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Hormonal Response to Exercise

Hormonal Response to Exercise. 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

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Hormonal Response to Exercise

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  1. Hormonal Response to Exercise

  2. 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

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

  4. 1. 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)

  5. 2. Non-steroid 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)

  6. Hormone Secretion • Secreted in bursts • Plasma concentrations fluctuate over minutes/hours • Concentrations also fluctuate over days/weeks*What triggers or regulates hormone bursts? Secretion regulated by negative feedback

  7. Neuroendocrinology Blood Hormone Concentration Determined by: 1. Rate of secretion of hormone from endocrine gland • Magnitude of input • Stimulatory versus inhibitory input 2. Rate of metabolism or excretion of hormone • At the receptor and by the liver and kidneys 3. Quantity of transport protein • Steroid hormones 4. Changes in plasma volume

  8. Hormone Activity • Plasma concentration: • 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

  9. Hormone Receptors • Hormone effects are limited by 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

  10. 3. 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)

  11. 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

  12. 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

  13. Hormones: Regulation and Action Posterior Pituitary Gland • Antidiuretichormone (ADH) • Reduces water loss from the body to maintain plasma volume • Reabsorptionof water from kidney tubules to capillaries • Release stimulated by low plasma volume • Due to sweat loss without water replacement = less water in urine • Increases during exercise >60% VO2 max • To maintain plasma volume

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

  15. Hormones: Regulation and Action Growth Hormone • Essential growth of all tissues • Amino acid uptake and protein synthesis • Long bone growth • Spares plasma glucose • Reduces the use of plasma glucose • Increases gluconeogenesis • Mobilizes fatty acids from adipose tissue

  16. Hormonal Control of Substrate Mobilization During Exercise Growth Hormone • Slow-acting hormone • Exercise effect: • Increase in plasma GH with increased intensity • Greater response in trained runners *GH release proportional to exercise intensity

  17. Hormones: Regulation and Action Growth Hormone and Performance • GH increases protein synthesis in muscle and long bone growth • Used to treat childhood dwarfism • Also used by athletes and elderly • More adverse effects than benefits • No evidence that GH promotes strength gains • Difficult to detect usage by athletes

  18. 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

  19. Hormonal Control of Substrate Mobilization During Exercise Thyroid Hormones • Act in a permissive manner to allow other hormones to exert their full effect & maintain metabolic rate • T3 enhances effect of epinephrine to mobilize free fatty acids from adipose tissue • No significant change in T3 and T4 during exercise

  20. Hormones: Regulation and Action Thyroid Gland • Calcitonin • Regulation of plasma Ca+2  bone building • When Ca+2 levels are high = stimulates Ca+2 excretion by kidneys  expelled in urine • Protects against calcium loss from skeleton during periods of calcium mobilization  pregnancy & lactation

  21. Hormones: Regulation and Action Parathyroid Gland • Parathyroid hormone (opposes effects of calcitonin) • Primary hormone in plasma Ca+2 regulation • When Ca+2 levels are low = stimulates reabsorption of Ca+2 by kidneys

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

  23. Hormones: Regulation and Action Adrenal Cortex • Secretes steroid hormones • Derived from cholesterol • Mineralcorticoids • Aldosterone • Maintenance of plasma Na+ and K+ • Glucocorticoids • Cortisol • Regulation of plasma glucose • Sex steroids • Androgens and estrogens • Support prepubescent growth

  24. Hormones: Regulation and Action Cortisol • Maintenance of plasma glucose • Promotes protein breakdown for gluconeogenesis • Stimulates FFA mobilization from adipose tissue • Stimulates glucose synthesis • Blocks uptake of glucose into cells: Promotes use of free fatty acids as fuel • Stimulated by: • Stress • Exercise

  25. Hormonal Control of Substrate Mobilization During Exercise Cortisol • Slow-acting hormone • Effect of exercise: • Decrease during low-intensity exercise • Increase during high-intensity exercise • Above ~60% VO2 max

  26. Hormones: Regulation and Action Adipose Tissue Is an Endocrine Organ • In addition to storing triglycerides, adipose tissue also secretes hormones • Leptin • Influences appetite • Enhances insulin sensitivity and fatty acid oxidation • Adiponectin • Increases insulin sensitivity and fatty acid oxidation • With increased fat mass (obesity) • Higher leptin levels and lower adiponectin • Leads to type 2 diabetes and low-grade inflammation

  27. Hormones: Regulation and Action Testes and Ovaries • Testosterone • Released from testes • Anabolic steroid • Promotes tissue (muscle) building • Performance enhancement • Androgenic steroid • Promotes masculine characteristics • Estrogen and Progesterone • Released from ovaries • Establish and maintain reproductive function • Levels vary throughout the menstrual cycle

  28. Hormones: Regulation and Action Anabolic Steroids and Performance • Taken: 10 to 100 times the recommended dosage • Also associated with negative side effects • Revert to normal after discontinuation • Widespread use has led to testing of competitive athletes • Most users are not competitive athletes • Take more than one steroid in megadoses

  29. Hormones: Regulation and Action Pancreas • Both exocrine and endocrine functions • Secretes: • Insulin (from  cells) • Promotes the storage of glucose, amino acids, and fats • Lack of insulin is called diabetes mellitus • Glucagon (from  cells) • Promotes the mobilization of fatty acids and glucose • Somatostatin • Controls rate of entry of nutrients into the circulation • Digestive enzymes and bicarbonate • Into the small intestine

  30. 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

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

  32. 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

  33. 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

  34. 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 used –  Muscle glucose uptake   liver glucose release • As glycogen stores , glucagon hormone levels 

  35. Hormonal Control of Substrate Mobilization During Exercise Blood Glucose Homeostasis During Exercise • Plasma glucose maintained through four processes: 1. Mobilization of glucose from liver glycogen stores 2. Mobilization of FFA from adipose tissue • Spares blood glucose 3. Gluconeogenesisfrom amino acids, lactic acid, and glycerol 4. Blocking the entry of glucose into cells • Forces use of FFA as a fuel

  36. 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

  37. Hormonal Control of Substrate Mobilization During Exercise Role of insulin & Glucagon: Fast-Acting Hormones • Insulin • Uptake and storage of glucose and FFA • Plasma concentration decreases during exercise • Decreased insulin response following training • Glucagon • Mobilization of glucose and FFA fuels • Plasma concentration increases during exercise • Decreased response following training • Insulin & glucagon secretion influenced by catecholamines

  38. Hormonal Control of Substrate Mobilization During Exercise Epinephrine and Norepinephrine • Also Fast-acting hormones • Maintain blood glucose during exercise • Muscle glycogen mobilization • Increasing liver glucose mobilization • Increasing FFA mobilization • Alter glucose uptake • Plasma E and NE increase during exercise • Also related to increased heart rate and blood pressure during exercise • Decreased plasma E and NE after training

  39. Regulation of Fat Metabolism During Exercise • FFA mobilization and fat metabolism critical to endurance exercise performance • Glycogen depleted  need fat for energy = release 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 = determine rate of cellular fat metabolism

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

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