Download Hormonal Regulation of Fluid and Electrolytes: Adrenal Cortex

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 (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
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 
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
– T3, T4:  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 O2 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