Parathyroid glands

In this note, we will discuss the anatomy and function of the parathyroid glands (glandulae parathyreoideae). These are small circular endocrine glands that produce parathyroid hormone.

Anatomy and function of the parathyroid glands

The parathyroid glands are located on the posterior surface of the thyroid gland, within its fibrous capsule. There are typically four glands – two superior and two inferior, although the number can vary from 2 to 8.

Superior parathyroid gland (glandula parathyreoidea superior) - lateral aspect

Superior parathyroid gland (glandula parathyreoidea superior) - posterior aspect

Inferior parathyroid gland (glandula parathyreoidea inferior) - lateral aspect

Inferior parathyroid gland (glandula parathyreoidea inferior) - posterior aspect

The superior glands are generally located at the level of the lower border of the cricoid cartilage (cartilago cricoidea), and the inferior glands at the level of the lower pole of the thyroid gland.

As previously mentioned, the parathyroid glands produce parathyroid hormone (PTH or parathormone). Its main effect is the increase in blood calcium levels, which makes this hormone an antagonist to thyrocalcitonin.

Blood supply and innervation of the parathyroid glands

Arterial blood is supplied to the parathyroid glands primarily from branches of the inferior thyroid artery (a. thyroidea inferior).

However, due to the frequent variability of the anatomical position of the glands, the blood supply can also come from the inferior thyroid artery itself, the thyroid ima, the inferior laryngeal, and the tracheal and esophageal arteries.

Venous drainage from the parathyroid glands is provided by the parathyroid veins, which drain into the superior thyroid vein (v. thyroidea superior),

Superior thyroid vein (v. thyroidea superior)

the middle thyroid vein (v. thyroidea media),

and the inferior thyroid vein (v. thyroidea inferior)

The innervation of the parathyroid glands is primarily provided by the sympathetic nervous system, specifically by nerves originating from the superior, middle, and inferior cervical ganglia.

Glossary