parathyroid gland
Meaning of parathyroid gland: Four glands the size of a grain of rice that hold the calcium level in the blood steady from hour to hour.
Definition of parathyroid gland
A parathyroid gland is one of four tiny glands, each about the size of a grain of rice, sitting on the back surface of the thyroid in the neck. Their single job is to keep calcium in the blood within a narrow range. They do it by releasing parathyroid hormone, which pulls calcium from bone, recovers it from the kidney, and increases how much is absorbed from food.
How do they control calcium?
Each gland carries a sensor on its surface that reads the calcium level in blood flowing past. When the level dips, the glands release more parathyroid hormone. The hormone acts in three places at once: it prompts bone to release stored calcium, tells the kidney to reclaim calcium that would have been lost in urine, and switches on the kidney enzyme that turns vitamin D into its active form, which in turn increases absorption from the gut. When calcium rises, hormone release falls away. The result is a thermostat, correcting in both directions within minutes.
What happens when they make too much or too little?
| Overactive | Underactive | |
|---|---|---|
| Blood calcium | High | Low |
| Typical cause | A benign growth in one gland | Injury or removal during neck surgery |
| Effects | Kidney stones, bone thinning, thirst, confusion | Tingling around the mouth and fingers, muscle cramps and spasm |
Why are they easy to damage?
They are small, pale and easily mistaken for fat or lymph tissue, and they sit directly behind the thyroid gland. Surgery on the thyroid therefore risks removing them or interrupting their delicate blood supply, and a fall in calcium in the days after such an operation is a recognized complication. Their number and position vary between people: some have three, some five, and a gland may lie low in the chest, which can make an overactive one hard to locate. Imaging that picks up the more active tissue is used to find it before surgery.
Are they related to the thyroid?
Only by address. The thyroid sets the pace of metabolism throughout the body, while the parathyroids do nothing but regulate calcium. The two glands arise from different tissue in the embryo and their hormones act on different targets. The similarity of the names causes persistent confusion in notes and in conversation.
Also known as
Used in a sentence
A single enlarged parathyroid gland was localized on imaging and removed.
Good to know
Despite the shared name and location the parathyroids have no role in metabolism, and their loss during thyroid surgery causes a fall in blood calcium rather than any thyroid symptom.
Word origin
Where “parathyroid gland” comes from
From the Greek para, meaning beside, joined to thyroid, so the glands lying beside the thyroid.