Endocrine System and Exercise EXS 558 Lecture #3 September 14, 2005

Endocrine Endocrine System and System and

ExerciseExercise

EXS 558EXS 558

Lecture #3Lecture #3

September 14, 2005September 14, 2005

Review Question #1Review Question #1

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


TRUE/FALSE: With TRUE/FALSE: With small small homogenous musclehomogenous muscle, first see , first see ↑ ↑ rate rate coding of low threshold MU’s, then coding of low threshold MU’s, then see see ↑ ↑ recruitment until reach 90% recruitment until reach 90% MVC, then MVC, then ↑↑ rate coding to reach rate coding to reach 100% MVC.100% MVC.

Review Question #3Review Question #3According to the size principle According to the size principle (Henneman et al., 1965) to following (Henneman et al., 1965) to following muscle fibers are recruited first muscle fibers are recruited first during prolonged activity?during prolonged activity?a.) Type Ia.) Type Ib.) Type IIab.) Type IIac.) Type IIbc.) Type IIbd.) Type IIId.) Type III

Review Question #4Review Question #4Why are slow-twitch muscle fibers selected Why are slow-twitch muscle fibers selected first according to the size principle in first according to the size principle in exercises of long duration?exercises of long duration?

smaller motor neuronssmaller motor neurons– Easier to stimulate an AP (action potential)Easier to stimulate an AP (action potential)

lower thresholdlower threshold


Does the size principle apply to Does the size principle apply to activities of shorter, higher intensity activities of shorter, higher intensity activities?activities?

According to Yamano et al. (2005) the size According to Yamano et al. (2005) the size principle does not apply in thoroughbred principle does not apply in thoroughbred horseshorses


Which of the following is NOT TRUE Which of the following is NOT TRUE regarding fast twitch (type II) motor regarding fast twitch (type II) motor neurons as compared to slow twitch neurons as compared to slow twitch (type I) motor neurons?(type I) motor neurons?a.) AP propagation is quickera.) AP propagation is quicker

b.) Myofiber CSA is largerb.) Myofiber CSA is larger

c.) Increased calcium concentrationc.) Increased calcium concentration

d.) Have greater # of myofibers d.) Have greater # of myofibers associated with each motor neuronassociated with each motor neuron


What three neural adaptations occur What three neural adaptations occur as a result of resistance training?as a result of resistance training?1.) Synchronization and recruitment of additional motor units2.) Coactivation of agonist and antagonist muscles3.) Rate coding—the firing frequency of motor units


EMG activity EMG activity increasesincreases OR OR decreasesdecreases when activating both when activating both limbs as opposed to one limb singly.limbs as opposed to one limb singly.

This is known as ________________This is known as ________________BILATERAL DEFICIT


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


What three neural adaptations occur What three neural adaptations occur as a result of endurance training?as a result of endurance training?1.) Increase in MU activation1.) Increase in MU activation

2.) 2.) Rotation of activity among synergists and Rotation of activity among synergists and among MU of prime moveramong MU of prime mover

3.) Training ↑ consistency of firing rates of motor 3.) Training ↑ consistency of firing rates of motor neuronsneurons

Endocrine and Exocrine FunctionsEndocrine and Exocrine FunctionsEndocrine system composed of endocrine glands—ductless glands that secrete hormones directly into the blood

Exocrine glands secrete their products into ducts (e.g. sweat glands)

Pancreas has both functions: exocrine—digestive enzymes; endocrine—insulin and glucagon

Basic Hormone IntroductionBasic Hormone IntroductionHormones: chemical messengers that circulate in Hormones: chemical messengers that circulate in blood and interact with organs to help combat blood and interact with organs to help combat various stressesvarious stresses– Primary role is maintain homeostasisPrimary role is maintain homeostasis

Most hormones are synthesized in the endocrine Most hormones are synthesized in the endocrine glandsglands

Receptors are specific to hormones such that only the correct hormone will “fit” the correct receptor—each cell has 2,000 to 10,000 specific receptors

Hormone RegulationHormone Regulation

Negative FeedbackNegative Feedback: secretion acts to : secretion acts to inhibit further secretion inhibit further secretion (either direct or (either direct or indirect)indirect)

Self-limitingSelf-limiting

Positive FeedbackPositive Feedback: secretion acts to : secretion acts to stimulate further secretionstimulate further secretion

RareRare

Ex: oxytocin released by pituitary gland stimulats Ex: oxytocin released by pituitary gland stimulats cervix dilationcervix dilation

