||Thyroid stimulation hormone is secreted by pituitary gland in response to the stimulation of Thyrotropin Releasing Hormone (TRH) produced by hypothalamus. TSH binds to the TSH receptors on the surface of the follicular cells in thyroid and stimulates the production of thyroid hormones (T4 and T3). TSH, T3 and T4 play an important role in normal growth, brain development in young children, and regulate the metabolism in adults. TSH secretion is increased when T3 and T4 are insufficient. Elevated TSH, but low T3 and T4 levels indicate that thyroid cannot produce thyroid hormones at a normal rate and the condition is called hypothyroidism. If T3 and T4 levels are high when TSH is at a low level, it indicates that thyroid is producing abnormally large amount thyroid hormones, and the condition is called hyperthyroidism which is manifested by hypermetabolic symptoms.
TSH has a α subunit that is identical to the one in other glycoprotein hormones such as LH, FSH and HCG.