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Hormonal Control During Exercise

This chapter discusses the endocrine system, hormones and their actions, and the regulation of metabolism, fluid, and electrolytes during exercise. It explores the different types of hormones, their receptors, and how they are secreted and regulated. The role of hormone receptors and their actions in the body are also explained.

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Hormonal Control During Exercise

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  1. Chapter 4 • Hormonal Control During Exercise

  2. Chapter 4 Overview • Endocrine system • Hormones (types, receptors, actions) • Endocrine glands and their hormones • Hormonal regulation of metabolism during exercise • Hormonal regulation of fluid and electrolytes during exercise

  3. The Endocrine System • A communication system • Nervous system = electrical communication • Endocrine system = chemical communication • Slower responding, longer lasting than nervous system • Maintains homeostasis via hormones • Chemicals that control and regulate cell/organ activity • Act on target cells • Constantly monitors internal environment

  4. The Endocrine System • Coordinates integration of physiological systems during rest and exercise • Maintains homeostasis during exercise • Controls substrate metabolism • Regulates fluid, electrolyte balance

  5. Figure 4.1

  6. Hormones: Steroid Hormones • Derived from cholesterol • Lipid soluble, diffuse through membranes • Secreted by four major glands • Adrenal cortex (cortisol, aldosterone) • Ovaries (estrogen, progesterone) • Testes (testosterone) • Placenta (estrogen, progesterone)

  7. Hormones: Nonsteroid Hormones • Not lipid soluble, cannot cross membranes • Divided into two groups • Protein/peptide hormones • Most nonsteroid hormones • From pancreas, hypothalamus, pituitary gland, • Amino acid-derived hormones • Thyroid hormones (T3, T4) • Adrenal medulla hormones (epinephrine, norepinephrine)

  8. Hormone Secretion • Secreted in bursts (pulsatile) • Plasma concentrations fluctuate over minutes/hours • Concentrations also fluctuate over days/weeks • What triggers or regulates hormone bursts? • Secretion regulated by negative feedback • Hormone release causes change in body • High level of downstream change  secretion • Low level of downstream change  secretion • Example: home thermostat

  9. Hormone Activity • Plasma concentration can be poor indicator of hormone activity • Cells change sensitivity to hormones • Number of receptors on cell surface can change • Downregulation:  number of receptors during high plasma concentration = desensitization • Upregulation:  number of receptors during high plasma concentration = sensitization

  10. Hormone Receptors • Hormones limit scope of their effects by using hormone-specific receptors • No receptor on cell surface = no hormone effect • Hormone only affects tissues with specific receptor • Hormone exerts effects after binding with receptor • Typical cell has 2,000 to 10,000 receptors • Hormone binds to receptor: hormone–receptor complex

  11. Steroid Hormone Actions • Lipid soluble (can cross cell membranes) • Steroid hormone receptors found inside cell, in cytoplasm or nucleus • Hormone–receptor complex enters nucleus • Binds to DNA, direct gene activation • Regulates mRNA synthesis, protein synthesis

  12. Figure 4.2

  13. Nonsteroid Hormone Actions • Not lipid soluble (cannot cross cell membrane) • Receptors on cell membrane  second messengers • Carry out hormone effects • Intensify strength of hormone signal • Common second messengers • Cyclic adenosine monophosphate (cAMP) • Cyclic guanine monophosphate (cGMP) • Inositol triphosphate (IP3), diacylglycerol (DAG)

  14. Figure 4.3

  15. Hormones: Prostaglandins • Third class of (pseudo)hormones • Derived from arachidonic acid • Act as local hormones, immediate area • Inflammatory response (swelling, vasodilation) • Sensitize nociceptor free nerve endings (pain)

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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

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

  24. 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

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

  26. 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

  27. 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

  28. 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 

  29. Figure 4.4

  30. 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

  31. Figure 4.5

  32. 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

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

  34. 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

  35. 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

  36. 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

  37. Figure 4.6

  38. 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

  39. 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

  40. 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

  41. 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

  42. Figure 4.7

  43. Figure 4.8

  44. Figure 4.9

  45. 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

  46. 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

  47. 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

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