Thyroid gland is an endocrine organ located in the front part of the neck, in front and both sides of the windpipe (trachea) and just in front of the voice box.  It is butterfly shaped organ consisting of right and left lobes that are connected in the middle by isthmus.
 
Thyroid gland produces thyroid hormones which have an effect on heart rate, breathing, weight, muscle strength, central and peripheral nervous system, body temperature, menstrual cycle and others.
 
Thyroid gland produces 2 hormones, triiodothyronine (T3) and thyroxine (T4).  Iodine in the diet is needed to produce these hormones.  It is important that T3 and T4 levels are within normal range, too little and too much is not good for our health and causes many problems.  Two glands in the brain, the hypothalamus and the pituitary gland, are also involved in maintaining normal balance of thyroid hormones.
 
The hypothalamus produces TSH Releasing Hormone (TRH) that signals to pituitary  to tell the thyroid gland to produce more or less of T3/T4 by either increasing or decreasing the release of thyroid stimulating hormone (TSH).  When T3 or T4 levels are low in the blood, the pituitary gland releases more TSH which will in turn increase the lecelv of thyroid hormones.  If T3/T4 levels are high, pituitary produces less TSH which will decrease the levels of thyroid hormones. 
 
T3 and T4 influence almost all cells in the body by influencing their metabolism, protein production and development.