- The parathyroid glands are small, oval-shaped endocrine glands located in the neck, typically positioned on the posterior surface of the thyroid gland.
- Most people have four parathyroid glands, although the number can vary from two to six.
- Despite their close anatomical relationship with the thyroid, the parathyroid glands are functionally and developmentally distinct. Their primary role is to regulate calcium and phosphate homeostasis in the body through the secretion of parathyroid hormone (PTH).
- Parathyroid hormone is a polypeptide hormone that plays a crucial role in maintaining stable levels of calcium in the bloodstream, which is vital for numerous physiological processes including muscle contraction, nerve conduction, blood clotting, and bone health. The secretion of PTH is tightly controlled by the serum calcium concentration through a negative feedback mechanism. When blood calcium levels drop, the parathyroid glands increase PTH secretion; conversely, when calcium levels are high, PTH release is suppressed.
- PTH exerts its effects on three primary target tissues: bone, kidneys, and intestines. In the bones, PTH stimulates osteoclast activity, leading to the resorption of bone matrix and release of calcium into the bloodstream. In the kidneys, PTH enhances calcium reabsorption in the distal tubules and decreases phosphate reabsorption, thereby preventing calcium loss in the urine while promoting phosphate excretion. Additionally, PTH stimulates the conversion of 25-hydroxyvitamin D into its active form, calcitriol (1,25-dihydroxyvitamin D3), in the kidneys. Calcitriol, in turn, increases intestinal absorption of calcium and phosphate, further contributing to calcium balance.
- The proper functioning of the parathyroid glands is critical for maintaining calcium homeostasis. Hypoparathyroidism, a condition characterized by insufficient PTH production, leads to hypocalcemia, which can cause muscle cramps, tetany, seizures, and cardiac abnormalities. Causes may include surgical removal or damage to the parathyroid glands during thyroid surgery, autoimmune disorders, or genetic conditions. Treatment often involves calcium supplements and active forms of vitamin D.
- On the other hand, hyperparathyroidism results from excessive production of PTH and is classified as primary, secondary, or tertiary. Primary hyperparathyroidism is usually caused by a parathyroid adenoma (a benign tumor) or, less commonly, hyperplasia or carcinoma. It leads to hypercalcemia, which may present with symptoms such as kidney stones, bone pain, abdominal discomfort, and neuropsychiatric disturbances. Secondary hyperparathyroidism often develops in response to chronic kidney disease or vitamin D deficiency, while tertiary hyperparathyroidism may occur after long-standing secondary hyperparathyroidism, particularly in patients on dialysis.
- Diagnosis of parathyroid disorders involves measuring serum calcium, PTH, phosphate, and vitamin D levels. Imaging studies such as ultrasound, sestamibi scans, or CT scans can help localize abnormal parathyroid tissue in cases requiring surgical intervention.
