thyroid anatomy

Where is the parathyroid, and what does it do?

Parathyroid glands are located in the neck, on the thyroid gland. Most people have four pea-sized, oval-shaped parathyroid glands. Endocrine glands, such as the thyroid and parathyroid, secrete hormones, which are natural chemicals that regulate body functions. The job of the parathyroid is to secrete parathyroid hormone, which helps regulate how the body uses calcium.

Calcium is needed by cells in many parts of the body—the brain, heart, nerves, bones, and digestive system. parathyroid hormone satisfies these needs by taking calcium from bone, where it is stored, and releasing it into the blood stream. "Communication" between the parathyroid and blood stream help keep calcium at its normal level.

What is a parathyroid adenoma?

Sometimes, benign (noncancerous) growths called adenomas appear on one or more of a person's parathyroid glands. The cause of most parathyroid adenomas is unknown. However, about 10 percent are thought to be hereditary. Radiation exposure of the head and neck also may increase the risk of adenomas (as in the people who were exposed to the atomic bomb in Hiroshima).

Adenomas cause the parathyroid gland to make more parathyroid hormone than the body needs, a condition called primary hyperparathyroidism. Too much parathyroid hormone upsets the body's normal calcium balance, which increases the amount of calcium in the blood stream. A similar but less common condition, called secondary hyperparathyroidism, can occur in people with chronic kidney failure.

Approximately 100,000 Americans develop primary hyperparathyroidism each year. Women are twice as likely to develop parathyroid adenomas as men, and often after menopause. Primary hyperparathyroidism may be caused by one adenoma, more than one adenoma (hyperplasia), or cancer (which is very rare).