C H A P T E R 5

1. C H A P T E R 5 HORMONAL REGULATION OF EXERCISE

2. Learning Objectives w Learn the role of your endocrine system in maintaining homeostasis in the body during rest and acute physical activity. w Learn the difference between steroid and nonsteroid hormones and their actions within the body. w Discover the roles of hormones in regulating fat and carbohydrate metabolism. w Find out how hormones help keep your fluid levels in check and prevent dehydration.

3. Nervous vs. Endocrine Systems • They work in concert • Nervous system: quick, short-lived, and localized effects • Endocrine system: slow, longer-lasting, and generalized effects

4. Endocrine vs. Exocrine Systems w Endocrine system composed of endocrine glands—ductless glands that secrete hormones into the blood to affect distant cells and tissues w Exocrine glands secrete their products into ducts (e.g. sweat glands, salivary glands) w Pancreas has both functions: exocrine—digestive enzymes; endocrine—insulin and glucagon

5. Hormone • A chemical messenger secreted and stored in glandular tissues • Released into body fluids (blood or lymph) and circulate throughout the body • Affects target tissues/cells by binding to receptors wReceptors are specific to hormones so that only the correct hormone will “fit” the correct receptor—each cell has 2,000 to 10,000 specific receptors

6. How it works

7. ENDOCRINE ORGANS

8. Steroid Hormones w Lipid soluble (hydrophobic, or “water fearing”) w Diffuse easily through cell membranes; receptors located within cell (cytoplasm or nucleus) w Chemical structure is derived from or is similar to cholesterol w Secreted by adrenal cortex (e.g., cortisol, aldosterone), ovaries (e.g., estrogen/progesterone), testes (e.g., testosterone), placenta (e.g., estrogen/progesterone)

9. Action of a Steroid Hormone Powers and Howley, Exercise Physiology, 2004

10. Nonsteroid Hormones wWater soluble (hydrophilic, or “water loving”) w Cannot normally diffuse through cell membranes; receptors located on cell membrane that activate secondary intracellular pathways w Amino acid derivatives (e.g., epinephrine) and protein or peptide hormones (e.g., insulin)

11. Action of a Non-steroid Hormone Powers and Howley, Exercise Physiology, 2004

12. Control of Hormone Release w Plasma levels of specific hormones fluctuate. w Secretion is regulated by a negative feedback system. w Target cells can also alter their number of hormone receptors via down-regulation or up-regulation. Stimulus Gland Hormone

13. Alteration in Number of Receptors Down-regulation—Decrease in number of cell receptors; less hormone can bind to the cell to affect cell function; thus, decreased sensitivity to the hormone Up-regulation—Increase in number of cell receptors; more hormone can bind to the cell to affect cell function; thus, increased sensitivity to the hormone Receptors are proteins, so up-regulation involves increased receptor protein synthesis, and down-regulation involves decreased receptor protein synthesis

14. THE PITUITARY GLAND

15. Growth Hormone (Anterior Pituitary Gland) w Promotes long bone growth and muscle growth and hypertrophy by facilitating amino acid transport into muscle fibers w Cloned human growth hormone taken with anabolic steroids to stimulate muscle growth (illegal, of course) w Levels are elevated during aerobic exercise in proportion to exercise intensity – directly stimulates lipolysis (FFA release from triglycerides) Giantism – oversecretion during development Dwarfism – undersecretion Acromegaly – oversecretion in adulthood

16. Antidiuretic Hormone Response to Exercise Powers and Howley, Exercise Physiology,2004

17. HOW ADH CONSERVES BODY WATER

18. Mineralocorticoids wAldosterone maintains sodium balance in extracellular fluids Glucocorticoids • Maintain consistent plasma glucose levels between meals; anti-inflammatory and decreases sensation of pain Gonadocorticoids w Released in addition to those released by reproductive organs but in lesser amounts w Include androgens, estrogens, and progesterones Steroid Hormones of the Adrenal Cortex

