Four small glands studded on the back of a butterfly-shaped neck gland, each the size of a grain of rice
Parathyroid glands — 'para' means beside, and they lie beside the thyroid.
Anatomy · Glands & the immune system
Parathyroid glands
Usually four, each about the size of a grain of rice
Endocrine system · back of the thyroid
Usually four tiny glands, two on the back of each lobe of the thyroid in the neck, though people may have more or fewer. Despite the name and the neighbourhood they are unrelated to the thyroid. They make parathyroid hormone (PTH), the body's main regulator of blood calcium: PTH releases calcium from bone, holds on to it in the kidneys and activates vitamin D. They were the last major endocrine glands to be discovered in humans.
How to spot them
- ▸Small yellow-brown oval nodules, each only a few millimetres across, on the back of the thyroid lobes
- ▸Two upper and two lower on each side, lying behind the thyroid
- ▸Under the microscope, sheets of small dark chief cells with scattered larger pink oxyphil cells and fat cells between
- ▸Supplied mostly by the inferior thyroid artery
What to know
The body's principal hormonal defence against low blood calcium
Parathyroid glands — parathyroid hormone, PTH.
A Swedish medical student in Uppsala gave the first description in humans in 1880 (1880)
Parathyroid glands — Ivar Sandström, who named them 'glandulae parathyroideae'.
Sheets of small dark cells with a few larger pink cells, seen through the microscope, among fat
Parathyroid glands — chief cells make the hormone; oxyphil cells are larger and pink.
Accidental removal of these during neck surgery can cause tingling, cramps and carpopedal spasm from low calcium
Parathyroid glands — hypoparathyroidism gives low calcium and tetany.
Overactivity classically leads to 'stones, bones, groans and moans'
Parathyroid glands — hyperparathyroidism causes high calcium, kidney stones and bone loss.
The lower pair develops from the third pharyngeal pouch, the upper pair from the fourth
Parathyroid glands — counter-intuitively the lower ones come from the higher pouch.
Key ideas
- When blood calcium falls, the chief cells release PTH. It stimulates bone-resorbing osteoclasts, reduces calcium loss in the urine, and activates vitamin D so the gut absorbs more calcium.
- When calcium rises, PTH release is switched off. The cells sense calcium directly through a calcium-sensing receptor, without needing a signal from the pituitary.
Quick-fire facts
- •Most people have four, but some have five or more, and the glands can lie in unexpected places such as inside the thyroid or near the thymus
- •Each weighs only around 30–50 mg
- •Ivar Sandström (1880) gave the first full description in humans; Richard Owen had earlier described them in an Indian rhinoceros in 1852
- •The first successful parathyroidectomy for hyperparathyroidism was performed by Felix Mandl in Vienna in 1925
- •PTH and calcitonin (from the thyroid's C cells) act in opposite directions; PTH is the more important regulator in humans
- •PTH raises blood calcium and lowers blood phosphate, by increasing phosphate loss in the urine
- •Low calcium after surgery may show as Chvostek's sign (facial twitch on tapping) or Trousseau's sign (hand spasm under a blood-pressure cuff)
- •The superior glands come from the fourth pharyngeal pouch; the inferior glands from the third, together with the thymus
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