~ 1% have five or more glands (supernumerary).
~1% have < 4 glands.
One superior (higher along the thyroid, closer to the jaw) and one inferior (lower along the thyroid, closer to the collar bone) gland on each side.
Image Source: Mary Ann Liebert, Inc.
The parathyroid glands originate high in the neck, then migrate lower down the neck during development as a fetus.
During this migration, some parathyroid glands may over-descend (located lower than anticipated) or under-descend (located higher than anticipated).
More common in inferior glands given the longer path of descent and traveling along with the thymus which can drag the inferior parathyroid glands with it lower into the upper chest (mediastinum).
Small, loosely organized groups of parathyroid cells which are functional.
Most commonly located in the thymus (mediastinum).
Important when considering surgical options for Kidney Related Hyperparathyroidism.
Parathyroid chief cells – produce and store parathyroid hormone (PTH).
Oxyphil cells – thought to be support cells, true function is unknown.
Calcium is important for keeping bones and teeth strong, allowing muscles to contract, keeping your heart beating in a normal rhythm, and helping your brain send messages throughout the body via the nervous system, as well as many other vital functions.
Because of its essential nature, calcium levels need to be kept in a tight range, otherwise dysfunction throughout the body can occur if levels are too high or too low.
All four parathyroid glands are constantly measuring calcium levels in the blood.
When the calcium levels drop below a certain level (‘set point’ – varies slightly for all individuals), the parathyroid glands recognize this.
When the parathyroid glands function appropriately:
