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Anatomy and physiology of the parathyroid gland
Parathyroid glands are part of the body’s endocrine systemendocrine systemThe group of glands and cells in the body that make and release hormones (which control many functions such as growth, reproduction, sleep, hunger and metabolism) into the blood.. They are located in the neck or upper chest near the thyroid. Like all parts of the endocrine system, the parathyroid glands play an important role in the body.
The parathyroid glands are pea-sized masses of glandular tissue. Generally, there are 4 parathyroid glands – 2 on each side of the thyroid. They are most often found on the back (posterior) surface of the thyroid, but may occasionally be inside the thyroid. Sometimes more parathyroid glands are present and may be located in other parts of the neck or the mediastinum (the space in the chest between the lungs, breastbone and spine).
The parathyroid glands make parathyroid hormone (PTH or parathormone). PTH regulates the calcium level in the blood.
Regulation of blood calcium level
PTH and calcitonin (a hormone secreted by the thyroid) interact to maintain the calcium level within a narrow range.
PTH acts to increase blood levels of calcium.
- When the blood calcium level falls below a certain level, the parathyroid glands secrete PTH, which stimulates osteoclasts (bone destruction cells) to break down bone and release calcium into the blood.
- PTH also acts on the kidneys and intestines to make them absorb more calcium, rather than release it.
Calcitonin acts to decrease blood levels of calcium.
- When the blood calcium level rises above a certain point, the thyroid secretes calcitonin, which causes calcium to be deposited in the bones.