Thyroid-stimulating hormone (TSH) is produced by the pituitary gland and activates the thyroid gland to produce thyroxine (T4) and triiodothyronine (T3). T4 is converted to T3 in the liver and requires the presence of selenium and zinc.
T3 and T4 regulate the body's basal metabolic rate, influence heart and nervous system functions and are essential for growth and development. The thyroid gland also produces calcitonin which is essential in the regulation of calcium balance in the body. Thyroid hormones play a critical role in growth, differentiation and metabolism. Thyroid hormones are needed for the normal function of nearly all tissues of the body. They have a major effect on oxygen consumption and metabolic rate.
Disorders of the thyroid are among the most common diseases of the endocrine glands, particularly in women. Thyroid function tends to decreases with age. Hypothyroidism is particularly common in menopausal and post menopausal women.
Thyroid Dysfunction Symptoms
Symptoms of underactive thyroid include dry and course skin, weakness and lethargy, constipation, weight gains, slow pulse, feeling cold, heavy and irregular periods and depression. Symptoms of an over active thyroid of hyperthyroidism include fast metabolic rate, rapid heart beat (Tachycardia), nervousness, palpitations, weight loss despite increase appetite, feeling hot and frequent/loose bowel movements.
Thyroid Hormone Regulation
The synthesis of thyroid hormones and their secretion is regulated by a negative-feedback system that involves the hypothalamic, pituitary, and thyroid gland.
Thyrotropin releasing hormone (TRH) is a regulator hormone that binds to TRH receptors in the pituitary, this stimulates pituitary thyrotropes that produce Thyroid stimulating hormone (TSH).
TSH is the primary regulator of thyroid hormone release. It also plays a critical role in thyroid growth and development. TSH binds to the TSH receptor (TSHr). Activation of TSHr by TSH or autoantibodies in Graves' disease leads to an increase in intracellular cAMP and stimulation of protein kinase A-mediated pathways.
One blood specimen is required. This can be taken at your nearest Australian Clinical Lbas collection centre. Visit locations to find your nearest collection centre or phone 1300 554 580 between 9.00am and 5.00pm Monday to Friday for details on the location of your nearest centre.
Test results usually become available within 7-10 working days.
Patients does not need to fast or make any special preparation before having blood collected.
Patient results are delivered to the referring practitioner via electronic download unless requested otherwise. Results can also be issued via hardcopy, fax or web based e-viewer.