Structure and Functions of Thyroid Gland

Thyroid Gland Structure

• The thyroid gland consists of two lobes located on either side of the trachea, connected by a thin flap of connective tissue called the isthmus.
• The gland is composed of follicles and stromal tissues.

Thyroid Hormone Synthesis

• Thyroid follicles are composed of follicular cells that synthesize two hormones: tetraiodothyronine (T4) and triiodothyronine (T3).
• Iodine is essential for the normal rate of hormone synthesis in the thyroid.

Effects of Iodine Deficiency

• Iodine deficiency in the diet results in hypothyroidism and enlargement of the thyroid gland, commonly known as goitre.
• Hypothyroidism during pregnancy leads to defective development and maturation of the growing baby, causing stunted growth (cretinism), mental retardation, low intelligence quotient, abnormal skin, deaf-mutism, etc.
• In adult women, hypothyroidism may cause menstrual cycles to become irregular.

Hyperthyroidism

• Cancer or nodules of the thyroid gland can increase the rate of synthesis and secretion of thyroid hormones to abnormal high levels, leading to hyperthyroidism.
• Exopthalmic goitre is a form of hyperthyroidism, characterized by enlargement of the thyroid gland, protrusion of the eyeballs, increased basal metabolic rate, and weight loss, also known as Graves' disease.

Functions of Thyroid Hormones

• Thyroid hormones regulate the basal metabolic rate.
• They support the process of red blood cell formation.
• They control the metabolism of carbohydrates, proteins, and fats.
• They influence the maintenance of water and electrolyte balance.

Thyrocalcitonin (TCT)

• The thyroid gland secretes a protein hormone called thyrocalcitonin (TCT), which regulates blood calcium levels.