Hormones, Exercise, and Training PDF

Hormones, Exercise, And Training Metabolic pathways are regulated through the release of various hormones which stimulate or inhibit enzymes The Endocrine System - A communication system - Nervous system = electrical communication - Endocri...

Hormones, Exercise, And Training Metabolic pathways are regulated through the release of various hormones which stimulate or inhibit enzymes 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 - Coordinates integration of physiological systems during rest and exercise - Maintains homeostasis during exercise greater challenges to homeostasis during exercise - Controls substrate metabolism - Regulates fluid, electrolyte balance Endocrinology - Endocrine System - glands - Secrete “hormones” into blood stream - Functions (exercise) 1. Regulate growth 2. Regulate metabolic processes 3. Transporting substances through membranes (glucose) 4. Regulate water balance 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) 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) 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 decrease secretion - Low level of downstream change increase secretion - Example: Home thermostat Hormone Activity - Plasma concentration can be poor indicator of hormone activity - Cell sensitivity to hormones may change - Number of receptors on cell surface can change - Down-regulation: Decrease number of receptors during high plasma concentration = desensitization - Up-regulation: Increase number of receptors during high plasma concentration = sensitization Hormone Receptors - Hormones limit scope of their effects by using hormone-specific receptors on cells - 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 Non Steroid Hormone Actions - Not lipid soluble (cannot cross cell membrane) - Bind to specific receptors on cell membrane - Activate intracellular second messengers - Carry out hormone effects (relays signal)  - Also may intensify strength of the hormone signal - Common second messengers - Cyclic adenosine monophosphate (cAMP) - Cyclic guanine monophosphate (cGMP) - Inositol triphosphate (IP3), diacylglycerol (DAG), Ca2+ “Second Messenger” Mechanism - Ie- epinephrine, glucagon - Potential cAMP responses include: - Activation of cellular enzymes. - Change in membrane permeability - Promotion of protein synthesis - Change in cellular metabolism - Stimulation of cellular secretions Primary Roles During Exercise - Maintain Plasma Volume - Antidiuretic hormone (peptide) - Aldosterone (steroid) - Maintain Blood Glucose - Cortisol (steroid) - Glucagon (peptide) - Growth hormone (peptide) - Epinephrine (amine) - Norepinephrine (amine) - Insulin (peptide) Fluids And Electrolytes - During exercise, plasma volume decrease - Increase hydrostatic pressure, tissue osmotic pressure - Decrease plasma water content d/t sweating - = Increase heart strain, d/t decrease blood pressure and decrease SV - Hormones correct fluid and electrolyte imbalances - Posterior pituitary gland - Adrenal cortex - Kidneys Antidiuretic Hormone (ADH) (Vasopressin) Posterior Pituitary - ADH - Stimulated by:  - (Neural signal from hypothalamus) 1. Decrease plasma volume due to sweating 2. Increase concentration of blood (Increase osmolality ([ ] of dissolved substances)) 3. Exercise (esp. high intensity > 60% VO2max, heavy sweating, high temps) - Function 1. Decrease water loss from the body to maintain hydration (plasma vol.) 2. By increasing water reabsorption at the kidneys Aldosterone Adrenal Cortex Glands - Function - Regulates Na+ & K+ (electrolytes) & water concentration - Increase Na+ retention/reabsorption by kidneys - Stimuli for aldosterone release - Blood concentrations of Na+ and K+ - Decrease plasma Na+ - Increase plasma K+ - Also indirectly stimulated by â blood volume, â blood pressure in kidneys Hormonal Regulation of Fluid And Electrolytes: Kidneys - Stimulus for renin (enzyme) release - Decrease blood volume & decrease blood pressure in kidneys - Activated by sympathetic nervous system impulses - Renin-angiotensin-aldosterone mechanism - Renin: Converts angiotensinogen à angiotensin I - In lungs: Angiotensin-converting enzyme (ACE) - ACE: Converts angiotensin I à angiotensin II - Angiotensin II stimulates aldosterone release - Also causes vasoconstriction Blood Glucose Maintenance to Ensure Glucose Availability to Tissues - 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 - Increase liver glycogenolysis, gluconeogenesis - E and NE increase glucagon secretion and suppress insulin secretion Insulin (Pancreas) - Functions 1. Promotes storage