chapter 5 hormonal responses to exercise

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Chapter 5Hormonal Responses

to Exercise

EXERCISE PHYSIOLOGY

Theory and Application to Fitness and Performance, 6th edition

Scott K. Powers & Edward T. Howley


Objectives

• Describe the hormone-receptor interaction• Identify four factors that influence the

contraction of a hormone in the blood• Describe how steroid hormones act on cells• Describe “second messenger” hormone action• Describe the role of hypothalamus-releasing

factors in the control of hormone secretion from the anterior and posterior pituitary


Objectives

• Identify the site of release, stimulus for release, and the predominate action of the following hormones: epinephrine, norepinephrine, glucagon, insulin, cortisol, aldosterone, thyroxine, growth hormone, estrogen, and testosterone

• Discuss the use of anabolic steroid and growth hormone on muscle growth and their potential side effects


Objectives

• Contrast the role of plasma catecholamines with intracellular factors in the mobilization of muscle glycogen during exercise

• Graphically describe the changes in the following hormones during graded and prolonged exercise and discuss how those changes influence the four mechanisms used to maintain the blood glucose concentration: insulin, glucagon, cortisol, growth hormone, epinephrine, and norepinephrine


Objectives

• Describe the effect of changing hormone and substrate levels in the blood on the mobilization of free fatty acids from adipose tissue


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


Blood Hormone Concentration

Determined by:• Rate of secretion of hormone from endocrine

gland• Rate of metabolism or excretion of hormone• Quantity of transport protein• Changes in plasma volume


Control of Hormone Secretion

• Rate of insulin secretion from the pancreas is dependent on:– Magnitude of input– Stimulatory vs. inhibitory


Factors That Influence the Secretion of Hormones

Fig 5.1


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


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


Fig 5.2

Mechanism of Steroid

Hormones


Fig 5.3

Cyclic AMP“Second

Messenger” Mechanism


Fig 5.4

Other “Second

Messenger” Systems


Hormones: Regulation and Action

• Hormones are secreted from endocrine glands– Hypothalamus and pituitary glands– Thyroid and parathyroid glands– Adrenal glands– Pancreas– Testes and ovaries


Hypothalamus

• Controls activity of the anterior and posterior pituitary glands

• Influenced by positive and negative input


Fig 5.6

Positive and Negative Input

to the Hypothalamus


Anterior Pituitary Gland

Fig 5.5


Growth Hormone

• Secreted from the anterior pituitary gland• Essential for normal growth

– Stimulates protein synthesis and long bone growth

• Increases during exercise– Mobilizes fatty acids from adipose tissue– Aids in the maintenance of blood glucose


Growth Hormone

Fig 5.6


Posterior Pituitary Gland

• Secretes antidiuretic hormone (ADH) or vasopressin

• Reduces water loss from the body to maintain plasma volume

• Stimulated by:– High plasma osmolality and low plasma

volume due to sweating– Exercise


Change in the Plasma ADH Concentration During Exercise

Fig 5.7


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


Adrenal Medulla

• Secretes Epinephrine and Norepinephrine

• Increases

–HR, glycogenolysis, lypolysis,


Adrenal Cortex

• Mineralcorticoids (aldosterone)

– Maintain plasma Na+ and K+

– Regulation of blood pressure


Change in Mineralcorticoids During Exercise

Fig 5.8


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


Control of Cortisol

Secretion

Fig 5.9


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


Testes

• Release testosterone

– Anabolic steroid

• Promotes tissue (muscle) building

• Performance enhancement

– Androgenic steroid

• Promotes masculine characteristics


Control of Testosterone

Secretion

Fig 5.10


Estrogen

• Establish and maintain reproductive function

• Levels vary throughout the menstrual cycle


Control of Estrogen Secretion

Fig 5.11


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

Fig 5.16


Control of Glycogenolysis

Fig 5.16

Glycogenolysis


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 Fig 5.14

Fig 5.13


Glycogen Depletion During Exercise

Fig 5.13


Plasma Epinephrine Concentration During Exercise

Fig 5.14


Maintenance of Plasma Glucose During Exercise

• Mobilization of glucose from liver glycogen stores

• Mobilization of FFA from adipose tissue – Spares blood glucose

• Gluconeogenesis from amino acids, lactic acid, and glycerol

• Blocking the entry of glucose into cells– Forces use of FFA as a fuel


Blood Glucose Homeostasis During Exercise

• Permissive and slow-acting hormones

– Thyroxine

– Cortisol

– Growth hormone

• Act in a permissive manner to support actions of other hormones


Cortisol

• Stimulates FFA mobilization from adipose tissue

• Mobilizes amino acids for gluconeogenesis

• Blocks entry of glucose into cells

Fig 5.17


Role of Cortisol in the Maintenance of Blood

Glucose

Fig 5.17


Plasma Cortisol During Exercise

• At low intensity – plasma cortisol decreases

• At high intensity – plasma cortisol increases

Fig 5.18


Changes in Plasma Cortisol During Exercise

Fig 5.18


Growth Hormone

• Important in the maintenance of plasma glucose– Decreases glucose uptake– Increases FFA mobilization– Enhances gluconeogenesis

Fig 5.19


Growth Hormone in the Maintenance of Plasma Glucose

Fig 5.19


Growth Hormone During Exercise:Effect of Intensity

Fig 5.20


Growth Hormone During Exercise:Trained vs. Untrained

Fig 5.20


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

Fig 5.21


Role of Catecholamines in Substrate Mobilization

Fig 5.21


Epinephrine & Norepinephrine During Exercise

• Increase linearly during exercise• Favor the mobilization of FFA and

maintenance of plasma glucose


Change in Plasma Catecholamines During Exercise

Fig 5.22


Epinephrine & Norepinephrine Following Training

• Decreased plasma levels in response to exercise bout

• Parallels reduction in glucose mobilization


Plasma Catecholamines During Exercise Following

Training

Fig 5.23


Effects of Insulin & Glucagon

Fig 5.24


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


Changes in Plasma Insulin During Exercise

Fig 5.25


Effect of Training on Plasma Insulin During Exercise

Fig 5.25


Effect of Training on Plasma Glucagon During Exercise

Fig 5.26


Effect of SNS on Substrate Mobilization

Fig 5.28


Hormonal Responses to Exercise

Fig 5.29a


Hormonal Responses to Exercise

Fig 5.29b


Free Fatty Acid Mobilization During Heavy 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


Effect of Lactic Acid on FFA Mobilization

Fig 5.30


Chapter 5Hormonal Responses

to Exercise

chapter 5 hormonal responses to exercise

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