1. Hormonal Control During Exercise
Chapter 4
Hormonal Control During Exercise

2. Chapter 4 Overview Endocrine system
Hormones (types, receptors, actions)
Endocrine glands and their hormones
Hormonal regulation of metabolism during exercise
Hormonal regulation of fluid and electrolytes during exercise

3. The Endocrine System A communication system
Nervous system = electrical communication
Endocrine system = chemical communication
Slower responding, longer lasting than nervous system
Maintains homeostasis via hormones
Chemicals that control and regulate cell/organ activity
Act on target cells
Constantly monitors internal environment

4. The Endocrine System
Coordinates integration of physiological systems during rest and exercise
Maintains homeostasis during exercise
Controls substrate metabolism
Regulates fluid, electrolyte balance

5. Figure 4.1

6. Hormones: Steroid Hormones
Derived from cholesterol
Lipid soluble, diffuse through membranes
Secreted by four major glands
Adrenal cortex (cortisol, aldosterone)
Ovaries (estrogen, progesterone)
Testes (testosterone)
Placenta (estrogen, progesterone)

7. Hormones: Nonsteroid Hormones
Not lipid soluble, cannot cross membranes
Divided into two groups
Protein/peptide hormones
Most nonsteroid hormones
From pancreas, hypothalamus, pituitary gland,
Amino acid-derived hormones
Thyroid hormones (T3, T4)
Adrenal medulla hormones (epinephrine, norepinephrine)

8. Hormone Secretion Secreted in bursts (pulsatile)
Plasma concentrations fluctuate over minutes/hours
Concentrations also fluctuate over days/weeks
What triggers or regulates hormone bursts?
Secretion regulated by negative feedback
Hormone release causes change in body
High level of downstream change  secretion
Low level of downstream change  secretion
Example: home thermostat

9. Hormone Activity
Plasma concentration can be poor indicator of hormone activity
Cells change sensitivity to hormones
Number of receptors on cell surface can change
Downregulation:  number of receptors during high plasma concentration = desensitization
Upregulation:  number of receptors during high plasma concentration = sensitization

10. Hormone Receptors
Hormones limit scope of their effects by using hormone-specific receptors
No receptor on cell surface = no hormone effect
Hormone only affects tissues with specific receptor
Hormone exerts effects after binding with receptor
Typical cell has 2,000 to 10,000 receptors
Hormone binds to receptor: hormone–receptor complex

11. Steroid Hormone Actions
Lipid soluble (can cross cell membranes)
Steroid hormone receptors found inside cell, in cytoplasm or nucleus
Hormone–receptor complex enters nucleus
Binds to DNA, direct gene activation
Regulates mRNA synthesis, protein synthesis

12. Figure 4.2

13. Nonsteroid Hormone Actions
Not lipid soluble (cannot cross cell membrane)
Receptors on cell membrane  second messengers
Carry out hormone effects
Intensify strength of hormone signal
Common second messengers
Cyclic adenosine monophosphate (cAMP)
Cyclic guanine monophosphate (cGMP)
Inositol triphosphate (IP3), diacylglycerol (DAG)

14. Figure 4.3

15. Hormones: Prostaglandins
Third class of (pseudo)hormones
Derived from arachidonic acid
Act as local hormones, immediate area
Inflammatory response (swelling, vasodilation)
Sensitize nociceptor free nerve endings (pain)

16. Endocrine Glands and Their Hormones
Several endocrine glands in body; each may produce more than one hormone
Hormones regulate physiological variables during exercise

17. Hormonal Regulation of Metabolism During Exercise
Major endocrine glands responsible for metabolic regulation
Anterior pituitary gland
Thyroid gland
Adrenal gland
Pancreas
Hormones released by these glands affect metabolism of carbohydrate and fat during exercise

18. Endocrine Regulation of Metabolism: Anterior Pituitary Gland
Pituitary gland attached to inferior hypothalamus
Three lobes: anterior, intermediate, posterior
Secretes hormones in response to hypothalamic hormone factors
Releasing factors, inhibiting factors
Exercise  secretion of all anterior pituitary hormones

19. Endocrine Regulation of Metabolism: Anterior Pituitary Gland
Releases growth hormone (GH)
Potent anabolic hormone
Builds tissues, organs
Promotes muscle growth (hypertrophy)
Stimulates fat metabolism
GH release proportional to exercise intensity

20. Endocrine Regulation of Metabolism: Thyroid Gland
Secretes triiodothyronine (T3), thyroxine (T4)
T3 and T4 lead to increases in
Metabolic rate of all tissues
Protein synthesis
Number and size of mitochondria
Glucose uptake by cells
Rate of glycolysis, gluconeogenesis
FFA mobilization

21. Endocrine Regulation of Metabolism: Thyroid Gland
Anterior pituitary releases thyrotropin
Also called thyroid-stimulating hormone (TSH)
Travels to thyroid, stimulates T3 and T4
Exercise increases TSH release
Short term: T4  (delayed release)
Prolonged exercise: T4 constant, T3 

22. Endocrine Regulation of Metabolism: Adrenal Medulla
Releases catecholamines (fight or flight)
Epinephrine 80%, norepinephrine 20%
–  Exercise   sympathetic nervous system   epinephrine and norepinephrine
Catecholamine release increases
Heart rate, contractile force, blood pressure
– Glycogenolysis, FFA
Blood flow to skeletal muscle

23. Endocrine Regulation of Metabolism: Adrenal Cortex
Releases corticosteroids
Glucocorticoids
Also, mineralocorticoids, gonadocorticoids
Major glucocorticoid: cortisol
–  Gluconeogenesis
–  FFA mobilization, protein catabolism
Anti-inflammatory, anti-immune

