TSH is a regulatory hormone, that is, it functions to regulate thyroid hormone levels in the blood. This is accomplished through what's called a negative feedback mechanism. This negative feedback system is, in turn, orchestrated by a gland located at the base of the brain known as the hypothalamus. The hypothalamus, acting as a master gland oversees the body's levels of thyroid hormone. The hypothalamus assures that there will be sufficient thyroid hormone available for the body's needs.
Hormones are glycoprotein chemicals that cause action away from their point of origin.
For instance, thyroid hormone released by the thyroid gland, travels through the circulation and reacts with cells throughout the body, causing the production of energy. For example, thyroid hormone reacts with receptors in your skin, helping to maintain a normal temperature. The goose bumps that cool you off or your involuntary shivering are both caused by thyroid hormone's influences. In a similar fashion, the hormone TRH, released by the hypothalamus in the brain, exerts action on thyrocyte cells located in the pituitary gland. TSH, in turn, causes the follicular cells in the thyroid gland to produce and release thyroid hormone.