Actions of T3 and T4

The actions of T3 and T4:

  • Maintain normal sensitivity of respiratory centres to change in oxygen and carbon dioxide concentration
  • Maintain normal cell oxygen use
  • Maintain a normal basal metabolic rate
  • Promote calorigenesis (heat production) by increasing metabolic rate of cells
  • Enhance the effects of the sympathetic nervous system
  • Promote glucose metabolism, fat mobilisation and protein synthesis
  • Maintain normal adult nervous system function
  • Promote normal cardiac function to include rate and force of contraction
  • Promote normal muscle development and function, skeletal growth and maturation
  • Promote normal gastrointestinal motility, tone, enzyme secretion
  • Maintain hydration and secretory function of the skin

These effects, when magnified lead to clinical signs and symptoms experienced by patients.

Learning bite

Thyrotoxic crisis typically occurs in patients in whom pre-existing hyperthyroidism has not been diagnosed or has been treated insufficiently.[4]