oct. 2005.

40. Section 4 Factors That Influence Hormone Effects

41. Factors That Influence Hormone Effects • Problems with control mechanisms can result in skewed hormone signals. • Endocrine glands in general only release small quantities of hormones and control the frequency of release to make sure there isn’t too much or too little hormone.

42. Factors That Influence Hormone Effects • Abnormal quantities of hormones can lead to growth problems. • Gigantism results from an oversecretion of growth hormone in childhood. • Pituitary dwarfism results from an undersecretion of GH. Figures 15.5a and 15.14

43. Factors That Influence Hormone Effects • Acromegaly is a condition resulting from an oversecretion of GH in adulthood leading to abnormal thickening of tissues. • Diabetes insipidus occurs when ADH secretions fall or stop, leading to dilute urine and the possibility of serious dehydration. Figure 15.5b

44. Factors That Influence Hormone Effects • Hormone interactions, feedback, and other factors also influence a hormone’s effects. • At least four factors influence the effects of any given hormone. • Hormones often interact with one another. • Negative feedback mechanisms control secretion of hormones. • Target cells may react differently to hormones at different times. • Environmental cues can affect release of hormones. • Hormones throughout the body are affected in similar ways.

46. Video: Hormone Replacement Therapy • This video clip is available in CNN Today Videos for Anatomy & Physiology, 2003, Volume VII. Instructors, contact your local sales representative to order this volume, while supplies last.

47. Useful References for Section 4 The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: Acromegaly. Ana Pokrajac-Simeunovic and Peter Trainer. Chemist & Druggist, Nov. 19, 2005.

48. Section 5 The Thymus, Thyroid, and Parathyroid Glands

49. The Thymus, Thyroid, and Parathyroid Glands • Thymus gland hormones aid immunity. • Thyroid hormones affect metabolism, growth, and development. • The thyroid gland secretes thyroid hormone (TH), which has effects on metabolism, growth, and development; the thyroid gland also secretes calcitonin, which helps regulate calcium levels in the blood.

50. Fig. 15.6a, p. 278 thyroid cartilage (Adam’s apple) blood vessel thyroid gland trachea (windpipe)