The thyroid gland is a crucial hormonal gland that plays an important role in growth and development, metabolism and regulating several functions of the human body such as temperature and calcium balance. It constantly secretes, stores and releases multiple hormones, collectively referred to as thyroid hormones.
A sufficient supply of thyroid hormones is important for brain development during childhood and infancy. The major hormones secreted by the thyroid glands are T4 (levothyroxine) and T3 (liothyronine); they affect virtually every cell in the human body, and help regulate human body functions. T4 and T3 are produced in the follicular epithelial cells of the thyroid gland; their main component is iodine. While some of the hormones produced by the thyroid gland are stored as droplets, others are joined to carrier proteins in the blood.
The thyroid gland is found at the base of the neck, immediately below the Adam's apple. It has a butterfly shape, with each wing lying on either side of the windpipe. The most common medical condition associated with the thyroid gland is hypothyroidism, which occurs when too little hormone is secreted. Hyperthyroidism occurs when too much hormone is produced. Other conditions associated with the thyroid gland include thyroiditis, goiter, Grave's disease, thyroid cancer, thyroid storm and thyroid nodule.