Thyroid gland

(1) The name "thyroid" was introduced by Thomas Wharton (1656).

(2) It is derived from Greek "Thyreos" a shield.

(3) Location: This is the largest endocrine gland of our body. It is located in our neck upon the ventral aspect of larynx (sound box or Adam's apple) and a few anterior most tracheal rings. It is a dark brown and H-shaped bilobed gland.

(4) Hormones of thyroid:

Thyroid gland secretes two iodinated hormones.

(a) Thyroxine: It is an iodine containing (6% iodine) amine hormone which is derived from tyrosine amino acid. Chemically thyroxine is tetraidothyronine though also found as tri-iodothyronine. Secretion of thyroxine is inversely proportional to the blood level of thyroxine (feedback mechanism).

(b) Thyrocalcitonin (TCT): It is a long peptide hormone secreted by parafollicular by cells of thyroid gland (C-cells). It secretion is regulated by increased plasma level of calcium by feedback mechanism.

(5) Irregularities of thyroid gland

(a) Hypothyroidism: (Decreased section of thyroxine from thyroid gland).

(b) Hypersecretion of thyroid hormones (Hyperthyroidism or thyrotoxicosis) : This may also be a genetic defect, but usually it is provided by chronic infections (influenza, rheumatism, tonsilitis, tuberculosis, measles, whooping cough, etc.) pregnancy, intake of large doses of iodine, over-eating, etc. It results into a considerable increase in glucose and oxygen consumption by cells and the rate of oxidative metabolism in the mitochondria.