Hormonal Control During Exercise

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

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

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

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

Endocrine Regulation of Metabolism: Thyroid Gland Secretes triiodothyronine (T 3 ), thyroxine (T 4 ) T 3 and T 4 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

Endocrine Regulation of Metabolism: Thyroid Gland Anterior pituitary releases thyrotropin –Also called thyroid-stimulating hormone (TSH) –Travels to thyroid, stimulates T 3 and T 4 Exercise increases TSH release –Short term: T 4  (delayed release) –Prolonged exercise: T 4 constant, T 3 

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

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

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

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

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

Regulation of Carbohydrate Metabolism During Exercise Circulating glucose during exercise also affected by –GH:  FFA mobilization,  cellular glucose uptake –T 3, T 4 :  glucose catabolism and fat metabolism Amount of glucose released from liver depends on exercise intensity, duration

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 

Figure 4.4

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

Figure 4.5

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

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

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

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

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

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

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

Hormonal Regulation of Fluid and Electrolytes: Kidneys Kidneys –Target tissue for ADH, aldosterone –Secrete erythropoietin (EPO), renin EPO –Low blood O 2 in kidneys  EPO release –Stimulates red blood cell production –Critical for adaptation to training, altitude

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

Figure 4.8

Figure 4.9

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

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

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