It is the largest endocrine gland and is highly vascular. It lies on the ventral and lateral sides of the upper part of the trachea and neck.

Structure and Function

It is brownish red, shield shaped, bilobed gland. The two lobes are connected by a bridge of tissues calle isthmus. The lobes of the gland are made up of follicles or acini. They secrete a hormone called thyroxine derived from tyrosine, an iodinated amino acid.

Functions of Thyroxine

  • They control the rate of oxidation and production of energy by maintaining the Basal Metabolic Rate (BMR) of the body.
  • They control growth of physical, mental and sexual growth of the body. Growth of central nervous system and bones is regulated by thyroxine.
  • Regulates Iodine and sugar level in blood.
  • Control the working of kidneys and urine output.
  • Regulates carbohydrate and fat metabolism.

Improper secretion of the thyroxine hormones results in the following diseases. Increased secretion results in Hyperthyroidism and less secretion in Hypothyroidism.

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