Hormonal Regulation of Metabolism During Exercise

1. Hormonal Control During Exercise

3. Endocrine Glands and Their Hormones • Several endocrine glands in body; each may produce more than one hormone • Hormones regulate physiological variables during exercise

4. Hormonal Regulation of Metabolism During Exercise • Major endocrine glands responsible for metabolic regulation • Anterior pituitary gland • Thyroid gland • Adrenal gland • Pancreas • Hormones released by these glands affect metabolism of carbohydrate and fat during exercise

5. Endocrine Regulation of Metabolism:Anterior Pituitary Gland • Pituitary gland attached to inferior hypothalamus • Three lobes: anterior, intermediate, posterior • Secretes hormones in response to hypothalamic hormone factors • Releasing factors, inhibiting factors • Exercise  secretion of all anterior pituitary hormones

6. Endocrine Regulation of Metabolism:Anterior Pituitary Gland • Releases growth hormone (GH) • Potent anabolic hormone • Builds tissues, organs • Promotes muscle growth (hypertrophy) • Stimulates fat metabolism • GH release proportional to exercise intensity

7. Endocrine Regulation of Metabolism:Thyroid Gland • Secretes triiodothyronine (T3), thyroxine (T4) • T3 and T4 lead to increases in • Metabolic rate of all tissues • Protein synthesis • Number and size of mitochondria • Glucose uptake by cells • Rate of glycolysis, gluconeogenesis • FFA mobilization

8. Endocrine Regulation of Metabolism:Thyroid Gland • Anterior pituitary releases thyrotropin • Also called thyroid-stimulating hormone (TSH) • Travels to thyroid, stimulates T3 and T4 • Exercise increases TSH release • Short term: T4 (delayed release) • Prolonged exercise: T4 constant, T3

9. Endocrine Regulation of Metabolism:Adrenal Medulla • Releases catecholamines (fight or flight) • Epinephrine 80%, norepinephrine 20% –  Exercise   sympathetic nervous system   epinephrine and norepinephrine • Catecholamine release increases • Heart rate, contractile force, blood pressure – Glycogenolysis, FFA • Blood flow to skeletal muscle

10. Endocrine Regulation of Metabolism:Adrenal Cortex • Releases corticosteroids • Glucocorticoids • Also, mineralocorticoids, gonadocorticoids • Major glucocorticoid: cortisol –  Gluconeogenesis –  FFA mobilization, protein catabolism • Anti-inflammatory, anti-immune

11. Endocrine Regulation of Metabolism:Pancreas • Insulin: lowers blood glucose • Counters hyperglycemia, opposes glucagon –  Glucose transport into cells –  Synthesis of glycogen, protein, fat – Inhibits gluconeogenesis • Glucagon: raises blood glucose • Counters hypoglycemia, opposes insulin –  Glycogenolysis, gluconeogenesis

12. Regulation of Carbohydrate Metabolism During Exercise • Glucose must be available to tissues • Glycogenolysis (glycogen  glucose) • Gluconeogenesis (FFAs, protein  glucose)

13. Regulation of Carbohydrate Metabolism During Exercise • Adequate glucose during exercise requires • Glucose release by liver • Glucose uptake by muscles • Hormones that  circulating glucose • Glucagon • Epinephrine • Norepinephrine • Cortisol

14. Regulation of Carbohydrate Metabolism During Exercise • Circulating glucose during exercise also affected by • GH:  FFA mobilization,  cellular glucose uptake • T3, T4:  glucose catabolism and fat metabolism • Amount of glucose released from liver depends on exercise intensity, duration

15. Regulation of Carbohydrate Metabolism During Exercise • As exercise intensity increases – Catecholamine release  – Glycogenolysis rate  (liver, muscles) • Muscle glycogen used before liver glycogen • As exercise duration increases • More liver glycogen utilized –  Muscle glucose uptake   liver glucose release • As glycogen stores , glucagon levels 

