exercise physiology chapter 5 hormones
• Anterior Pituitary Gland
- Adrenocorticotropic hormone (ACTH) - Follicle-stimulating hormone (FSH) - Luteinizing hormone (LH) - Melanocyte-stimulating hormone (MSH) - Thyroid-stimulating hormone (TSH) - Growth hormone (GH) - Prolactin
• Hormones
- Alter the activity of tissues that possess receptors to which the hormone can bind - Several classes based on chemical makeup § Amino acid derivatives § Peptides/protein § Steroids
• Hypothalamus
- Controls secretions from pituitary gland • Stimulates release of hormones from anterior pituitary gland - Releasing hormones or factors • Provides hormones for release from posterior pituitary gland
• Downregulation
- Decrease in receptor number in response to high concentration of hormone
•Neuroendocrine system
- Endocrine system releases hormones - Nervous system uses neurotransmitters
• Hormones are secreted from endocrine gland
- Hypothalamus and pituitary glands - Thyroid and parathyroid glands - Adrenal glands - Pancreas - Testes and ovaries
• Upregulation
- Increase in receptor number in response to low concentration of hormone
• Posterior Pituitary Gland
- Oxytocin - Antidiuretic hormone (ADH)
• Endocrine glands
- Release hormones directly into the blood
In Summary part 5
The adrenal cortex secretes aldosterone (mineralcorticoid), cortisol (glucocorticoid), and estrogens and androgens (sex steroids). § Aldosterone regulates Na+ and K+ balance. Aldosterone secretion increases with strenuous exercise, driven by the renin-angiotensin system. § Cortisol responds to a variety of stressors, including exercise, to ensure that fuel (glucose and free fatty acids) is available, and to make amino acids available for tissue repair
Control of Cortisol Secretion
mobilizes tissue amino acids mobilizes free fatty acids stimulates gluconeogenesis blocks entry of glucose into tissue
In Summary part 9
§ Glucose is taken up seven to twenty times faster during exercise than at rest—even with the decrease in plasma insulin. The increases in intracellular Ca+2 and other factors are associated with an increase in the number of glucose transporters that increase the membrane transport of glucose. § Training causes a reduction in E, NE, glucagon, and insulin responses to exercise.
In Summary- part 7
§ Glycogen breakdown to glucose in muscle is under the dual control of epinephrine-cyclic AMP and Ca+2-calmodulin. The latter's role is enhanced during exercise due to the increase in Ca+2 from the sarcoplasmic reticulum. In this way, the delivery of fuel (glucose) parallels the activation of contraction.
In Summary part 6
§ Insulin is secreted by the bcells of the islets of Langerhans in the pancreas and promotes the storage of glucose, amino acids, and fats. § Glucagon is secreted by the acells of the islets of Langerhans in the pancreas and promotes the mobilization of glucose and fats.
In Summary part 9
§ Plasma glucose is maintained during exercise by increasing liver glycogen mobilization, using more plasma FFA, increasing gluconeogenesis, and decreasing glucose uptake by tissues. The decrease in plasma insulin and the increase in plasma E, NE, GH, glucagon, and cortisol during exercise control these mechanisms to maintain the glucose concentration.
In Summary part 7
§ Testosterone and estrogen establish and maintain reproductive function and determine secondary sex characteristics. § Chronic exercise (training) can decrease testosterone levels in males and estrogen levels in females. The latter adaptation has potentially negative consequences related to osteoporosis.
In Summary part 4
§ The adrenal medulla secretes the catecholamines epinephrine (E) and norepinephrine (NE). E is the adrenal medulla's primary secretion (80%), while NE is primarily secreted from the adrenergic neurons of the sympathetic nervous system. § Epinephrine and norepinephrine bind to a-and b-adrenergic receptors and bring about changes in cellular activity (e.g., increased heart rate, mobilization of fatty acids from adipose tissue) via second messengers.
In Summary part 1
§ The hormone-receptor interaction triggers events at the cell; changing the concentration of the hormone, the number of receptors on the cell, or the affinity of the receptor for the hormone will all influence the magnitude of the effect. § Hormones bring about their effects by modifying membrane transport, activating/suppressing genes to alter protein synthesis, and activating second messengers (cyclic AMP, Ca++, inositol triphosphate, and diacylglycerol)
in summary part 8
§ The hormones thyroxine, cortisol, and growth hormone act in a permissive manner to support the actions of other hormones during exercise. § Growth hormone and cortisol also provide a "slow-acting" effect on carbohydrate and fat metabolism during exercise.
