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Question 1

How is the amount of thyroxine controlled?

Answer 1

. Low levels of thyroxine in the blood plasma are detected by the hypothalamus (in the brain)
. the hypothalamus releases TRH which stimulates the anterior pituitary gland to secrete TSH
. the TSH will then be carried in the bloodstream and stimulate the thyroid gland to secrete thyroxine
. once the thyroxine levels in the blood get too high, the hypothalamus will detect this and stops the production of TRH
. This will inhibit the anterior pituitary gland from releasing TSH
. this will therefore stop the production of thyroxine at the thyroid gland
- this end part is called negative feedback