USMLE Guide: Parathyroid

Introduction

The parathyroid glands are four small, pea-sized glands located in the neck, behind the thyroid gland. They play a crucial role in maintaining calcium and phosphorus levels in the body and are involved in the regulation of bone metabolism. Understanding the anatomy, function, and disorders of the parathyroid glands is essential for medical students preparing for the USMLE exams. This guide aims to provide a comprehensive overview of the parathyroid glands, focusing on their anatomy, physiology, and common disorders.

Anatomy

• The parathyroid glands consist of four small, oval-shaped glands.
• Usually, two are located on each side of the thyroid gland, with the superior glands being closer to the thyroid gland and the inferior glands being closer to the thymus gland.
• Each gland is approximately 5 mm in diameter and weighs around 30-40 mg.

Physiology

• The parathyroid glands secrete parathyroid hormone (PTH), which plays a vital role in regulating calcium and phosphorus levels in the body.
• PTH increases blood calcium levels by stimulating the release of calcium from bones, increasing calcium absorption from the intestines, and reducing calcium excretion by the kidneys.
• PTH also promotes the excretion of phosphorus by the kidneys and the activation of vitamin D, which helps in the absorption of calcium from the intestines.

Disorders

Hyperparathyroidism

• Hyperparathyroidism is a condition characterized by excessive secretion of PTH, leading to increased blood calcium levels.
• Primary hyperparathyroidism is most commonly caused by a benign tumor (adenoma) in one of the parathyroid glands.
• Secondary hyperparathyroidism can occur in response to conditions such as chronic kidney disease or vitamin D deficiency.
• Symptoms may include fatigue, bone pain, kidney stones, and gastrointestinal disturbances. Severe cases can lead to osteoporosis, renal failure, or pancreatitis.
• Diagnosis is made by measuring serum calcium and PTH levels, as well as imaging studies such as ultrasound or sestamibi scan.
• Treatment options include surgical removal of the affected parathyroid gland(s) or medication.

Hypoparathyroidism

• Hypoparathyroidism is characterized by insufficient secretion of PTH, resulting in decreased blood calcium levels.
• It can be caused by surgical removal of the parathyroid glands, autoimmune disorders, or genetic conditions.
• Symptoms may include muscle cramps, tingling in the lips and extremities, seizures, and abnormal heart rhythms.
• Diagnosis is made by measuring serum calcium and PTH levels.
• Treatment involves calcium and vitamin D supplementation to maintain normal blood calcium levels.

Parathyroid Adenoma

• Parathyroid adenoma is a benign tumor that develops in one of the parathyroid glands.
• It is the most common cause of primary hyperparathyroidism.
• Symptoms are often related to hypercalcemia and may include fatigue, weakness, bone pain, and kidney stones.
• Diagnosis is made by measuring serum calcium and PTH levels, as well as imaging studies such as ultrasound or sestamibi scan.
• Surgical removal of the adenoma is the preferred treatment.

Conclusion

Understanding the anatomy, physiology, and common disorders of the parathyroid glands is crucial for medical students preparing for the USMLE exams. This guide provides a comprehensive overview of the parathyroid glands, focusing on their anatomy, physiology, and common disorders such as hyperparathyroidism, hypoparathyroidism, and parathyroid adenoma.