Know about the Thyroid glands
- Thyroid gland is a small butterfly shaped gland (a gland is an organ or a group of cells in the body which secretes particular chemical substances), 2 inches in length, weighs 15-20 gms, located just under the skin below the Adam’s apple in the neck.
- Normally it cannot be seen but when it grows in size it can be easily seen as a prominent bulge (goiter) below or on the sides of the Adam’s apple.
- It produces hormones (a chemical substance) that regulate the body’s metabolism (body’s energy production) and organ function. It affects heart rate, cholesterol level, body weight, energy level, muscle strength, skin condition, vision, menstrual regularity, mental state and a host of other functions.
Thyroid needs iodine (an element found in water and food) for the synthesis of hormones. Thyroid hormones are found in two forms: Thyroxine (T4) and Triiodothyronine (T3). Most of the hormones are secreted in the form of thyroxine which is not metabolically active. Thyroxine is converted to the active form Triiodothyronine in liver, muscle or kidneys. T3 and T4 circulate in the blood almost entirely (99%) bound to transport proteins mainly thyroxine-binding globulin (TBG). It is only the minute fraction of free hormone, which enters the tissues and exerts its metabolic action.
Our body has a complex mechanism to adjust the levels of thyroid hormones. Production of thyroid hormones (T3 and T4) is stimulated by Thyrotropin (Thyroid Stimulating Hormone, TSH) secreted by anterior pituitary (‘master gland’ located in brain) in response to Thyrotropin- Releasing Hormone (TRH) secreted by the hypothalamus (located just above the pituitary gland in the brain). There is a feedback mechanism to keep the blood levels of thyroid hormones within normal limits (i.e. when the amount of thyroid hormones (T3 and T4) circulating in the blood increases, a feedback is sent to the pituitary which acts by producing less of TSH thereby adjusting the level of thyroid hormones accordingly, to normal).