Thyroid stimulating hormone is a pituitary hormone that helps control the body's metabolism, reports WebMD. TSH is created when the hypothalamus releases thyrotropin-releasing hormone, and TRH in turn prompts the pituitary gland to manufacture and release TSH.
TSH prompts the thyroid to create the hormones triiodothyronine and thyroxine, also known as T3 and T4; these hormones help control the body's metabolism, states WebMD. T3 and T4 are integral to normal brain development, and babies whose brains do not produce enough thyroid hormone may become mentally retarded. These hormones continue to play a prominent role in childhood and adolescent brain development.
Normal TSH levels in children range from 0.7 to 6.4 microunits per milliliter, and adults typically range from 0.4 to 4.2 microunits per milliliter, states WebMD. High TSH levels may result from an underactive thyroid or a pituitary gland tumor. An underactive thyroid can cause weight gain, dry skin, constipation, a feeling of being too cold and tiredness. Low TSH levels may result from an overactive thyroid gland, a goiter, damage to the pituitary gland or pregnancy during the first trimester. An overactive thyroid can cause weight loss, rapid heart rate, diarrhea, a feeling of being too hot or nervousness.