The Mechanics of Thyroid Hormone Secretion
The thyroid hormones T4 & T3 are secreted from the thyroid gland under the control of the hormone called TSH (Thyroid Stimulating Hormone) released from the anterior part of the pituitary gland situated just below the Hypothalamus in the brain. The TSH is in turn controlled by the hormone TRH (thyrotropin releasing hormone) secreted by the hypothalamus. When there is enough T4 & T3 in circulation a negative feedback is sent to the pituitary and the hypothalamus to stop the stimulus signal and thus the over production of these hormones are limited and controlled. The whole system works in a rhythm and so does the actions exerted by the thyroid hormones on the target tissue.
Hyperthyroidism: A situation where the thyroid gland starts functioning autonomously and continuously producing T4 & T3 in excess, beyond or irrespective of the control of the brain.
Hypothyroidism: A situation when the production of T4 & T3 hormones by the thyroid gland is subnormal, due to any reason. The reasons could be Thyroiditis, Iodine deficiency, surgical removal of the gland or destruction of the gland due to any cause. There could also be other reasons like birth defects in children or central hypothyroidism due to the lack of production of pituitary hormones like TSH or lack of effectiveness of produced hormones due to some defect.
What ever the cause the effects of Hyperthyroidism & Hypothyroidism are as follows:
Article compiled by Dr Ajith Joy K, email: firstname.lastname@example.org