24. Endocrine Regulation of Metabolism: Pancreas
Insulin: lowers blood glucose
Counters hyperglycemia, opposes glucagon
–  Glucose transport into cells
–  Synthesis of glycogen, protein, fat
– Inhibits gluconeogenesis
Glucagon: raises blood glucose
Counters hypoglycemia, opposes insulin
–  Glycogenolysis, gluconeogenesis

25. Regulation of Carbohydrate Metabolism During Exercise
Glucose must be available to tissues
Glycogenolysis (glycogen  glucose)
Gluconeogenesis (FFAs, protein  glucose)

26. Regulation of Carbohydrate Metabolism During Exercise
Adequate glucose during exercise requires
Glucose release by liver
Glucose uptake by muscles
Hormones that  circulating glucose
Glucagon
Epinephrine
Norepinephrine
Cortisol

27. Regulation of Carbohydrate Metabolism During Exercise
Circulating glucose during exercise also affected by
GH:  FFA mobilization,  cellular glucose uptake
T3, T4:  glucose catabolism and fat metabolism
Amount of glucose released from liver depends on exercise intensity, duration

28. Regulation of Carbohydrate Metabolism During Exercise
As exercise intensity increases
– Catecholamine release 
– Glycogenolysis rate  (liver, muscles)
Muscle glycogen used before liver glycogen
As exercise duration increases
More liver glycogen utilized
–  Muscle glucose uptake   liver glucose release
As glycogen stores , glucagon levels 

29. Figure 4.4

30. Regulation of Carbohydrate Metabolism During Exercise
Glucose mobilization only half the story
Insulin: enables glucose uptake in muscle
During exercise
Insulin concentrations 
Cellular insulin sensitivity 
More glucose uptake into cells, use less insulin

31. Figure 4.5

32. Regulation of Fat Metabolism During Exercise
FFA mobilization and fat metabolism critical to endurance exercise performance
Glycogen depleted, need fat energy substrates
In response, hormones accelerate fat breakdown (lipolysis)
Triglycerides  FFAs + glycerol
Fat stored as triglycerides in adipose tissue
Broken down into FFAs, transported to muscle
Rate of triglyceride breakdown into FFAs may determine rate of cellular fat metabolism

33. Regulation of Fat Metabolism During Exercise
Lipolysis stimulated by
(Decreased) insulin
Epinephrine
Norepinephrine
Cortisol GH
Stimulate lipolysis via lipase

34. Hormonal Regulation of Fluid and Electrolytes During Exercise
During exercise, plasma volume , causing
–  Hydrostatic pressure, tissue osmotic pressure
–  Plasma water content via sweating
–  Heart strain,  blood pressure
Hormones correct fluid imbalances
Posterior pituitary gland
Adrenal cortex
Kidneys

35. Hormonal Regulation of Fluid and Electrolytes: Posterior Pituitary
Secretes antidiuretic hormone (ADH), oxytocin
Produced in hypothalamus, travels to posterior pituitary
Secreted upon neural signal from hypothalamus
Only ADH involved with exercise
–  Water reabsorption at kidneys
Less water in urine, antidiuresis

36. Hormonal Regulation of Fluid and Electrolytes: Posterior Pituitary
Stimuli for ADH release
–  Plasma volume = hemoconcentration =  osmolality
–  Osmolality stimulates osmoreceptors in hypothalamus
ADH released, increasing water retention by kidneys
Minimizes water loss, severe dehydration

37. Figure 4.6

38. Hormonal Regulation of Fluid and Electrolytes: Adrenal Cortex
Secretes mineralocorticoids
Major mineralocorticoid: aldosterone
Aldosterone effects
–  Na+ retention by kidneys
–  Na+ retention   water retention via osmosis
–  Na+ retention   K+ excretion

39. Hormonal Regulation of Fluid and Electrolytes: Adrenal Cortex
Stimuli for aldosterone release
–  Plasma Na+
–  Blood volume, blood pressure
–  Plasma K+
Also indirectly stimulated by  blood volume,  blood pressure in kidneys

40. Hormonal Regulation of Fluid and Electrolytes: Kidneys
Target tissue for ADH, aldosterone
Secrete erythropoietin (EPO), renin
EPO
Low blood O2 in kidneys  EPO release
Stimulates red blood cell production
Critical for adaptation to training, altitude

41. Hormonal Regulation of Fluid and Electrolytes: Kidneys
Stimulus for renin (enzyme) release
 Blood volume,  blood pressure
Sympathetic nervous system impulses
Renin-angiotensin-aldosterone mechanism
Renin: converts angiotensinogen  angiotensin I
ACE: converts angiotensin I  angiotensin II
Angiotensin II stimulates aldosterone release

42. Figure 4.7

43. Figure 4.8

44. Figure 4.9

45. Hormonal Regulation of Fluid and Electrolytes: Osmolality
Measure of concentration of dissolved particles (proteins, ions, etc.) in body fluid compartments
Normal value: ~300 mOsm/kg
Osmolality and osmosis
If compartment osmolality , water drawn in
If compartment osmolality , water drawn out

46. Hormonal Regulation of Fluid and Electrolytes: Osmolality
Aldosterone and osmosis
Na+ retention   osmolality
–  Osmolality   water retention
Where Na+ moves, water follows
Osmotic water movement minimizes loss of plasma volume, maintains blood pressure

47. Hormonal Regulation of Fluid and Electrolytes: Osmolality
ADH, aldosterone effects persist for 12 to 48 h after exercise
Prolonged Na+ retention  abnormally high [Na+] after exercise
Water follows Na+
Prolonged rehydration effects