Dr. Sheldon Rubenfeld Board Certified in Internal Medicine and in Endocrinology, Diabetes, and Metabolism

What Is the Thyroid Gland?

The thyroid gland is an endocrine or hormone-secreting gland located in the neck. Its functions are production, storage, and secretion of two thyroid hormone - thyroxine (T4) and triiodothyronine (T3). Thyroid hormones regulate the body’s use of energy. Too little hormone in the blood is hypothyroidism. Too much thyroid hormone in the blood is hyperthyroidism.

The normal thyroid gland, which is shaped like a butterfly, has two lobes connected by an isthmus and occasionally, a small pyramidal lobe rising upward from the isthmus. The thyroid gland is located in the lower part of the neck, in front of the windpipe (trachea). The thyroid gland moves with swallowing and is often visible, especially when it becomes enlarged.  Understandably, the thyroid gland is more easily seen in people with long, thin necks than in people with short, thick necks. Ordinarily, the thyroid gland weighs less than an ounce and has the consistency of muscle. The right lobe of the thyroid gland is often slightly larger than the left lobe.

When viewed under the microscope, the thyroid gland is composed of distinct units called follicles. Follicles make and store thyroid hormone. Follicles store thyroid hormones attached to a protein called thyroglobulin (Tg). Malignant tumors arising from follicular cells are called differentiated (papillary or follicular) or undifferentiated (anaplastic) thyroid cancer.