Changes in Hormone ConcentrationsChanges in Hormone Concentrations

Increases [ ] affected by physiological mechanismsIncreases [ ] affected by physiological mechanisms1.) Exercise1.) Exercise2.) Physical Stress2.) Physical Stress3.) Psychological Stress3.) Psychological Stress4.) Fluid volume shifts4.) Fluid volume shifts5.) Venous pooling of blood5.) Venous pooling of blood

↑ ↑ potential for receptor interactionpotential for receptor interactionReceptors are specific to hormones such that only the correct hormone will “fit” the correct receptor—each cell has 2,000 to 10,000 specific receptors

Lock-and-Key TheoryLock-and-Key Theory

Hormone-receptor interactionHormone-receptor interaction

Hormone = keyHormone = key

Receptor = lockReceptor = lock

Cross-reactivityCross-reactivity: more than one : more than one hormone can bind with a receptorhormone can bind with a receptor

This changes subsequent biological rxnsThis changes subsequent biological rxns

Signal sent to nucleus for inhibition Signal sent to nucleus for inhibition or facilitation of protein synthesisor facilitation of protein synthesis

Alteration of ReceptorsAlteration of ReceptorsDown-regulation—Decrease in number of cell receptors; less hormone can bind to the cell and higher concentrations of the hormone remain in the blood plasma

Up-regulation—Increase in number of cell receptors; more hormone can bind to the cell and lower concentrations of the hormone remain in the blood plasma

Types of HormonesTypes of Hormones

1.) Steroids1.) SteroidsEx: testosterone, cortisolEx: testosterone, cortisol

2.) Peptides2.) PeptidesEx: HGH (human growth hormone), insulinEx: HGH (human growth hormone), insulin

Steroid HormonesSteroid HormonesLipid soluble

Diffuse easily through cell membranes; receptors located within cell

Secreted by adrenal cortex (e.g., cortisol), ovaries (e.g., estrogen), testes (e.g., testosterone), placenta (e.g., estrogen)

Chemical structure is derived from or is similar to cholesterol

Steroid Hormone (con’t)Steroid Hormone (con’t)

Peptide HormonesPeptide HormonesLipid soluble

Diffuse easily through cell membranes; receptors located within cell

Secreted by adrenal cortex (e.g., cortisol), ovaries (e.g., estrogen), testes (e.g., testosterone), placenta (e.g., estrogen)

Chemical structure is derived from or is similar to cholesterol

Peptide Hormone (con’t)Peptide Hormone (con’t)

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).

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.

Nature of Hormones

(continued)

Steroid hormones pass through cell membranes and bind to receptors within the cell. They synthesize protein via a process called direct gene activation.

Nonsteroid hormones bind to receptors on the cell membrane, which triggers a second messenger within the cell, which in turn triggers numerous cellular processes.

A negative feedback system regulates the release of most hormones.

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.

Testosterone Testosterone (steroid hormone)(steroid hormone)

Androgen Androgen masculinizing effectsmasculinizing effects

Anabolic Anabolic maintains and aids in growth of maintains and aids in growth of muscle and bone tissuemuscle and bone tissue

Produced in the testes under stimulus from Produced in the testes under stimulus from luteinizing hormone (LH)luteinizing hormone (LH)

Acute Exercise ResponseAcute Exercise Response

Fluid Regulatory HormonesFluid Regulatory Hormones

Job: maintain electrolyte balanceJob: maintain electrolyte balanceImportant in prolonged exerciseImportant in prolonged exercise

Hormonal action effects both renal Hormonal action effects both renal and circulatory system to prevent and circulatory system to prevent dehydrationdehydration

Fluid Regulatory Hormones (con’t)Fluid Regulatory Hormones (con’t)Aldosterone—Released 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.

How ADH conserves body waterHow ADH conserves body water

ADH = antidiuretic hormone (arginine vasopressin)

RENIN-ANGIOTENSIN MECHANISM

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.

Fluid RegulationFluid Regulation

Aldosterone and ADH are the two primary hormones involved in regulating fluid balance.

When plasma volume or blood pressure decrease, the kidneys produce renin that eventually converts to angiotensin II.

Hormones and Fluid Balance

(continued)

Angiotensin II increases peripheral arterial resistance, which increases blood pressure and triggers the release of aldosterone.

Aldosterone promotes sodium reabsorption in the kidneys, which in turn causes water retention, thus increasing the plasma volume.

ADH is released in response to increased plasma osmolarity and acts on the kidneys to promote water conservation.

Hormones and Fluid Balance

Plasma volume increases, which results in dilution of the plasma solutes and blood osmolarity decreases.

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Endocrine System and Exercise EXS 558 Lecture #3 September 14, 2005