The parathyroid gland is an endocrine gland. Endocrine glands produce proteins called hormones, which travel in the blood to act on the cells of tissues in different parts of the body. An individual normally has four parathyroid glands, resembling yellow grains of rice, which are in the neck, close to the thyroid gland. Parathyroid function involves the production of what is known as parathyroid hormone, which regulates calcium levels in the blood. When blood calcium levels fall, the parathyroid glands produce more parathyroid hormone, which acts to raise blood calcium and restore it to the normal range.
Parathyroid hormone elevates the level of calcium in the blood in a number of different ways. The hormone stimulates the release of bone calcium, increases calcium absorption from the gut, and prevents the kidneys from removing calcium from the body in urine. As soon as these actions cause blood calcium to return to normal levels, parathyroid hormone production falls. In this way, parathyroid function enables the amount of calcium in the blood to be maintained within a narrow range.
Sometimes, illness causes parathyroid function to become abnormal. A parathyroid gland can become overactive, producing too much parathyroid hormone, due to the presence of a hormone-secreting tumor known as an adenoma. This condition is known as hyperparathyroidism and, if the subsequent rise in blood calcium is large, it can cause symptoms such as frequent urination, constipation, nausea and vomiting. Over time, the continuous release of calcium from bones may lead to them becoming brittle, with a risk of fractures. Stones might form in the kidneys and, more rarely, stomach ulcers and inflammation of the pancreas could occur.
Parathyroid function can also become underactive, in a disorder called hypoparathyroidism. This usually occurs as the result of surgery, where the parathyroid glands have either been removed intentionally or accidentally damaged. Symptoms of low parathyroid function include tingling sensations or muscle spasms in the hands and feet and seizures, or fits.
In the case of hyperparathyroidism, the abnormal parathyroid function is usually successfully treated by surgically removing the overactive gland. A technique known as minimally invasive parathyroid surgery is often used, which allows removal of the diseased gland through a small cut in the neck. Hypoparathyroidism can be managed using medication. A daily dose of vitamin D is taken, or a substance which the body can convert into vitamin D. Regular monitoring of blood calcium levels is necessary to determine the correct dose at first and, in the long term, to pick up any changes in the body's requirements.