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
#posting tugas cyberprenership
ahmad baihaqi
NIM 1112503964
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