Actions of thyroid hormones

  • By: Terri
  • Date: May 22, 2010
  • Time to read: 2 min.

Increase basal metabolic rate

  • Calorigenic action
    • action that increases BMR
  • Stimulates O2 consumption of almost all metabolically active tissues
    • except adult brain, testes, uterus, lymph nodes, spleen & anterior pituitary
  • T4 suppresses O2 consumption of the anterior pituitary
    • because it inhibits TSH secretion
  • Increase activity of Na/K ATPase in many tissues
  • Increase Mitochondrial protein synthesis
  • Hyperthyroidism
    • BMR 60-100% above normal
  • Hypothyroidism
    • BMR 20-40% below normal

Increase protein synthesis

  • Increase RNA translation
  • Increase transcription
  • Increase mitochondrion activity
  • Increase activity of enzyme

Carbohydrate metabolism

  • Increase absorption of glucose from GIT (similar to insulin)
  • Increase glucose uptake by the cells
    • accelerate glucose transport thru the cell membrane
  • Increase breakdown of glycogen to glucose
  • Accelerates gluconeogenesis

Lipid metabolism

  • Decreases lipid storage
    • mobilising it from adipose tissues
    • mobilised lipid is then converted to free FA & transported by blood
    • Free FA in blood increases
  • Decreases cholestreol, phospholipids & TG in plasma
    • Hyposecretion: increase cholesterol level – atherosclerosis
  • Increase deposition of lipids in liver –> fatty liver
  • Decrease plasma cholesterol by increasing excretion from liver cells into bile

Increase heat production in the body

  • accelerate cellular metabolic processes
  • thyroid hormone induced thermogenesis


  • accelerates growth of body
    • especially children
  • Growith & development of brain during detal life & first few years of postnatal life

Body weight

  • Decrease body weight & fat storage
    • Hypothyroidism: fat deposition


  • increase RBC production
    • Accelerates erythropoiesis
  • icrease dissociation of O2 from hemoglobin
    • by increasing 2,3-biphosphoglycerate (BPG)
    • For increased activity of tissues


  • Increase no. & affinity of B-adrenergic receptors in the heart
    • increase sensitivity to the inotropic (contractility) & chronotropic (rate) effects of cathecholamines


  • Increase rate & force of respiration
  • Increase metabolic rate, increased demand for O2 & formation of CO2
    • stimulates respiratory centers to increase rate & force of respiration


  • Increase appetite & food intake
  • Increase secretions & movements of GIT
  • Hypersecretion
    • Diarrhea
  • Hyposecretion
    • Constipation


  • Development & maintenance of normal function of CNS

Skeletal muscle

  • Essential for normal activity of skeletal muscle
  • Slight increase in hormone: muscle work more vigorously
  • Hypersecretion: muscle weakness
    • catabolism of proteins: thyrotoxic myopathy
  • Hypersecretion: fine muscular tremor
    • due to thyroxine-induced excess neuronal activity
  • Hyposecretion: sluggish muscle

Sexual function

  • Essential for normal sexual function
  • In man
    • hypersecretion: impotence
    • hyposecretion: loss of libido
  • In woman
    • hypersecretion: oligomenorrhea, amernorrhea
    • hyposecretion: menorrrhagia, polymenorrhea
      • some oligomenorrhea, amenorrhea

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