Thyroid gland is the largest endocrine gland in adult human. Endocrine glands are those that secrete their products directly into the bloodstream. In contrast, most exocrine glands release their secretions through a duct onto an epithelial surface such as skin or mucosa. Thyroid gland is made up of two lateral lobes joined together across midline by a narrow bridge of tissue called isthmus. It is relatively larger in women and children than in men.
Thyroid gland lies in the anterior part of our neck, immediately below the larynx and overlying the trachea (windpipe). A normal thyroid gland weighs between 25 and 40 gm. This butterfly shaped gland is highly vascular so it receives one of the highest rates of blood flow per gram of tissue. Thyroid gland moves with the larynx in swallowing and speaking - this feature helps a healthcare professional to differentiate swellings in the glands from those in the adjacent structures.
Iodine is essential for thyroid hormone synthesis. Dietary intake of about 150 microgram per day mainly in the form of iodide is typical to maintain normal thyroid hormone secretion. In many countries common table salt is iodized to prevent iodine deficiency. Iodine deficiency is the most common cause of goiter which is considered as one of the thyroid diseases.
⇛ Thyroid hormones are essential for normal growth and maturation. They play crucial role in the development of central nervous system (CNS). The most serious effect of thyroid hormone deficiency during childhood is permanent brain damage and dwarfism.
⇛ Thyroid hormones accelerate cholesterol clearance from the plasma.
⇛ Thyroid hormones are required for conversion of carotene to vitamin A; patients with hypothyroidism may suffer from night blindness.
⇛ Thyroid gland also releases a minor hormone called calcitonin which is involved in calcium and phosphate metabolism. Calcitonin stimulates cartilage growth and causes increased deposition of calcium in the bones therefore promoting bone formation and reducing calcium concentration from the blood.
