Endocrine System and Exercise

1
Endocrine System and Exercise

• EXS 558
• Lecture 3
• September 14, 2005

2
Review Question 1

• By what two methods does the central nervous
  system regulate muscular force production?
• RATE CODING and RECRUITMENT

3
Review Question 2

• TRUE/FALSE With small homogenous muscle, first
  see ? rate coding of low threshold MUs, then see
  ? recruitment until reach 90 MVC, then ? rate
  coding to reach 100 MVC.

4
Review Question 3

• According to the size principle (Henneman et al.,
  1965) to following muscle fibers are recruited
  first during prolonged activity?
• a.) Type I
• b.) Type IIa
• c.) Type IIb
• d.) Type III

5
Review Question 4

• Why are slow-twitch muscle fibers selected first
  according to the size principle in exercises of
  long duration?
• smaller motor neurons
• Easier to stimulate an AP (action potential)
• lower threshold

6
Review Question 5

• Does the size principle apply to activities of
  shorter, higher intensity activities?
• According to Yamano et al. (2005) the size
  principle does not apply in thoroughbred horses

7
Review Question 6

• Which of the following is NOT TRUE regarding fast
  twitch (type II) motor neurons as compared to
  slow twitch (type I) motor neurons?
• a.) AP propagation is quicker
• b.) Myofiber CSA is larger
• c.) Increased calcium concentration
• d.) Have greater of myofibers associated with
  each motor neuron

8
Review Question 7

• What three neural adaptations occur as a result
  of resistance training?
• 1.) Synchronization and recruitment of additional
  motor units
• 2.) Coactivation of agonist and antagonist
  muscles
• 3.) Rate codingthe firing frequency of motor
  units

9
Review Question 8

• EMG activity increases OR decreases when
  activating both limbs as opposed to one limb
  singly.
• This is known as ________________

BILATERAL DEFICIT
10
Review Question 9

• TRUE/FALSE Early strength gains are a result of
  muscle hypertrophy.

11
Review Question 10

• What three neural adaptations occur as a result
  of endurance training?
• 1.) Increase in MU activation
• 2.) Rotation of activity among synergists and
  among MU of prime mover
• 3.) Training ? consistency of firing rates of
  motor neurons

12
Endocrine and Exocrine Functions

• Endocrine system composed of endocrine
  glandsductless glands that secrete hormones
  directly into the blood
• Exocrine glands secrete their products into ducts
  (e.g. sweat glands)
• Pancreas has both functions exocrinedigestive
  enzymes endocrineinsulin and glucagon

13
Basic Hormone Introduction

• Hormones chemical messengers that circulate in
  blood and interact with organs to help combat
  various stresses
• Primary role is maintain homeostasis
• Most hormones are synthesized in the endocrine
  glands
• Receptors are specific to hormones such that only
  the correct hormone will fit the correct
  receptoreach cell has 2,000 to 10,000 specific
  receptors

14
Hormone Regulation

• Negative Feedback secretion acts to inhibit
  further secretion (either direct or indirect)
• Self-limiting
• Positive Feedback secretion acts to stimulate
  further secretion
• Rare
• Ex oxytocin released by pituitary gland
  stimulats cervix dilation

15
Changes in Hormone Concentrations

• Increases affected by physiological
  mechanisms
• 1.) Exercise
• 2.) Physical Stress
• 3.) Psychological Stress
• 4.) Fluid volume shifts
• 5.) Venous pooling of blood
• ? potential for receptor interaction
• Receptors are specific to hormones such that only
  the correct hormone will fit the correct
  receptoreach cell has 2,000 to 10,000 specific
  receptors

16
Lock-and-Key Theory

• Hormone-receptor interaction
• Hormone key
• Receptor lock
• Cross-reactivity more than one hormone can bind
  with a receptor
• This changes subsequent biological rxns
• Signal sent to nucleus for inhibition or
  facilitation of protein synthesis

17
Alteration of Receptors
Down-regulationDecrease in number of cell
receptors less hormone can bind to the cell and
higher concentrations of the hormone remain in
the blood plasma
Up-regulationIncrease in number of cell
receptors more hormone can bind to the cell and
lower concentrations of the hormone remain in the
blood plasma
18
Types of Hormones

• 1.) Steroids
• Ex testosterone, cortisol
• 2.) Peptides
• Ex HGH (human growth hormone), insulin

19
Steroid Hormones
w Lipid soluble
w Diffuse easily through cell membranes
receptors located within cell
w Chemical structure is derived from or is
similar to cholesterol
w Secreted by adrenal cortex (e.g., cortisol),
ovaries (e.g., estrogen), testes (e.g.,
testosterone), placenta (e.g., estrogen)
20
Steroid Hormone (cont)
21
Peptide Hormones
w Lipid soluble
w Diffuse easily through cell membranes
receptors located within cell
w Chemical structure is derived from or is
similar to cholesterol
w Secreted by adrenal cortex (e.g., cortisol),
ovaries (e.g., estrogen), testes (e.g.,
testosterone), placenta (e.g., estrogen)
22
Peptide Hormone (cont)
23
Nature of Hormones
w Hormones are classified into steroidal types
(lipid soluble and formed from cholesterol) or
nonsteroidal types (nonlipid soluble and formed
from amino acids, peptides, or proteins).
w Hormones are secreted in the blood and travel
to sites where they exert an effect on only those
target cells that have receptors specific to that
hormone.
24
w Nonsteroid hormones bind to receptors on the
cell membrane, which triggers a second messenger
within the cell, which in turn triggers numerous
cellular processes.
w A negative feedback system regulates the
release of most hormones.
w The number of receptors on a cell can change
the cell's sensitivity to hormones. Up-regulation
is the increase of receptors and down-regulation
is the decrease in receptors.
25
Testosterone (steroid hormone)

• Androgen ? masculinizing effects
• Anabolic ? maintains and aids in growth of muscle
  and bone tissue
• Produced in the testes under stimulus from
  luteinizing hormone (LH)

26
Acute Exercise Response
27
Fluid Regulatory Hormones

• Job maintain electrolyte balance
• Important in prolonged exercise
• Hormonal action effects both renal and
  circulatory system to prevent dehydration

28
Fluid Regulatory Hormones (cont)
AldosteroneReleased by the adrenal cortex in
response to decreased blood pressure promotes
sodium reabsorption in kidneys and increases
plasma volume.
Anitdiuretic hormone (ADH)Released by the
posterior pituitary in response to increased
blood osmolarity promotes water conservation by
increasing plasma volume.
29
How ADH conserves body water
ADH antidiuretic hormone (arginine vasopressin)
30
RENIN-ANGIOTENSIN MECHANISM
31
(No Transcript)
32
Fluid Regulation
Following the initial drop, plasma volume remains
relatively constant throughout exercise due to
1. The actions of aldosterone and ADH,
2. Water returning from the exercising muscles to
the blood, and
3. The increase in amount of water produced by
metabolic oxidation within muscles.
33
Hormones and Fluid Balance
w Aldosterone and ADH are the two primary
hormones involved in regulating fluid balance.
w When plasma volume or blood pressure decrease,
the kidneys produce renin that eventually
converts to angiotensin II.
34
Hormones and Fluid Balance
w Aldosterone promotes sodium reabsorption in the
kidneys, which in turn causes water retention,
thus increasing the plasma volume.
w ADH is released in response to increased plasma
osmolarity and acts on the kidneys to promote
water conservation.
w Plasma volume increases, which results in
dilution of the plasma solutes and blood
osmolarity decreases.