The thyroid is a small, butterfly-shaped gland located at the base of the front of the neck, just below the Adam’s apple. It secretes thyroid hormones that are responsible for:

• Increasing metabolism and oxygen consumption
• Enhancing heat production (calorigenic effect)
• Stimulating the nervous system
• Contributing to growth and development

Thyroid hormones also have critical roles in early brain development, somatic growth, bone maturation, protein synthesis and regulating production of red blood cells, and are regulated by the hypothalamic-pituitary-thyroid axis in the following sequence: 

1. The hypothalamus secretes thyrotropin releasing hormone (TRH) in a tropic fashion that activates the anterior pituitary to secrete thyroid stimulating hormone (TSH). 
2. TSH targets the thyroid and elevates thyroid hormone production. 
3. The thyroid secretes the hormones thyroxine or tetraiodothyronine (T4) and triiodothyronine (T3), which mediate the metabolic rate (how quickly the body uses and stores energy). 
4. T4 converts to T3 and RT3 (reverse T3). It is free T3 that turns on the ATP-making (metabolic) machinery inside each living cell, while the RT3 slows it down.
5. When adequate thyroid hormones are produced and secreted, the anterior pituitary stops secreting TSH via a negative feedback mechanism.

Thyroid function is very complex and exerts a profound effect on the function of nearly every other organ in the body. Therefore, smooth functioning of the overall body chemistry depends on the health of your thyroid gland.