The parathyroid glands are small endocrine glands that maintain the body’s internal balance. They continuously monitor and adjust critical mineral levels within the bloodstream, ensuring proper function of various bodily systems.
Anatomical Home of the Parathyroid Glands
The parathyroid glands are typically situated in the neck, specifically positioned behind the thyroid gland. Most individuals possess four of these glands: two superior parathyroid glands and two inferior parathyroid glands. However, variations in number are common, with some people having as few as three or as many as six or more.
Each parathyroid gland is small, often compared to the size of a grain of rice or a pea. They typically measure about 6 millimeters in length, 3 to 4 millimeters in width, and 1 to 2 millimeters in thickness, presenting as yellowish-brown, flat ovoid structures. Despite their close physical proximity and similar names, the parathyroid glands are functionally distinct from the larger thyroid gland, each producing different hormones with specific roles.
While most parathyroid glands are found nestled behind the thyroid, their exact placement can vary. In some cases, they may be located along the esophagus in the neck or even within the chest, particularly in the mediastinum or thymus. These are referred to as ectopic parathyroid glands and occur in about 16% of people.
The Critical Role of Parathyroid Glands
The primary function of the parathyroid glands is to precisely regulate the levels of calcium and phosphate in the blood and bones. They achieve this by producing and releasing parathyroid hormone (PTH) in response to even slight drops in blood calcium. This hormone orchestrates responses across different organ systems to restore mineral balance.
Once released, PTH influences calcium levels through several mechanisms. It stimulates the release of stored calcium from bones into the bloodstream, primarily by indirectly activating bone-resorbing cells. Simultaneously, PTH instructs the kidneys to reabsorb more calcium back into the blood, reducing its excretion in urine, while also promoting the excretion of phosphate. Additionally, PTH stimulates the kidneys to convert vitamin D into its active form, which is essential for the intestines to absorb calcium from consumed food.
Maintaining appropriate calcium levels is important for numerous bodily processes. Calcium facilitates nerve signal transmission and enables muscle contraction, including the beating of the heart. It also plays a role in blood clotting and is essential for building and maintaining strong bones and teeth, where 99% of the body’s calcium is stored.
When Parathyroid Glands Malfunction
When the parathyroid glands do not function correctly, it can lead to imbalances in calcium and phosphate levels, impacting various body systems. One common condition is hyperparathyroidism, where one or more glands become overactive and produce too much PTH. This excess PTH causes blood calcium levels to rise, a condition known as hypercalcemia.
Conversely, hypoparathyroidism occurs when the parathyroid glands produce insufficient amounts of PTH. This results in abnormally low blood calcium levels and often elevated phosphate levels. Both hyperparathyroidism and hypoparathyroidism can disrupt the body’s mineral homeostasis.