The thyroid hormones, thyroxine (T4) and triiodothyronine (T3), regulate many of the body’s essential functions, including energy production, metabolism, body temperature, heart rate and brain function. These hormones are produced by the thyroid gland under the control of thyroid stimulating hormone (TSH), which is released by the pituitary gland. 

Physiology 
The normal processes that keep your body functioning, including digestion, energy production, hormones, immunity and repair. Understanding physiology helps explain why symptoms occur and what needs to change for recovery.