Anatomy of the Parathyroid Glands

USMLE Guide

Introduction

The parathyroid glands are small endocrine glands located in the neck, adjacent to the thyroid gland. These glands play a crucial role in maintaining calcium and phosphorus balance in the body. In this article, we will delve into the anatomy of the parathyroid glands, their structure, and their function.

Key Takeaways

• Parathyroid glands are small endocrine glands located near the thyroid gland.
• There are usually four parathyroid glands, with two on each side of the thyroid.
• Parathyroid glands secrete parathyroid hormone (PTH) which regulates calcium and phosphorus levels.
• Understanding the anatomy of parathyroid glands is essential for diagnosing and treating related disorders.

Anatomical Location

The parathyroid glands are typically four in number, with two located on each side of the thyroid gland. They are usually described in relation to their position relative to the thyroid lobes.

• Superior parathyroid glands: Located superiorly to the upper poles of the thyroid lobes.
• Inferior parathyroid glands: Located inferiorly to the lower poles of the thyroid lobes.

Structure of Parathyroid Glands

Each parathyroid gland is approximately the size of a grain of rice, measuring around 6-8mm in diameter. They have a yellowish-brown color and a lobulated appearance. The structure of the parathyroid gland is composed of two main types of cells:

1. Chief cells: These cells are responsible for secreting parathyroid hormone (PTH), which is the primary function of the parathyroid glands. PTH plays a vital role in regulating calcium and phosphorus levels in the body.

2. Oxyphil cells: These cells are larger and less common than chief cells. Their exact function is not fully understood, but they are believed to have a role in calcium metabolism.

Blood Supply and Innervation

The blood supply to the parathyroid glands is derived primarily from the inferior thyroid artery. The superior parathyroid glands receive their blood supply from the superior thyroid artery, while the inferior parathyroid glands are mainly supplied by the inferior thyroid artery.

In terms of innervation, the parathyroid glands are predominantly supplied by branches of the autonomic nervous system, specifically the sympathetic and parasympathetic fibers.

Function of the Parathyroid Glands

The main function of the parathyroid glands is to secrete parathyroid hormone (PTH). PTH acts on several target tissues to regulate calcium and phosphorus levels in the body. The primary actions of PTH include:

1. Increase in serum calcium levels by stimulating bone resorption, which releases calcium into the bloodstream.
2. Enhancement of calcium absorption in the intestines by activating vitamin D.
3. Reduction of urinary calcium excretion by increasing reabsorption in the kidneys.
4. Stimulation of kidney production of active vitamin D, which aids in calcium absorption.

Clinical Significance

Understanding the anatomy of the parathyroid glands is crucial for diagnosing and treating related disorders. Some common conditions associated with the parathyroid glands include:

1. Hyperparathyroidism: Characterized by excessive secretion of PTH, leading to hypercalcemia and increased bone resorption. This condition can cause kidney stones, bone pain, and muscle weakness.

2. Hypoparathyroidism: Occurs when the parathyroid glands produce insufficient PTH. This condition leads to hypocalcemia, resulting in muscle cramps, seizures, and other neurological symptoms.

3. Parathyroid adenoma: A benign tumor that forms in one of the parathyroid glands, causing excessive PTH secretion. This can result in hypercalcemia and related symptoms.

4. Parathyroidectomy: Surgical removal of the parathyroid glands, often performed to treat hyperparathyroidism or parathyroid adenoma.

In conclusion, the parathyroid glands are small but essential structures that regulate calcium and phosphorus balance in the body. Understanding their anatomy, structure, and function is crucial for the diagnosis and management of related disorders.