Along the lateral lobes of the thyroid gland, the posterior portion is covered with small, flat parathyroid glands. There are 4 parathyroid glands, set aside in pairs of superior and inferior. These glands appear to be a combination of yellow and brown and measure anywhere from 3 to 8 millimeters long, 2 to 5 millimeters wide, and 1 1 millimeters in depth.
Two variations of epithelial cells comprise the parathyroid gland on a microscopic level. Principle cells, which are responsible for creating parathyroid hormones, are intermingled with oxyphil cells. The main job of the oxyphil cells is to provide support for main principle cells while also successfully provide a reserve supply of parathyroid hormone. Parathyroid glands receive a near identical blood supply and a near identical venous drainage as the thyroid glands. Innervation of the parathyroid glands varies from the thyroid glands. The vagus nerves send off pharyngeal branches so that the neurons reach the parathyroid glands. Neurons from the cervical sympathetic ganglia also are driven to the parathyroid glands.
The parathyroid glands are only responsible for the release of one hormone, the parathyroid hormone. The thyroid gland releases a hormone responsible for lowering blood calcium levels known as calcitonin while the parathyroid glands administer a counter acting hormone responsible for raising the blood calcium levels by presenting action to the body’s bones, small intestines, and kidneys.