19. RENIN-ANGIOTENSIN MECHANISM

20. PLASMA VOLUME AND ALDOSTERONE DURING CYCLING

21. Hormones of the Adrenal Medulla wCatecholamines — epinephrine and norepinephrine w Stimulated by sympathetic nervous system to prepare you for “fight or flight” – extremely important during exercise ►Increase rate and force of heart contraction, blood pressure, and respiration ►Increase metabolic rate, glycogenolysis, and release of glucose and FFA into blood ►Increase blood flow to the active skeletal muscles through redistribution of cardiac output, i.e., vasodilation of vessels in active muscles and vasoconstriction of vessels in inactive tissues (including muscles)

22. Catecholamine Receptors • Alpha- and beta-adrenergic receptors bind the catecholamines to exert the sympathetic effects in cells • - α1: • - β1: • - β2: • - β3:

23. Blood plasma catecholamine concentrations during exercise

24. Hormones of the Pancreas Insulin—secreted from pancreatic beta cells when plasma glucose levels are elevated (hyperglycemia), e.g., after eating; stimulates glucose uptake in muscle and fat cells - What happens to insulin levels during exercise? Glucagon—secreted from pancreatic alpha cells when plasma glucose concentrations are below normal (hypoglycemia), e.g., during prolonged exercise

25. Insulin

26. PLASMA LEVELS OF GLUCOSE AND INSULIN DURING CYCLING AT 65% TO 75% VO2MAX .

27. Hormonal Changes that Increase Blood Glucose during Exercise 1. Increases in epinephrine 2. Increases in norepinephrine 3. Increases in glucagon 4. Decreases in insulin 5. Increases in cortisol Remember: the concentration of glucose in the blood is a result of the balance between the rate of glucose appearance and the rate of glucose disappearance

28. BLOOD GLUCOSE LEVELS AFTER SPRINTING

29. Hormonal Control of Fat Breakdown When carbohydrate reserves are low, hormones accelerate the oxidation of fats to ensure your muscles get the energy they need. The rate of triglyceride breakdown into FFA and glycerol partly determines the rate at which muscles use fat as a fuel source during exercise.

30. Hormones Increasing Triglyceride Breakdown into FFA w Increases in cortisol w Increases in epinephrine w Increases in norepinephrine • Decreases in insulin • These hormones have a role in the activation of lipases, including HSL.

31. Hormonal Effects on Fuel Metabolism

32. Hormonal Effects on Fuel Metabolism

33. PLASMA LEVELS OF HORMONES DURING CYCLING AT 65% VO2MAX .

34. PLASMA LEVELS OF FFA AND CORTISOL DURING CYCLING AT 65% TO 75% VO2MAX .

35. PLASMA LEVELS OF EPINEPHRINE, NOREPINEPHRINE, GH, AND FFA DURING CYCLING AT 65% TO 75% VO2MAX .

36. Triiodothyronine (T3) and Thyroxine (T4) w Increase protein and enzyme synthesis w Increase size and number of mitochondria in cells w Promote rapid cellular uptake of glucose w Enhance glycolysis and glycogenesis w Increase FFA availability for oxidation Calcitonin w Decreases plasma calcium concentration w Acts primarily on bones and kidneys Hormones of the Thyroid Gland (Hypothyroidism; hyperthyroidism)

37. Parathyroid Hormone (Parathyroid Gland) The parathyroid gland produces parathyroid hormone (PTH), which regulates plasma calcium and plasma phosphate concentrations by targeting the bones, intestines, and kidneys.

38. Kidney: Erythropoietin and Renin The kidneys produce a hormone called erythropoietin, which regulates red blood cell (erythrocyte) production by stimulating bone marrow cells. This hormone is important in our adaptation to training and to altitude by increasing the number of RBCs and thus, the oxygen-carrying capacity of the blood. The kidneys also release renin, an enzyme that initiates the cascade resulting in aldosterone release, for blood pressure control and fluid and electrolyte balance.