triiodothyronin

Triiodothyronine, often abbreviated as T3, is a thyroid hormone that plays a crucial role in regulating the body's metabolism. It is one of two major hormones produced by the thyroid gland, the other being thyroxine (T4). T3 is the more potent and biologically active form of the two.

The thyroid gland produces both T4 and T3, but primarily T4. T4 is then converted into T3 in various tissues throughout the body, such as the liver, kidneys, and brain. This conversion is a key step in activating the thyroid hormones' effects. T3 circulates in the bloodstream, bound to transport proteins, and is taken up by cells. Once inside the cells, it binds to nuclear receptors, influencing gene expression and thereby affecting a wide range of physiological processes.

The functions of T3 are diverse and essential for normal development and function. It increases the basal metabolic rate, which is the amount of energy the body expends at rest. This leads to increased oxygen consumption, heat production, and the breakdown of carbohydrates, fats, and proteins for energy. T3 is also vital for growth and development, particularly in the nervous system and skeletal system during childhood. It influences heart rate and contractility, contributing to cardiovascular function. Furthermore, T3 affects mood, cognitive function, and the sensitivity of the body to other hormones.

Disruptions in T3 levels, whether too high (hyperthyroidism) or too low (hypothyroidism), can lead to significant health problems. Monitoring T3 levels is an important part of diagnosing and managing thyroid disorders.