In Summary part 2
§ The hypothalamus controls the activity of both the anterior pituitary and posterior pituitary glands. § GH is released from the anterior pituitary gland and is essential for normal growth. § GH increases during exercise to mobilize free fatty acids from adipose tissue and to aid in the maintenance of blood glucose
In Summary part 10
§ The plasma FFA concentration decreases during heavy exercise even though the adipose cell is stimulated by a variety of hormones to increase triglyceride breakdown to FFA and glycerol. This may be due to: § (a) the higher H+ concentration inhibiting hormone sensitive lipase, § (b) the high levels of lactate during heavy exercise promoting the resynthesisof triglycerides, § (c) an inadequate blood flow to adipose tissue, or § (d) insufficient albumin needed to transport the FFA in the plasma.
In Summary part 3
§ Thyroid hormones T3 and T4 are important for maintaining the metabolic rate and allowing other hormones to bring about their full effect.
Thyroid Hormones
• Act in a permissive manner to allow other hormones to exert their full effect - T3 enhances effect of epinephrine to mobilize free fatty acids from adipose tissue • No real change in T3 and T4 during exercise
Anterior Pituitary Gland
• Adrenocorticotropic hormone (ACTH) - Stimulates cortisol release form adrenal glands • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH) - Stimulates production of testosterone and estrogen • Melanocyte-stimulating hormone (MSH) • Thyroid-stimulating hormone (TSH) - Controls thyroid hormone release from thyroid gland • Prolactin • Growth hormone (GH
Mechanisms of Hormone Action
• Altering membrane transport - Insulin • Altering activity of DNA to modify protein synthesis - Steroid hormones • Activating second messengers via G protein - Cyclic AMP - Ca+2 - Inositol triphosphate - Diacylglycerol • Tyrosine Kinase - Insulin and growth hormone
Pancreas
• Both exocrine and endocrine functions • Secretes: - Insulin (from bcells) § Promotes the storage of glucose, amino acids, and fats § Lack of insulin is called diabetes mellitus - Glucagon (from acells) § Promotes the mobilization of fatty acids and glucose - Somatostatin (from dcells) § Controls rate of entry of nutrients into the circulation - Digestive enzymes and bicarbonate § Into the small intestine
Control of Muscle Glycogen Utilization
• Breakdown of muscle glycogen is under dual control - Epinephrine-cyclic AMP § Via b-adrenergic receptors - Ca+2-calmodulin § Enhanced during exercise due to Ca+2 release from sarcoplasmic reticulum • Evidence for role of Ca+2-calmodulin in glycogenolysis - Propranolol (b-receptor blocker) has no effect on muscle glycogen utilization
Aldosterone
• Control of Na+ reabsorption and K+ secretion - Na+/H2O balance •• Control of Na+ reabsorption and K+ secretion - Na+/H2O balance - Part of renin-angiotensin-aldosterone system - All three hormones increase during exercise • Stimulated by: - Increased K+ concentration - Decreased plasma volume
Ovaries
• Estrogen and Progesterone - Released from ovaries - Establish and maintain reproductive function - Levels vary throughout the menstrual cycle
Hormone-Substrate Interaction
• FFA mobilization dependent on hormone sensitive lipase (HSL) • FFA mobilization decreases during heavy exercise - This occurs in spite of persisting hormonal stimulation for FFA mobilization • May be due to: - High levels of lactic acid § Promotes resynthesis of triglycerides - Elevated H+ concentration inhibits HSL - Inadequate blood flow to adipose tissue - Insufficient albumin to transport FFA in plasma
Epinephrine and Norepinephrine
• Fast-acting hormones • Maintain blood glucose during exercise - Muscle glycogen mobilization - Increasing liver glucose mobilization - Increasing FFA mobilization - Interfere with 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 following training
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 - Protein synthesis is collagen, not contractile protein • Difficult to detect usage by athletes
Muscle Glycogen Utilization
• Glycogenolysis is related to exercise intensity - High-intensity exercise results in greater and more rapid glycogen depletion • Plasma epinephrine is a powerful simulator of glycogenolysis - High-intensity exercise results in greater increases in plasma epinephrine
