Parathyroid gland

Parathyroid glands
Diagram showing structures in the human neck. The four green shaded areas represent the most common position of the parathyroid glands, which are generally four in number and situated behind the lateral lobes of the thyroid gland (shaded orange).
Thyroid and parathyroids as viewed from the back of the neck
Details
Precursor	neural crest mesenchyme and third and fourth pharyngeal pouch endoderm
System	Endocrine
Artery	superior thyroid artery, inferior thyroid artery,
Vein	superior thyroid vein, middle thyroid vein, inferior thyroid vein,
Nerve	middle cervical ganglion, inferior cervical ganglion
Lymph	pretracheal, prelaryngeal, jugulodigastric lymph nodes
Identifiers
Latin	glandula parathyreoidea inferior, glandula parathyreoidea superior
MeSH	A06.407.560
Dorlands /Elsevier	g_06
TA	A11.4.00.001
FMA	13890
Anatomical terminology []

Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods that produce parathyroid hormone. Humans usually have four parathyroid glands, variably located on the back of the thyroid gland — considerable variation exists. Parathyroid hormone and calcitonin (one of the hormones made by the thyroid gland) have key roles in regulating the amount of calcium in the blood and within the bones.

Parathyroid glands share a similar blood supply, venous drainage, and lymphatic drainage to the thyroid glands. Parathyroid glands are derived from the epithelial lining of the third and fourth branchial pouches, with the superior glands arising from the fourth pouch, and the inferior glands arising from the higher third pouch. The relative position of the inferior and superior glands, which are named according to their final location, changes because of the migration of embryological tissues.

Hyperparathyroidism and hypoparathyroidism, characterized by alterations in the blood calcium levels and bone metabolism, are states of surplus or insufficient parathyroid function.

The parathyroid glands are two pairs of glands usually positioned behind the left and right lobes of the thyroid. Each gland is a yellowish-brown flat ovoid that resembles a lentil seed, usually about 6 mm long and 3 to 4 mm wide, and 1 to 2 mm anteroposteriorly. There are typically four parathyroid glands. The two parathyroid glands on each side which are positioned higher are called the superior parathyroid glands, while the lower two are called the inferior parathyroid glands. Healthy parathyroid glands generally weigh about 30 mg in men and 35 mg in women. These glands are not visible or able to be felt during examination of the neck.

The blood supply, drainage, and lymphatic drainage of the parathyroid glands correspond to the thyroid overlying gland.

The superior parathyroid glands receive their blood from the inferior thyroid arteries. The inferior parathyroid glands receive a variable blood supply, from either the ascending branch of the inferior thyroid arteries or the thyroid ima artery. The inferior thyroid artery arises from the subclavian arteries.