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8/19/2019 Respostas hormonais
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2010-2111
Fisiologia do Exercício
Hormonal Responses
to Exercise
EXERCISE PHYSIOLOGY
Theory and Application to Fitness and
Performance,
6th edition
Scott K. Powers & Edward T. Howley
2010-2111
Fisiologia do Exercício
Neuroendocrinology
• Endocrine glands release hormones directly
into the blood• Hormones alter the activity of tissues that
possess receptors to which the hormone can
bind
• The plasma hormone concentration
determines the magnitude of the effect at the
tissue level
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Blood Hormone ConcentrationDetermined by:
• Rate of secretion of hormone from endocrine
gland
• Rate of metabolism or excretion of hormone
• Quantity of transport protein
• Changes in plasma volume
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Fisiologia do Exercício
Control of Hormone Secretion
• Rate of insulin secretion from the pancreas is
dependent on:
– Magnitude of input
– Stimulatory vs. inhibitory
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Factors That Influence the Secretion of
Hormones
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Hormone-Receptor Interactions
• Trigger events at the cell
•
Magnitude of effect dependent on: – Concentration of the hormone
– Number of receptors on the cell
– Affinity of the receptor for the hormone
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Hormone-Receptor Interactions
• Hormones bring about effects by:
– Altering membrane transport
– Stimulating DNA to increase protein synthesis
– Activating second messengers
• Cyclic AMP
• Ca++
• Inositol triphosphate
• Diacylglycerol
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Mechanism of Steroid Hormones
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Cyclic AMP “Second Messenger”Mechanism
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Other “Second Messenger”
Systems
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Hormones:Regulation and Action
• Hormones are secreted from endocrine glands
– Hypothalamus and pituitary glands
– Thyroid and parathyroid glands
– Adrenal glands
– Pancreas – Testes and ovaries
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Hypothalamus
• Controls activity of the anterior and posterior
pituitary glands
• Influenced by positive and negative input
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Positive and Negative Inputto the Hypothalamus
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Anterior Pituitary Gland
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Growth Hormone• Secreted from the anterior pituitary gland
• Essential for normal growth
– Stimulates protein synthesis and long bonegrowth
• Increases during exercise
–
Mobilizes fatty acids from adipose tissue – Aids in the maintenance of blood glucose
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Growth
Hormone
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Thyroid Gland• Triiodothyronine (T3) and thyroxine (T4)
– Important in maintaining metabolic rate
and allowing full effect of other
hormones
• Calcitonin
– Regulation of plasma Ca++
• Parathyroid Hormone
– Also involved in plasma Ca++ regulation
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Adrenal Medulla
•Secretes Epinephrine and Norepinephrine
•Increases
– HR, glycogenolysis, lypolysis,
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Adrenal Cortex
• Mineralcorticoids (aldosterone)
– Maintain plasma Na+ and K+
– Regulation of blood pressure
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Change in Mineralcorticoids During
Exercise
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Adrenal Cortex• Glucocorticoids (Cortisol)
– Stimulated by exercise and long-term
fasting
– Promotes the use of free fatty acids as fuel
– Stimulates glucose synthesis
– Promotes protein breakdown for
gluconeogenesis and tissue repair
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Control of
Cortisol
Secretion
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Pancreas• Secretes digestive enzymes and
bicarbonate into small intestine
• Releases
– Insulin - Promotes the storage of glucose,
amino acids, and fats
– Glucagon - Promotes the mobilization of fatty
acids and glucose
– Somatostatin - Controls rate of entry of
nutrients into the circulation
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Testes
• Release testosterone
–
Anabolic steroid•Promotes tissue (muscle) building
•Performance enhancement
– Androgenic steroid
•Promotes masculine characteristics
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Control ofTestosterone
Secretion
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Estrogen
• Establish and maintain reproductive function
• Levels vary throughout the menstrual cycle
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Control ofEstrogen
Secretion
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Muscle Glycogen Utilization
• Breakdown of muscle glycogen is under dual
control
– Epinephrine-cyclic AMP
– Ca2+-calmodulin
• Delivery of glucose parallels activation of muscle
contraction
• Glycogenolysis – breakdown of glycogen
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Control of Glycogenolysis
Glycogenolysis
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Muscle Glycogen Utilization
• Glycogenolysis is related to exercise intensity
– High-intensity of exercise results in greater and
more rapid glycogen depletion
• Plasma epinephrine is a powerful simulator of
glycogenolysis
– High-intensity of exercise results in greater
increases in plasma epinephrine
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Glycogen Depletion During Exercise
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Plasma Epinephrine Concentration
During Exercise
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Cortisol
• Stimulates FFA mobilization from adipose
tissue
• Mobilizes amino acids for gluconeogenesis
• Blocks entry of glucose into cells
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Role of Cortisol in the Maintenance of Blood
Glucose
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Plasma Cortisol During Exercise
• At low intensity
– plasma cortisol decreases
• At high intensity
– plasma cortisol increases
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Changes in Plasma Cortisol During
Exercise
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Growth Hormone During Exercise:
Effect of Intensity
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Growth Hormone During Exercise:
Trained vs. Untrained
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Blood Glucose Homeostasis During
Exercise• Fast-acting hormones
– Norepinephrine and epinephrine
– Insulin and glucagon
• Maintain plasma glucose
– Increasing liver glucose mobilization
– Increased levels of plasma FFA
– Decreasing glucose uptake
– Increasing gluconeogenesis
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Role of Catecholamines in Substrate
Mobilization
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Epinephrine & Norepinephrine DuringExercise
• Increase linearly during exercise
• Favor the mobilization of FFA and
maintenance of plasma glucose
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Change in Plasma Catecholamines During
Exercise
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Epinephrine & Norepinephrine Following
Training
• Decreased plasma levels in response to
exercise bout
• Parallels reduction in glucose mobilization
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Plasma Catecholamines During Exercise
Following Training
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Effects of Insulin & Glucagon
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Insulin During Exercise
• Plasma insulin decreases during exercise
– Prevents rapid uptake of plasma glucose
– Favors mobilization of liver glucose and lipid
FFA
• Trained subjects during exercise
– More rapid decrease in plasma insulin
– Increase in plasma glucagon
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Changes in Plasma Insulin During
Exercise
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Effect of Training on Plasma Insulin
During Exercise
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Hormonal Responses to Exercise
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Hormonal Responses to Exercise
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Free Fatty Acid Mobilization DuringHeavy Exercise
• FFA mobilization decreases during heavy exercise
– This occurs in spite of persisting hormonal stimulation for
FFA mobilization
• May be due to high levels of lactic acid
– Promotes resynthesis of triglycerides
– Inadequate blood flow to adipose tissue
– Insufficient transporter for FFA in plasma
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Effect of Lactic Acid on FFA
Mobilization
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