The thyroid is a butterfly-shaped gland in the middle of the neck. It sits just below the larynx (voice box). The thyroid makes two hormones, called triiodothyronine (T3) and thyroxine (T4), which control how the body uses and stores energy. The parathyroid glands are four small glands behind the thyroid. They make a hormone called parathyroid hormone, which helps control the amount of calcium in the blood.