respostas hormonais

8/19/2019 Respostas hormonais

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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


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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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

respostas hormonais

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