Mechanism Showing How TSH Undertakes Two Roles. (IMAGE)

Institute of Transformative Bio-Molecules (ITbM), Nagoya University

Mechanism Showing How TSH Undertakes Two Roles.

Caption

TSH in pars distalis (PD-TSH) is controlled by the hypothalamus -- pituitary gland -- thyroid gland (HPT) axis. The hypothalamus secretes the thyrotropsin-releasing hormone (TRH), which stimulates the synthesis and secretion of PD-TSH. PD-TSH, then acts on the thyroid gland, which secretes thyroid hormones, T4 (precursor thyroxine) and T3 (bioactive triiodothyronine), and the expression of PD-TSH is controlled by negative feedback. On the other hand, TSH in pars tuberalis (PT-TSH) is not controlled by the HPT-axis but is regulated by melatonin, which is secreted by the pineal gland during the evening, and sends the message of spring to the hypothalamus. Both PT-TSH and PD-TSH are secreted into the bloodstream, but PT-TSH is trapped by immunoglobulin and albumin through its distinct carbohydrate chains leading to loss of bioactivity and thus, has no effect on the thyroid gland.

Credit

ITbM, Nagoya University

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