16. Figure 4.4

17. Regulation of Carbohydrate Metabolism During Exercise • Glucose mobilization only half the story • Insulin: enables glucose uptake in muscle • During exercise • Insulin concentrations  • Cellular insulin sensitivity  • More glucose uptake into cells, use less insulin

18. Figure 4.5

19. Regulation of Fat Metabolism During Exercise • FFA mobilization and fat metabolism critical to endurance exercise performance • Glycogen depleted, need fat energy substrates • In response, hormones accelerate fat breakdown (lipolysis) • Triglycerides  FFAs + glycerol • Fat stored as triglycerides in adipose tissue • Broken down into FFAs, transported to muscle • Rate of triglyceride breakdown into FFAs may determine rate of cellular fat metabolism

20. Regulation of Fat Metabolism During Exercise • Lipolysis stimulated by • (Decreased) insulin • Epinephrine • Norepinephrine • Cortisol • GH • Stimulate lipolysis via lipase

21. Hormonal Regulation of Fluid and Electrolytes During Exercise • During exercise, plasma volume , causing –  Hydrostatic pressure, tissue osmotic pressure –  Plasma water content via sweating –  Heart strain,  blood pressure • Hormones correct fluid imbalances • Posterior pituitary gland • Adrenal cortex • Kidneys

22. Hormonal Regulation of Fluid and Electrolytes: Posterior Pituitary • Posterior pituitary • Secretes antidiuretic hormone (ADH), oxytocin • Produced in hypothalamus, travels to posterior pituitary • Secreted upon neural signal from hypothalamus • Only ADH involved with exercise –  Water reabsorption at kidneys • Less water in urine, antidiuresis

23. Hormonal Regulation of Fluid and Electrolytes: Posterior Pituitary • Stimuli for ADH release –  Plasma volume = hemoconcentration =  osmolality –  Osmolality stimulates osmoreceptors in hypothalamus • ADH released, increasing water retention by kidneys • Minimizes water loss, severe dehydration

24. Hormonal Regulation of Fluid and Electrolytes: Adrenal Cortex • Adrenal cortex • Secretes mineralocorticoids • Major mineralocorticoid: aldosterone • Aldosterone effects –  Na+ retention by kidneys –  Na+ retention   water retention via osmosis –  Na+ retention   K+ excretion

25. Hormonal Regulation of Fluid and Electrolytes: Adrenal Cortex • Stimuli for aldosterone release –  Plasma Na+ –  Blood volume, blood pressure –  Plasma K+ • Also indirectly stimulated by  blood volume,  blood pressure in kidneys

26. Hormonal Regulation of Fluid and Electrolytes: Kidneys • Kidneys • Target tissue for ADH, aldosterone • Secrete erythropoietin (EPO), renin • EPO • Low blood O2 in kidneys  EPO release • Stimulates red blood cell production • Critical for adaptation to training, altitude

27. Hormonal Regulation of Fluid and Electrolytes: Kidneys • Stimulus for renin (enzyme) release •  Blood volume,  blood pressure • Sympathetic nervous system impulses • Renin-angiotensin-aldosterone mechanism • Renin: converts angiotensinogen  angiotensin I • ACE: converts angiotensin I  angiotensin II • Angiotensin II stimulates aldosterone release

28. Figure 4.8

29. Figure 4.9

30. Hormonal Regulation of Fluid and Electrolytes: Osmolality • Osmolality • Measure of concentration of dissolved particles (proteins, ions, etc.) in body fluid compartments • Normal value: ~300 mOsm/kg • Osmolality and osmosis • If compartment osmolality , water drawn in • If compartment osmolality , water drawn out

31. Hormonal Regulation of Fluid and Electrolytes: Osmolality • Aldosterone and osmosis • Na+ retention   osmolality –  Osmolality   water retention • Where Na+ moves, water follows • Osmotic water movement minimizes loss of plasma volume, maintains blood pressure

32. Hormonal Regulation of Fluid and Electrolytes: Osmolality • ADH, aldosterone effects persist for 12 to 48 h after exercise • Prolonged Na+ retention  abnormally high [Na+] after exercise • Water follows Na+ • Prolonged rehydration effects