. Explain briefly Thyroid Gland and its Hormones
Thyroid Gland and its Hormones
Thyroid is butterfly-shaped gland that straddles on either side of upper part of trachea below larynx. The right and left lateral lobes lie on either side. Connecting the lobes is a mass of tissue, called isthmus. The thyroid gland consists of microscopic spherical sacs, called thyroid follicles. These contain colloid, composed of the glycoprotein thyroglobulin, which fill most of the thyroid gland. The wall of each follicle consists of two types of cells. Under the influence of TSH, the follicular cells synthesis thyroxine, which is also called T4 because it contains four atoms of iodine, and tri-iodothyronine or T3, which contains three atoms of iodine. T3 is more active and several times more potent than T4, but it is secreted in smaller amounts. T4 is converted to T3 by removal of one iodine. Because T4 and T3 have virtually identical effects on the target cells, they are usually considered together under the designation thyroid hormone or TH.