exercise phy

• Hypothalamus


  Part of the brain that controls the pituitary gland
• Pituitary gland


  Located at the base of the brain, attached to the hypothalamus. Has two lobes - anterior (adenohypophysis) and posterior (neurohypophysis)
• Anterior pituitary


  Hormone release is controlled by chemicals (releasing hormones or factors) from the hypothalamus. Secretes hormones like ACTH, FSH, LH, MSH, TSH, GH, Prolactin
• TSH


  Controls the rate of thyroid hormone formation and secretion from the thyroid gland
• ACTH


  Stimulates the production and secretion of cortisol in the adrenal cortex
• LH


  Stimulates the production of testosterone in the testes and estrogen in the ovaries
• GH


  Stimulates the release of insulin-like growth factors (IGFs) from the liver and other tissues
• IGF-1


  Produced in muscle due to muscle contraction, acts locally via autocrine and paracrine mechanisms and is a principal driver of muscle hypertrophy
• Growth hormone


  Secreted from the anterior pituitary gland, exerts profound effects on the growth of all tissues through the action of IGFs. Secretion is controlled by releasing hormones from the hypothalamus
• Factors that can influence GH secretion

  • Exercise (most potent stimulus)
  • Stress
  • Low plasma-glucose concentration
  • Sleep
• GH and IGFs


  Stimulate tissue uptake of amino acids, the synthesis of new protein, and long-bone growth
• GH


  Spares plasma glucose by opposing the action of insulin, increasing gluconeogenesis, and increasing mobilization of fatty acids
• GH increases with exercise to help maintain the plasma glucose concentration, and is also important after exercise to stimulate protein synthesis
• Posterior pituitary gland


  Receives hormones from neurons originating in the hypothalamus and stores and releases oxytocin and antidiuretic hormone (ADH)
• Oxytocin


  A powerful stimulator of smooth muscle, especially at the time of childbirth, and is also involved in the milk "let down" response
• Antidiuretic hormone (ADH)


  Reduces water loss from the body by favoring the reabsorption of water from the kidney tubules back into the capillaries
• Stimuli that cause increased ADH secretion

  • High plasma osmolality (low water concentration)
  • Low plasma volume (loss of blood or inadequate fluid replacement)
• During exercise, plasma volume decreases and osmolality increases, leading to increased ADH secretion to conserve water and maintain plasma volume
• Thyroid gland


  Stimulated by TSH to synthesize the iodine-containing hormones T3 and T4
• Thyroid hormones


  Central in establishing the overall metabolic rate. Act as permissive hormones allowing other hormones to exert their full effect
• The control of T3 and T4 secretion is an example of the negative feedback mechanism
• During exercise, the "free" thyroid hormone concentration increases due to changes in the binding characteristics of the transport proteins, and the hormones are taken up faster by tissues. To counter this, TSH secretion increases to stimulate more T3 and T4 secretion from the thyroid gland
• Resistance training has little effect on the pituitary (TSH)-thyroid (T3, T4) function
• Calcitonin


  Secreted by the thyroid gland, involved in the regulation of plasma calcium concentration
• Parathyroid hormone


  The primary hormone involved in plasma calcium regulation, stimulating bone to release calcium and the kidney to increase calcium absorption
• Parathyroid hormone increases during both intense and prolonged exercise, related to a lower calcium concentration and exercise-induced increases in plasma H+ and catecholamine concentrations
• Components of the adrenal gland

  • Adrenal medulla (secretes catecholamines)
  • Adrenal cortex (secretes steroid hormones)
• Catecholamines (epinephrine and norepinephrine)


  Secreted by the adrenal medulla, affect receptors in various systems and form the basis for the "fight or flight" response
• Steroid hormones secreted by the adrenal cortex

  • Mineralocorticoids (aldosterone)
  • Glucocorticoids (cortisol)
  • Sex steroids (androgens and estrogens)
• Aldosterone


  An important regulator of sodium reabsorption and potassium secretion in the kidney, involved in sodium/water balance and blood pressure regulation
• Regulation of aldosterone secretion

  1. Directly controlled by plasma potassium concentration

  2. Indirectly controlled by plasma volume, blood pressure, and sympathetic nerve activity (via renin-angiotensin system)
• Aldosterone


  Directly involved in Na+/H2O balance and, consequently, plasma volume and blood pressure
• Control over aldosterone secretion

  1. Release of aldosterone from the adrenal cortex is controlled directly by the plasma K+ concentration

  2. Decrease in plasma volume, fall in blood pressure at the kidney, or increase in sympathetic nerve activity to the kidney stimulates special cells in the kidney to secrete an enzyme called renin
• Increase in K+ concentration

  Increases aldosterone secretion, which stimulates the kidney's active transport mechanism to secrete K+ ions
• Renin secretion


  1. Decrease in plasma volume, fall in blood pressure at the kidney, or increase in sympathetic nerve activity to the kidney stimulates special cells in the kidney to secrete an enzyme called renin

  2. Renin enters the plasma and converts renin substrate (angiotensinogen) to angiotensin I

  3. Angiotensin I is converted to angiotensin II by angiotensin-converting enzyme (ACE) in the lungs
• Angiotensin II


  A powerful vasoconstrictor
• Individuals with hypertension may be prescribed an ACE inhibitor to lower blood pressure
• Angiotensin II


  Stimulates aldosterone release, which increases Na+ reabsorption
• The stimuli for aldosterone and ADH secretion are also the signals that stimulate thirst, a necessary ingredient to restore body fluid volume
• During light exercise, little or no change occurs in plasma renin activity or aldosterone