There is one receptor for thyroid hormone in the hypothalamus and pituitary and

Question

There is one receptor for thyroid hormone in the hypothalamus and pituitary and a different one in the periphery (the rest of the tissues in the body). Imagine that there is a loss of function mutation in the hypothalamic/pituitary receptor so that it is not functional but the receptor in the periphery is normal. Will each of these hormones be higher than normal, normal or lower than normal: TRH, TSH and thyroxine (T4)? Explain your answer. Will the metabolism of the person with this receptor abnormality be over-active, normal or underactive? Explain your answer.

Explanation / Answer

Hypothalamus secrete thyrotropin releasing hormone (TRH) which stimulates anterior pituitary to release thyroid stimulating hormone (TSH). TSH acts on the thyroid follicles to release the thyroid hormones T3 and T4. Thyroid hormones T3 and T4 exert negative feedback effect on hypothalamus and pituitary gland.

When hypothalamic/pituitary receptors are not functional, T3 and T4 cannot exert their negative feedback effect. So, the levels of TRH, TSH and T4 will be high and the metabolism of this person will be abnormally over-active.

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