Hormone-Receptor Interactions
• Hormones only affect tissue with specific receptors • Magnitude of effect dependent on: - Concentration of the hormone - Number of receptors on the cell - Affinity of the receptor for the hormone
Adipose Tissue Is an Endocrine Organ
• In addition to storing triglycerides, adipose tissue also secretes hormones - Leptin § Influences appetite through the hypothalamus § 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
Anabolic Steroids and Performance
• Initial studies showed no benefit for developing muscle mass - In contrast to real-world reports § "Subjects" used 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
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 and glucagon secretion influenced by catecholamines
cortisol
• Maintenance of plasma glucose - Promotes protein breakdown for gluconeogenesis - Stimulates FFA mobilization - Stimulates glucose synthesis - Blocks uptake of glucose into cells § Promotes the use of free fatty acids as fuel • Stimulated by: - Stress, via ACTH § Part of General Adaptation Syndrome - Exercise
Posterior Pituitary Gland
• Oxytocin • Antidiuretic hormone (ADH) - Reduces water loss from the body to maintain plasma volume § Favors reabsorption of water from kidney tubules to capillaries - Release stimulated by high plasma osmolality and low plasma volume § Due to sweat loss without water replacement - Increases during exercise >60% VO2 max § To maintain plasma volume
Parathyroid Gland
• Parathyroid hormone - Primary hormone in plasma Ca+2 regulation - Stimulates Ca+2 release from bone - Stimulates reabsorption of Ca+2 by kidneys - Converts vitamin D3 into a hormone that increase Ca+2 absorption from GI tract
Blood Glucose Homeostasis During Exercise
• Plasma glucose maintained through four processes: - Mobilization of glucose from liver glycogen stores - Mobilization of FFA from adipose tissue § Spares blood glucose - Gluconeogenesis from amino acids, lactic acid, and glycerol - Blocking the entry of glucose into cells § Forces use of FFA as a fuel • Controlled by hormones - Permissive or slow-acting - Fast-acting
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
Adrenal Medulla
• Secretes the catecholamines - Epinephrine (E) and norepinephrine (NE) § Fast-acting hormones § Part of "fight or flight" response - Bind to adrenergic receptors § Alpha (a) § Beta (b) - Effects depend on hormone used and receptor type
Growth Hormone
• Slow-acting hormone • Effects: - Supports the action of cortisol § Decreases glucose uptake by tissues § Increases free fatty acid mobilization § Enhances gluconeogenesis in the liver • Exercise effect - Increase in plasma GH with increased intensity - Greater response in trained runners
Cortisol
• Slow-acting hormone • Effects: - Stimulate FFA mobilization from adipose tissue - Enhance gluconeogenesis in the liver - Decrease the rate of glucose utilization by cells • Effect of exercise - Decrease during low-intensity exercise - Increase during high-intensity exercise § Above ~60% VO2 max • Changes in cortisol may be related to repair of exerciseinduced tissue damage
Thyroid Gland
• Stimulated by TSH • Triiodothyronine (T3) and thyroxine (T4) - Establishment of metabolic rate - Permissive hormones § Permit full effect of other hormones • Calcitonin - Regulation of plasma Ca+2 § Blocks release from bone, stimulates excretion by kidneys • Parathyroid Hormone - Primary hormone in plasma Ca+2 regulation § Stimulates release from bone, stimulates reabsorption by kidneys
Growth Hormone
• Stimulates release of insulin-like growth factors (IGFs) - IGF-1 in muscle responsible for muscle growth • 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
Testes
• Testosterone - Released from testes - Anabolic steroid § Promotes tissue (muscle) building § Performance enhancement - Androgenic steroid § Promotes masculine characteristic
Blood Hormone Concentration
• The effect of a hormone on a tissue is determined by the plasma concentration • Determined by: - Rate of secretion of hormone from endocrine gland § Magnitude of input § Stimulatory versus inhibitory input - Rate of metabolism or excretion of hormone § At the receptor and by the liver and kidneys - Quantity of transport protein § Steroid hormones - Changes in plasma volume