The thyroid gland is a butterfly-shaped endocrine gland that is normally located
in the neck inferior to (below) the thyroid cartilage (also known as the Adam's apple
in men) and at approximately the same level as the cricoid cartilage (the lower front
of the neck). The thyroid’s function is to make thyroid hormone.
The main thyroid hormone is thyroxine, also called T4 because it contains four iodine
molecules. Thyroid hormone is transported to every tissue in the body and is essential
to support every cell in each tissue and organs for them to function correctly.
For example, thyroid hormone helps the body use energy, stay warm, and keep the brain,
heart, muscles, and other organs working as they should.
The thyroid gland is one of the largest endocrine glands in the body it is controlled
by the hypothalamus and pituitary. The gland gets its name from the Greek word for
"shield", after the shape of the related thyroid cartilage.
The thyroid controls how quickly the body uses energy, makes proteins, and controls
how sensitive the body should be to other hormones. The thyroid participates in these
processes by producing thyroid hormones, principally thyroxine (T4) and triiodothyronine
(T3). These hormones regulate the rate of metabolism and affect the growth and rate
of function of many other systems in the body. Iodine and tyrosine are used to form
both T3 and T4.
The thyroid also produces the hormone calcitonin, which plays a role in calcium homeostasis.
Hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid) are
the most common problems of the thyroid gland.
