thyroid
thyroid physiology and hormones
introduction
the hypothalamus releases thyrotropin releasing hormone (TRH)
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TSH stimulates the thyroid to produce
thyroxine (T4)
T4 is converted peripherally to T3 which is more active than T4
T3 binds to nuclear receptor proteins that function as transcription factors to regulate the expression of many genes. Nongenomic actions of thyroid hormone also regulate important physiologic parameters.
T4 inhibits further release of TRH and TSH in a negative feedback loop
testing for thyroid disease
patients with
hyperthyroidism generally have a low TSH, while those with
hypothyroidism generally have a high TSH, thus, for most patients a TSH is all that is needed to screen for thyroid disorder.
high pre-test probability patients with a normal TSH should also have a free T4 level performed, while those with suspected hyperthyroidism with a low TSH but normal free T4, should have T3 testing added.
screening in patients with
atrial fibrillation is low yield with clinical hyperthyroidism being present in ~1% while clinical hypothyroidism is present in ~1.5%
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thyroid.txt · Last modified: 2014/05/11 22:44 (external edit)