of glucose, amino acids, & fats in cells - Inhibited by sympathetic system during exercise - Inhibition allows glucose release from liver & fat release from adipose cell - How does glucose get in the cell during exercise? - Exercise stimulates receptors on muscle cells to allow glucose to enter cell without insulin Altering Membrane Permeability - Insulin and GLUT-4 transporters enables glucose uptake in muscle - During exercise - Insulin concentrations decrease but cellular insulin receptor sensitivity increase - More glucose uptake into cells, at lower insulin concentrations - Important not to oppose other hormones releasing fuels - Exercise moves GLUT-4 transporters to the cell membrane independent of insulin via calcium involved in muscle contraction Glucagon (Pancreas) - Opposite effect of insulin - Insulin antagonist - Functions: - Helps maintain glucose levels during exercise - Promotes mobilization of fatty acids (from adipose tissue; lipolysis); - Glucose (from liver; glycogenolysis); gluconeogenesis Maintenance of Plasma Glucose During Exercise 1. Mobilization of glucose from liver glycogen stores (liver glycogenolysis) (glucagon, cortisol, epinephrine, & GH) 2. Mobilization of FFA from adipose tissue (lipolysis) - Glucagon, GH, epinephrine & cortisol (decreased insulin) - Spares blood glucose 3. Gluconeogenesis from amino acids, lactic acid, & glycerol (glucagon, cortisol, growth hormone, epinephrine) 4. Blocking entry of glucose into non-muscle cells - Cortisol (low intensity not much, high intensity large release) - Growth hormone - Forces use of FFA as a fuel Growth Hormone (Anterior Pituitary)  - Essential for normal growth (anabolism) - Stimulates protein synthesis (including muscle growth & long bone growth) - At rest - Stimulates uptake of A.A. & protein synthesis - Also stimulated by stress, low glucose levels, sleep, intense Growth Hormone During Exercise: Intensity - Increase during exercise (in proportion to intensity) - Helps maintain blood glucose - Mobilizes fatty acids from adipocyte - Promotes gluconeogenesis Epinephrine And Norepinephrine - Adrenal medulla - Catecholamines - Epinephrine (80%) & norepinephrine (20%) - Also called adrenalin - Fight or flight reflex - Released during exercise - Sympathetic nervous system Epinephrine - Effects on Body 1. Increase HR & contractility (­Increase BP) 2. Glycogenolysis, lipolysis, gluconeogenesis 3. Dilate bronchioles & blood vessels a. = increased respiration b. = increased blood flow to muscles - Plasma concentrations increase proportionally with exercise intensity, and significantly at - NorEpi > 50% VO2 max - Epi > 60-70% VO2 max Cortisol (Adrenal Cortex) - Stimulated by Stress (exercise, fasting, stress), peaks in morning - Functions during exercise: 1. Maintains plasma glucose (prevents it from dropping) a. Stimulates lipolysis b. Promotes protein breakdown for gluconeogenesis; decreases protein synthesis c. Blocks glucose from entering non-exercising tissues  - Suppresses immune system - Decreases bone formation Estrogen - Estrogen: group of hormones - Estradiol, estrone, estriol - Female characteristics - Estradiol may ↓ glycogen use and ↑ fat use - > knee laxity ↑ during menstruation - Higher HDL - Fat deposition - Muscle mass/strength - Female athlete triad - Amenorrhea Female Athlete Triad - Low energy availability - Irregular eating - Disordered eating - Menstrual dysfunction - Amenorrhea - Decrease bone mineral density (BMD) - Osteoporosis - Reduced energy deficit in sports (syndrome) (REDS) Testosterone - Both anabolic & androgenic hormone - Male characteristics - Stimulates protein synthesis - Research is equivocal on ↑ or ↓ during exercise - ↑ may be due to ↓ in plasma volume not ↑ in release - Testosterone receptors may be transiently upregulated - Prolonged endurance training may ↓, also seen with overtraining Anabolic Steroids And Performance - Therapeutic applications - Sports performance & body comp - Increased protein synthesis, decrease body fat - Also associated with negative side effects - Lose muscle mass after discontinuation  - Widespread use has led to testing of competitive athletes - Most users are not competitive athletes Adipose Tissue - Adipose tissue is primary area for triglyceride storage - Produces & releases hormones (Leptin) - Influences appetite & metabolism; ↑ insulin sensitivity; promotes fat oxidation - Rapid weight loss suppresses leptin; slow weight loss minimizes effect on leptin release - Obesity may ↓ leptin sensitivity & promote pro-inflammatory response - Ghrelin: secreted from stomach cells and promotes hunger