Download Hormones

Hormonal Control
During Exercise
CHAPTER 4 Overview
• Endocrine system
• Hormones (types, receptors, actions)
• Endocrine glands and their hormones
• Hormonal regulation of metabolism during exercise
• Hormonal regulation of fluid and electrolytes during
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
– Chemicals that control and regulate cell/organ
activity
– Act on target cells
• Constantly monitors internal environment
The Endocrine System
• Coordinates integration of physiological
systems during rest and exercise
• Maintains homeostasis during exercise
– Controls substrate metabolism
– Regulates fluid, electrolyte balance
Figure 4.1
Hormones: Steroid Hormones
• Derived from cholesterol
• Lipid soluble, diffuse through membranes
• Secreted by four major glands
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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
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Hormone release causes change in body
High level of downstream change  secretion
Low level of downstream change  secretion
Example: home thermostat
Hormone Activity
• Plasma concentration can be poor indicator
of hormone activity
– 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
Hormone Receptors
• Hormones limit scope of their effects by
using 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
Steroid Hormone Actions
• Lipid soluble (can cross cell membranes)
• Steroid hormone receptors found inside
cell, in cytoplasm or nucleus
• Hormone–receptor complex enters nucleus
– Binds to DNA, direct gene activation
– Regulates mRNA synthesis, protein synthesis
Figure 4.2
Nonsteroid Hormone Actions
• Not lipid soluble (cannot cross cell
membrane)
• Receptors on cell membrane  second
messengers
– Carry out hormone effects
– Intensify strength of hormone signal
• Common second messengers
– Cyclic adenosine monophosphate (cAMP)
– Cyclic guanine monophosphate (cGMP)
– Inositol triphosphate (IP3), diacylglycerol (DAG)
Figure 4.3
Hormones: 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)
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
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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)
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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
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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
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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
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(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
Figure 4.6
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 4.7
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