Senin, 25 Maret 2013

Thyroid System

    Iodine deficient goiter, (enlargement of the thyroid gland) results because iodine is a crucial component of active thyroid hormones. If there is a low level of iodine in the diet, then less active T3 and T4 can be synthesized. As diagrammed in the figure, when there is less T3 and T4, there is reduced negative feedback inhibition on secretion of the tropic hormones, TRH (thyrotropin releasing hormone; released by the hypothalamus) and TSH (thyroid stimulating hormone or thyrotropin; released by the anterior pituitary). TSH stimulates all aspects of thyroid hormone synthesis; it also stimulates proliferation of follicle cells. When iodine in the diet is low but not too low, individuals may have goiter and yet be euthyroid, because the enlarged thyroid gland is better able to use the limited amount of iodine available. This is an example of hormonal homeostasis.

    Graves disease is the most common cause of hyperthyroidism. Graves disease is an autoimmune disorder in which antibodies are produced that bind to the TSH receptor. Instead of destroying the receptor, these antibodies activate it, stimulating synthesis of T3 and T4, and causing growth of the thyroid gland. Negative feedback inhibition is increased, so the levels of TRH and TSH decrease, but this does not decrease thyroid hormone production because the stimulation of the thyroid gland is independent of TSH. Measurement of low TSH levels is a key diagnostic test for hyperthyroidism

Sumber : Bpk. Dr. Iskandar Zulkarnain

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    ahmad baihaqi
    NIM 1112503964

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