What are the functions of the Thyroid Gland ?

It is a large, large, bilobed gland (2cm x 2 cm x 2cm) behind the larynx (voice –box) in the neck. Human thyroid weighs 25 g. Between the lobes is a connecting isthmus. It secretes thyroxine and thyrocalcitronin hormones. Thyroxine contains iodine atoms. Thyroxine controls the general metabolism of the body. Thyroxine accelerates energy production and oxygen consumption in the body. Thyroxine stimulates absorption of glucose in the intestine. Thyroxine promotes protein synthesis in the body. Lipid and cholesterol in the blood vary inversely with the level of thyroxine.

Excessive secretion of thyroxine increases the general metabolism of the body; as a result there is slight increase in body temperature. Fat stores in the body are depleted and there is a loss of body weight. There is a restlessness and protrusion of the eyeball. The heart rate is also increased. All these symptoms are characteristic of a disease known as Graves’ disease (named after an Irish physician, Robert James Graves).

If, on the other hand, thyroxine secretion is reduced or lowered it will lower general metabolism of the body. If this happens in the adult, he or she will have a swollen, puffy face. There may be loss of hair from armpits, eyebrows, etc. There may be swelling of the tongue and vocal cords giving rise to hoarseness of voice. The disease characterized by the above mentioned symptoms is called myxoedema. When thyroxine production decreases in children, their metabolism, general body growth and brain growth also retard. This condition is called cretin ism and the child suffering from this is termed cretin child.

The enlargement of thyroid gland is called goiter. As a result of this, the neck wells up. Swelling of thyroid may be due to deficiency in iodine. We get iodine from food and water. If these are deficient in iodine, we may suffer this condition. When thyroxine production is lowered due to iodine deficiency, we call it endemic goiter. When thyroid gland becomes excessively developed and secretes excess thyroxine, we call this goiter. Thyrocalcitonin is also a hormone secreted by thyroid gland which decreases the amount of calcium in the blood, by taking excess calcium to the bone.