Parathyroid gland

Origin: two inferior glands derive from the third branchial pouch, two superior glands, from the fourth branchial pourch.

Location: on the posterior surface of the thyroid gland.

Function: parathyroid hormone (parathormone, PTH) regulates calcium and phosphate levels in the blood. It stimulates bone resorption, kidney excretion of phosphate, intestinal absorption of calcium, and reduces kidney excretion of calcium.

Composition: cords of parathyrocytes surrounded by thin connective tissue and rich networks of fenestrated capillaries.

Function: secretion of parathyroid hormone.