Thyroid gland

Thyroid Gland

The thyroid gland is one of the endocrine glands, which make hormones to regulate physiological functions in the human body. The thyroid gland manufactures thyroid hormone, which regulates the rate at which the body carries on its necessary functions. The thyroid gland is located in the middle of the lower neck, below the larynx (voice box) and just above your clavicles (collarbones). It is shaped like a "bow tie," having two halves (lobes): a right lobe and a left lobe joined by an "isthmus".

The thyroid gland contains numerous follicles, which are small spheres with their walls composed of a single layer of cuboidal epithelial cells. The center, or lumen, of each thyroid follicle is filled with a protein called thyroglobulin to which thyroid hormones are bound. The thyroglobulin stores large amounts of thyroid hormone.

Between the follicles a delicate network of loose connective tissue contains numerous capillaries. Scattered parafollicular cells are found between the follicles and among the cells that comprise the wall of the follicle. Calcitonin is secreted from the parafollicular cells and plays a role in reducing the concentration of calcium in the body fluids when calcium levels become elevated.

Diseases of the thyroid gland are very common. The most common diseases are caused by an over- or under-active glands. These conditions are called hyperthyroidism (e.g., Grave's disease) and hypothyroidism. Sometimes the thyroid gland can become enlarged from over-activity (as in Grave's disease) or from under-activity (as in hypothyroidism). An enlarged thyroid gland is often called a "goiter."

Patients may develop "lumps" or "masses" in their thyroid gland. They may appear gradually or very rapidly. Patients who had radiation therapy to the head or neck are more prone to develop thyroid malignancy.