Pituitary Hormones

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Growth Hormone (Somatotropin)

  • Naturally occurring protein hormone
  • Regulates body growth
  • Effects of GH
    • Direct
      • Reduced glucose transport and metabolism
      • Increased lipolysis
      • Increased amino acid transport
      • Increased protein synthesis
      • Increased IGF-I production
      • Increased fibroblast differentiation
    • Indirect
      • Promotion of growth and endocrine effects
      • Reduction in insulin receptors in liver
      • Localized decrease in adipose tissue
        • free fatty acids released
      • Increases in both transcription and translation
      • Chondrocyte, osteoblast, and adipocyte formation
    • Muscle Growth
      • increased rates of muscle protein synthesis
      • decreased protein degradation
      • increased RNA and DNA
        • often accompanying increased protein accretion
      • increased DNA is likely a result of increased satellite cell activity
    • Bone Growth
      • mediated through IGF-I
        • IGF-I
          • increases chrondrocyte proliferation
          • increases osteoblast activity
        • GH leads to increased bone length prior to epiphyseal closure
        • GH increases periosteal growth contributing to increased bone mass
  • Regulation of Growth Hormone Secretion
    • Events increasing rate of release
      • Starvation
        • Hypoglycemia
          • Acute hypoglycemia: potent stimulator of GH release
        • Low FA in blood
        • Severe chronic protein deprivation
          • high circulating GH levels
      • Stress
        • Excitement
        • Trauma
      • Exercise
      • Amino Acid Supplementation
        • Arginine, Orthanine
      • PreREM Sleep
    • Hypothalamus
      • Growth hormone releasing hormone
      • Somatostatin / growth hormone inhibitory hormone
    • Neurotransmitters increasing GH release
      • Catecholamines
      • Dopamine
      • Serotonin
  • Metabolic effects
    • Increased lipolysis
    • Increased protein synthesis
      • GH effect on muscle is mediated through IGF-I and binding sites for IGF-I
    • Decreased glucose use
    • Interacts with receptors on cell membrane
      • Liver, kidney, muscle
      • Causes release of IGF-I into circulation
        • inturn activates target tissue
        • various binding proteins are involved in transporting IGF-I to target tissue
    • Growth hormone is species specific
  • IGF-I
    • can stimulate proliferation and differentiation of myoblasts
    • increases uptake of glucose and amino acids into muscle
    • negative feedback on pituitary
    • increases release of somatostatin

TSH

FSH, LH

  • FSH: Follical Stimulating Hormone
    • Women: FSH (assisted by LH) acts on follicle in Ovary, stimulating release of estrogens.
      Men: FSH acts on spermatogonia stimulating (with aid of testosterone) production of sperm.
  • LH: Luteinizing Hormone (or Lutropin)
    • Women
      • surge of LH triggers completion of meiosis I of egg and its release (ovulation) in middle of cycle
      • LH then stimulates empty follicle to develop into corpus luteum, which secretes progesterone during the latter half of the menstrual cycle.
    • Men: LH controls development of interstitial tissue in the testis and the secretion of testosterone
  • Also see

Prolactin

  • Regulates milk production

Oxytocin

  • Milk release

ACTH

  • Stimulates adrenal production of Cortisol

ADH

  • Fluid balance


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