The parathyroid glands are small endocrine organs that maintain the body’s internal balance. They are often confused with the nearby thyroid gland, but they perform a distinct and essential function. Their primary role is regulating the levels of calcium, a mineral fundamental to nerve, muscle, and bone health. This constant regulation is necessary for overall physiological stability.
Exact Location and Appearance
Most individuals have four parathyroid glands, situated in the neck on the posterior surface of the thyroid gland. They are two pairs of glands, with a superior and an inferior gland positioned near each of the thyroid’s lobes. Each gland is small, measuring about the size of a grain of rice or a small pea.
These yellowish-brown, flat, ovoid structures are often embedded within the thyroid capsule or surrounding neck tissue. Their small size and close proximity explain why they are sometimes inadvertently affected during thyroid surgery. In a small percentage of people, the glands are found in an ectopic, or abnormal, location, sometimes lower in the neck or even within the chest cavity.
The Role of Parathyroid Hormone
The main product of the parathyroid glands is Parathyroid Hormone (PTH), which serves as the primary regulator of calcium and phosphate concentrations in the blood. The glands monitor blood calcium levels through a calcium-sensing receptor on the surface of their chief cells. When calcium levels drop, PTH secretion increases to restore balance.
The hormone acts on three main target organs to elevate circulating calcium. In the skeletal system, PTH stimulates cells to break down bone tissue, a process called bone resorption, which releases stored calcium into the bloodstream. This mechanism provides a calcium reservoir the body can draw upon as needed.
In the kidneys, PTH has a dual effect: it signals the renal tubules to increase the reabsorption of calcium back into the blood, preventing its loss in the urine. PTH also promotes the excretion of phosphate, which is important because high phosphate levels can interfere with calcium balance. The hormone also stimulates the kidneys to activate a form of Vitamin D.
The activated Vitamin D, known as calcitriol, travels to the small intestine, where it enhances the absorption of calcium from digested food. This coordinated action across the bones, kidneys, and intestines maintains blood calcium within a stable range. Calcium is involved in muscle contraction, nerve signaling, and blood clotting.
Understanding Parathyroid Disorders
Malfunction of the parathyroid glands leads to disorders characterized by an imbalance in blood calcium. Hyperparathyroidism occurs when one or more glands become overactive, producing an excess of PTH. This surplus results in hypercalcemia, or high calcium levels in the blood.
Symptoms of hyperparathyroidism can include fatigue and difficulty concentrating. Sustained high calcium levels can lead to serious complications, such as the formation of kidney stones or the loss of bone density, causing osteoporosis and bone pain.
Conversely, hypoparathyroidism is a condition where the glands produce too little PTH, causing blood calcium levels to fall too low. This condition often occurs after damage to the glands during neck surgery. Low calcium can cause hypocalcemia symptoms, such as numbness and tingling in the fingers, toes, or around the mouth, and more severe symptoms like muscle stiffness and cramping.