The parathyroid glands are small endocrine glands, typically four in number, located in the neck, usually positioned behind the thyroid gland. Despite their small size, these glands perform a significant function within the body. Their primary role involves maintaining a delicate balance of specific minerals, which is fundamental for numerous bodily processes.
What is Parathyroid Hormone?
Parathyroid Hormone (PTH) is a peptide hormone produced and released by the parathyroid glands. Its main job is to maintain balanced levels of calcium, and to a lesser extent, phosphorus and vitamin D, in the bloodstream. The body relies on stable calcium concentrations for proper nerve and muscle function, as well as for strong bones. When calcium levels in the blood drop, PTH is released to restore them to their normal range.
How PTH Regulates Calcium and Phosphate
PTH exerts its effects on several organs to regulate calcium and phosphate levels. It directly influences bones and kidneys, and indirectly impacts the small intestine through its role in vitamin D activation.
In the bones, PTH signals the release of stored calcium into the bloodstream. It achieves this by indirectly stimulating osteoclasts, which are cells responsible for breaking down bone tissue. While PTH binds to receptors on osteoblasts, the cells that build bone, it ultimately promotes the release of a signaling molecule called RANKL. This molecule then binds to osteoclast precursors, leading to the formation of mature osteoclasts that resorb bone and release calcium.
The kidneys are another key target for PTH. Here, PTH increases the reabsorption of calcium back into the bloodstream, preventing its loss in urine. Simultaneously, PTH works to decrease the reabsorption of phosphate, leading to increased phosphate excretion in the urine. This dual action helps to maintain the proper ratio of calcium to phosphate in the blood.
Beyond its direct actions, PTH also plays a role in activating vitamin D. In the kidneys, PTH stimulates the production of an enzyme called 1-alpha-hydroxylase. This enzyme is responsible for converting an inactive form of vitamin D into its biologically active form, calcitriol. Once activated, vitamin D then acts on the small intestine, promoting the absorption of calcium from digested food into the bloodstream.
Health Implications of PTH Imbalances
When the parathyroid glands produce too much or too little PTH, it can lead to health problems due to mineral imbalances. Both high and low PTH levels disrupt the body’s ability to maintain proper calcium and phosphate concentrations.
Hyperparathyroidism occurs when the parathyroid glands produce an excess of PTH, leading to abnormally high calcium levels in the blood, a condition known as hypercalcemia. This overactivity can be caused by a benign tumor in one of the glands or, less commonly, by enlargement of multiple glands. Common symptoms include weakened bones prone to fractures, kidney stones, and fatigue or weakness. Individuals may also experience increased thirst and urination, abdominal discomfort, or difficulties with concentration and memory.
Conversely, hypoparathyroidism is a rare condition where the parathyroid glands do not produce enough PTH, resulting in low blood calcium levels and often elevated phosphate levels. This can occur if the glands are accidentally damaged during neck or thyroid surgery. Symptoms frequently include tingling or burning sensations in the fingers, toes, and lips, as well as muscle aches, cramps, or spasms, particularly in the face, hands, and feet. In more severe cases, individuals might experience seizures or an irregular heartbeat.