The Thyroid Gland
▶Anatomy of the Thyroid Gland
The thyroid gland lies near thyroid cartilage of the larynx and is known to be a butterfly in shape. It consists of two lobes connected by the isthmus. It has a rich blood supply. Also, it contains numerous thyroid follicles. It produces, store and releases thyroid hormones.
▶Thyroid Follicles and Thyroid Hormones
Thyroid Follicles produce and store colloid. Thyroid colloid consists of enzyme required for secretion of thyroid hormone. The production of colloid requires adequate iodine in the diet. The thyroid follicles lead to the production of thyroxine (T4) and triiodothyronine (T3). It increases metabolism and heat production (calorigenic effect) ie. it results in increased uptake of oxygen which increases the respiration rate and ultimately in ATP production.
▶C Cells of the Thyroid Gland
C cells are scattered outside of follicle epithelium known as parafollicular cells. It secretes calcitonin and lowers the blood Ca2+ levels. It also inhibits osteoclasts of bone. It gets triggered by the hypothalamus when there is low Ca2+ level in the body.
If there is a fall in Ca2+ levels in body, the thyroid gland is triggered. This leads to the production of Calcitonin in the thyroid gland which increases the release of calcium ions in the kidney and the calcium deposition in the bone which maintains homeostasis.
▶The Parathyroid Glands
Posterior Thyroid glands are embedded by four glands. The parathyroid gland is the chief cells that produce parathyroid hormone. Lower blood Ca2+ levels trigger the secretion of this hormone. PTH speeds bone breakdown by osteoclasts and increases dietary absorption• It is triggered by high Ca2+ levels in the body.
If there is an increase in Ca2+ levels in the body, the parathyroid gland is triggered. This leads to the release of the stored calcium from bone. This enhances the reabsorption of calcium in the kidney which balances the calcium in the body maintaining homeostasis.