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Types of Hormones
• Amino acid derivatives– epinephrine, serotonin, melotonin
• Protein– insulin, parathyroid hormone, growth hormone
• Steroids– derived from cholesterol– sex hormones, mineralocorticoids,
prostaglandins
Hormone-receptor interaction
• Some hormones circulate to all tissues, but only act on some
• receptor must be present for effect to occur– eg thyroid stimulating hormone only exerts an
effect on the thyroid– conversely some hormones work on virtually
all tissues (insulin)
Blood Hormone Concentration
• the effect of a hormone related to concentration in blood (to a point)
• Concentration affected by 4 factors– rate of hormone secretion– rate of metabolism or excretion– transport proteins– plasma volume (affected by exercise)
Control of Hormone Secretion
• Rate of insulin secretion from the pancreas is dependent on:– Magnitude of input – Stimulatory vs. inhibitory
Mechanisms of Hormone Action
• alteration of membrane transport (insulin)
• stimulation of DNA synthesis (testosterone, estrogen)
• activation of “second messengers”– hormone doesn’t enter the cell
The Hypothalamus is the “Master Gland”
• the hypothalamus controls the pituitary in two ways– the hypothalamus can release “releasing
hormones”• releasing hormones act on anterior pituitary (TSH,
ACTH, GH)
– neurons originating in the hypothalamus act on posterior pituitary (ADH)
Growth Hormone
• uptake of amino acids and protein synthesis
• opposes insulin– reduces use of plasma glucose– increases gluconeogenesis– mobilizes FFA
Antidiuretic Hormone (ADH)
• causes resorbtion of H2O to maintain fluid
• stimulated by two factors– high plasma osmolality (sweating)– low plasma volume (loss of blood, exercise)
The Adrenal Glands
• Medulla– secretes epinephrine (E) and norepinephrine
(NE)
• Cortex– secretes mineralocorticoids, glucocorticoids
Response to Catecholamines: Role of Receptor Type
Receptor Type
Effect of E/NE
Membrane-bound enzyme
Intracellular mediator
Effects on Various Tissues
1 E=NE Adenylate cyclase cAMP Heart rate Glycogenolysis Lipolysis
2 E>>>NE Adenylate cyclase cAMP Bronchodilation Vasodilation
1 ENE Phospholipase C Ca++ Phosphodiesterase Vasoconstriction
2 ENE Adenylate cyclase cAMP Opposes action of 1 & 2 receptors
Aldosterone (Mineralocorticoid)
• regulates K+ and Na+ concentrations
• controls resorbtion in the kidney
• involved in thirst response
Cortisol• Actions
– promotes breakdown of tissue protein (inhibits protein synthesis)
– mobilizes FFA from adipose– stimulates gluconeogenesis– blocks entry of glucose into tissues (increases
fat utilization)
• Involved in adaptation response to stress (exercise)
Pancreas• Insulin
– aids in transport of glucose into cells– stimulated when blood sugar increases (storage
of glucose, amino acids and fat)– inhibited during exercise
• Glucagon– opposite effect of insulin– stimulated by low blood glucose– mobilizes glucose and fatty acids
Sex Hormones
• testosterone– elevated during short-term high intensity
exercise– levels typically lower in endurance trained
individuals
Estrogen
• promotes higher levels of fat metabolism ?
• chronic endurance training may suppress E2 (amenorrhea)
Muscle Glycogen Utilization
• glycogen metabolism controlled by epinephrine (cAMP) and intracellular Ca++ (calmodulin) from sarcoplasmic reticulum– epinephrine increases rapidly with intense
exercise– adrenergic blockade– glycogen depleted only in exercising muscles
• Ca++ faster than cAMP and more specific
Blood Glucose Homeostasis During Exercise
• mobilization of glucose from liver glycogen stores
• mobilization of plasma FFA from adipose tissue to spare plasma glucose
• synthesis of new glucose in the liver (gluconeogenesis) from AA, La, and glycerol
• blocking of glucose entry into cells to force the substitution of FFA as a fuel
Slow Acting Hormones
• Thyroxine– allows other hormones (eg epinephrine) to exert
effect
• Cortisol
• GH
Growth Hormone During Exercise
• Combine amino acids and glycerol to make glucose in the liver
• Breaks down triglycerides (fat) in the adipose tissue to make FFA available
• Blocks entry of glucose into the cell
• All of these go to maintain blood glucose
Fast Acting Hormones
• catecholamines (epinephrine and norepinephrine)
– N primarily neurotransmitter at synapse
– E primarily plasma hormone
• insulin
• glucagon
Catecholamines (adrenergic) During Exercise
• Break down glycogen in liver to free glucose available
• Break down triglycerides in the adipose tissue to make FFA available
• Block entry of glucose into the cell
Take home…
• Almost all of the hormonal responses will be attenuated with endurance training– Exception-growth hormone
Glucagon Response Reduced after Endurance Training Because…
• increased utilization of FFA as fuel substrate
• decreased reliance on plasma glucose
• therefore decreased reliance on liver glycogen
Glucose Uptake by Cells can Increase 7-25 Fold During
Exercise. How?
• increased blood flow to exercising tissues
• increased metabolism causes gradient (diabetics)
• increased # s of glucose transporter at membrane (diabetics)
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