Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

Special Part
Endocrine glands (ductless glands), glandulae endocrinae (glandulae sine ductibus)
Peripheral endocrine organs — Parathyroid glands

The Parathyroid glands, glandulae parathyroideae, are typically paired (two superior and two inferior) and located symmetrically on the posterior surface of The Thyroid Gland. Occasionally, their number may reach six. They appear as small, rounded structures with a thickness of 2–3 mm. The weight of each gland is about 50 mg; their surface is smooth, shiny, and has a yellowish-brown color. The outer surface of the parathyroid glands is enclosed by a Connective Tissue capsule, from which trabeculae extend into the parenchyma. The glandular parenchyma is composed of epithelial endocrine Cells known as parathyroid cells (parathyrocytes).

Function. The parathyroid glands produce parathyroid hormone (parathormone). It stimulates The activity of osteoclasts, which break down the Extracellular matrix of Bone tissue, thereby increasing the concentration of calcium salts in the Blood. An excess of parathormone affects the nephron tubules, leading to the inhibition of calcium reabsorption from the primary urine. Simultaneously, bone changes occur due to heightened osteoclast activity, resulting in the destruction of bone tissue. This condition is known as generalized osteitis fibrosa cystica (Recklinghausen's disease).

Hypofunction of the parathyroid glands leads to involuntary twitching of individual Muscles, ultimately resulting in tetany. Spasms most frequently occur in the upper extremities, producing a characteristic hand posture known as the "obstetrician's hand". In some cases, this may be accompanied by laryngeal Muscle spasms and respiratory distress.

Blood supply. The parathyroid glands are supplied with blood by Branches of the superior and inferior thyroid Arteries, and occasionally by branches originating from the Thoracic Aorta (rami oesophagei, rami bronchiales). Venous drainage occurs into the venous plexuses of the thyroid gland. Lymph from the parathyroid glands drains via a system of lymphatic capillaries and vessels into the deep cervical, paratracheal, and mediastinal Lymph Nodes.

Innervation. Efferent Innervation of the parathyroid glands is provided by fibers from the cervical Sympathetic trunk and the Vagus nerve.