Each of the four parathyroid glands measures approximately 3 to 4 millimeters in diameter and is roughly the size of a grain of rice, according to the American Association of Endocrine Surgeons. These glands are located behind the thyroid gland in the neck.
The parathyroid glands are referred to as the right superior, right inferior, left superior and left inferior, and they produce a hormone that regulates the amount of calcium in bones and blood, notes InnerBody. If a particular parathyroid gland goes bad, it typically becomes engorged in size, as the Norman Parathyroid Center explains. When this happens, the gland produces too much of the parathyroid hormone, leaching the calcium from the bones into the blood and leading to osteoporosis. When a parathyroid gland goes bad, it is best to have it surgically removed.