Thyroid Gland: Hormones and functions

Thyroid gland: Hormones and functions

The gland is composed of two types of cells; follicular cell (secrete thyroid hormone) and para-follicular cell (secrete and store calcitonin hormone)

Location: in neck region on either side of trachea

Size: Each lobe is 4-6 cm long, and 1.5 cm thick

Hormones of Thyroid gland

  1. Thyroxine (Tri-Iodothyronine and tetra-Iodothyronine)

  • Increase basal metabolism rate by increasing O2 comsumption in most tissues except lungs, brain, testis and retina
  • Essential for growth of skeletal
  • Increase carbohydrate metabolism, promote gluconeogenesis
  • Effect on lipid metabolism
  • Stimulate NA-K ATPase.
  • Influence water and electrolyte balance.
  • It is regulated by TSH
  • At first T4 is synthesized which is converted to T3. T3 is five times more potent than T4.
  • Deficiency of thyroxine: Goiter, Hypothyroidism
  • Excess of thyroxine: thyrotoxicosis, hyperthyroidism.
  1. Calcitonin

  • It lowers calcium level in blood ( antagonistic to parathyroid hormone)

Thyroid gland: Hormones and functions


  1. Sir can u plz tell the location where parafollicular cell is present.Is it present on the wall of thyroid follicle .And is its secretion calcitonin also present in colloid along with synthesized T3 and T4

  2. Sir if T3 is much more active than T4 then why the level of T4 is more in blood than T3.Is it because it might work on the way before it reaches the target cell.And if its T3 that is more active does the T4 after reaching to target cell convert to T3?

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