Answer
Thyroid gland is an endocrine gland that
releases hormones called thyroxine (T4) and
triiodothyronine (T3). TheSe hormones mainly functions to
regulate all the metabollic processes in the body.
Secretion of thyroid gland is regulated by a feedback control
mechanism.
- When levels of T3 and T44 are low in blood,
hypothalamus releases a regulatory hormone called
thyrotropin releasing hormone (TRH).
- TRH acts on anterior pituitary gland and
stimulates the release of a tropic hormone called thyroid
stimulating hormone (TSH).
- TSH acts on thyroid gland and stimulate
release of thyroxine (T4) and triiodothyronine
(T3).
- This increases the levels of T3 and T4 in the blood.
- When levels of T3 and T4 in the blood increases above normal
range, these hormones send a negative feedback
signal to the hypothalamus in order to inhibit secretion
of TRH.
- As a result anteior pituitary also inhibits TSH secretion.
- Due to lack of TSH stimulation, thyroid gland inhibits
production of T3 and T4.
- The levels of thyroid hormone decreases to normal range.