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Chapter 5 Hormonal Responses to Exercise

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1 Chapter 5 Hormonal Responses to Exercise
EXERCISE PHYSIOLOGY Theory and Application to Fitness and Performance, 6th edition Scott K. Powers & Edward T. Howley

2 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

3 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

4 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

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

6 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

7 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

8 Control of Hormone Secretion
Rate of insulin secretion from the pancreas is dependent on: Magnitude of input Stimulatory vs. inhibitory

9 Factors That Influence the Secretion of Hormones
Fig 5.1

10 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

11 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

12 Mechanism of Steroid Hormones
Fig 5.2

13 Cyclic AMP “Second Messenger” Mechanism
Fig 5.3

14 Other “Second Messenger” Systems
Fig 5.4

15 Hormones: Regulation and Action
Hormones are secreted from endocrine glands Hypothalamus and pituitary glands Thyroid and parathyroid glands Adrenal glands Pancreas Testes and ovaries

16 Hypothalamus Controls activity of the anterior and posterior pituitary glands Influenced by positive and negative input

17 Positive and Negative Input to the Hypothalamus
Fig 5.6

18 Anterior Pituitary Gland
Fig 5.5

19 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

20 Growth Hormone Fig 5.6

21 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

22 Change in the Plasma ADH Concentration During Exercise
Fig 5.7

23 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

24 Adrenal Medulla Secretes Epinephrine and Norepinephrine Increases
HR, glycogenolysis, lypolysis,

25 Adrenal Cortex Mineralcorticoids (aldosterone)
Maintain plasma Na+ and K+ Regulation of blood pressure

26 Change in Mineralcorticoids During Exercise
Fig 5.8

27 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

28 Control of Cortisol Secretion
Fig 5.9

29 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

30 Testes Release testosterone Anabolic steroid
Promotes tissue (muscle) building Performance enhancement Androgenic steroid Promotes masculine characteristics

31 Control of Testosterone Secretion
Fig 5.10

32 Estrogen Establish and maintain reproductive function
Levels vary throughout the menstrual cycle

33 Control of Estrogen Secretion
Fig 5.11

34 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

35 Control of Glycogenolysis
Fig 5.16

36 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 5.13 Fig 5.14

37 Glycogen Depletion During Exercise
Fig 5.13

38 Plasma Epinephrine Concentration During Exercise
Fig 5.14

39 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

40 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

41 Cortisol Stimulates FFA mobilization from adipose tissue
Mobilizes amino acids for gluconeogenesis Blocks entry of glucose into cells Fig 5.17

42 Role of Cortisol in the Maintenance of Blood Glucose
Fig 5.17

43 Plasma Cortisol During Exercise
At low intensity plasma cortisol decreases At high intensity plasma cortisol increases Fig 5.18

44 Changes in Plasma Cortisol During Exercise
Fig 5.18

45 Growth Hormone Important in the maintenance of plasma glucose
Decreases glucose uptake Increases FFA mobilization Enhances gluconeogenesis Fig 5.19

46 Growth Hormone in the Maintenance of Plasma Glucose
Fig 5.19

47 Growth Hormone During Exercise: Effect of Intensity
Fig 5.20

48 Growth Hormone During Exercise: Trained vs. Untrained
Fig 5.20

49 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

50 Role of Catecholamines in Substrate Mobilization
Fig 5.21

51 Epinephrine & Norepinephrine During Exercise
Increase linearly during exercise Favor the mobilization of FFA and maintenance of plasma glucose

52 Change in Plasma Catecholamines During Exercise
Fig 5.22

53 Epinephrine & Norepinephrine Following Training
Decreased plasma levels in response to exercise bout Parallels reduction in glucose mobilization

54 Plasma Catecholamines During Exercise Following Training
Fig 5.23

55 Effects of Insulin & Glucagon
Fig 5.24

56 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

57 Changes in Plasma Insulin During Exercise
Fig 5.25

58 Effect of Training on Plasma Insulin During Exercise
Fig 5.25

59 Effect of Training on Plasma Glucagon During Exercise
Fig 5.26

60 Effect of SNS on Substrate Mobilization
Fig 5.28

61 Hormonal Responses to Exercise
Fig 5.29a

62 Hormonal Responses to Exercise
Fig 5.29b

63 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

64 Effect of Lactic Acid on FFA Mobilization
Fig 5.30

65 Chapter 5 Hormonal Responses to Exercise

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