Superior parathyroid gland

At a glance

English

Superior parathyroid gland

Latin (TA2)

Glandula parathyroidea superior

System

Endocrine gland

Region

Whole body

Side

Paired, left and right

About the superior parathyroid gland

The superior parathyroid glands are the upper pair of the usual four parathyroid glands. Each is a small, flattened, tan-coloured oval a few millimetres long, set against the posterior surface of the thyroid's lateral lobe at about its midpoint. A common landmark is the level of the lower border of the cricoid cartilage, close to where the recurrent laryngeal nerve passes up beneath the inferior constrictor to enter the larynx. Here the gland usually lies behind the nerve and above the inferior thyroid artery.

These glands develop from the fourth pharyngeal pouch, alongside the tissue that forms the parafollicular cells of the thyroid. Because they travel only a short distance with the thyroid as it settles in the neck, their position is far more predictable than that of the inferior glands, which descend with the thymus. Even so, they can sometimes lie behind the pharynx or oesophagus, or within the thyroid capsule itself.

In structure and function they match the inferior glands. Packed cords of chief cells, with scattered oxyphil cells and fat, release parathyroid hormone in response to a fall in blood calcium. The hormone mobilises calcium from bone, reduces its loss in the urine and drives the kidney to make active vitamin D, which increases calcium uptake from the intestine; at the same time it makes the kidney excrete more phosphate.

Surgeons look for the superior glands during thyroidectomy and parathyroid operations, using their fairly fixed site near the cricothyroid region as a guide. Damage to them or to their small arteries can cause hypocalcaemia after surgery, while an enlarged, overactive gland produces primary hyperparathyroidism with high calcium, renal stones and weakened bones.

Function and supply

Function

Secretes parathyroid hormone, which keeps blood calcium up by acting on bone, kidney and, via vitamin D, intestinal absorption.

Nerve supply

Sympathetic fibres from the cervical ganglia travel with its arteries; hormone release responds to blood calcium rather than to nerve input.

Blood supply

Usually the inferior thyroid artery, sometimes with a contribution from the superior thyroid artery; drained by the thyroid veins.