Parathyroid hormone in the context of "Calcium in biology"

Parathyroid glands are small endocrine glands in the neck of humans and other tetrapods. Humans usually have four parathyroid glands, located on the back of the thyroid gland in variable locations. The parathyroid gland produces and secretes parathyroid hormone in response to low blood calcium, which plays a key role in regulating the amount of calcium in the blood and within the bones.

Parathyroid glands share a similar blood supply, venous drainage, and lymphatic drainage to the thyroid glands. Parathyroid glands are derived from the epithelial lining of the third and fourth pharyngeal pouches, with the superior glands arising from the fourth pouch and the inferior glands arising from the higher third pouch. The relative position of the inferior and superior glands, which are named according to their final location, changes because of the migration of embryological tissues.

The calcium-sensing receptor (CaSR) is a Class C G-protein coupled receptor which senses extracellular levels of calcium ions. It is primarily expressed in the parathyroid gland, the renal tubules of the kidney, pancreatic islets and the brain. In the parathyroid gland, it controls calcium homeostasis by regulating the release of parathyroid hormone (PTH). In the kidney, it has an inhibitory effect on the re-absorption of calcium, potassium, sodium, and water depending on which segment of the tubule is being activated. CaSR has regulatory role in insulin secretion, adhesion and beta-cell proliferation in pancreatic islets.

Since the initial review of CaSR, there has been in-depth analysis of its role related to parathyroid disease and other roles related to tissues and organs in the body. 1993, Brown et al. isolated a clone named BoPCaR (bovine parathyroid calcium receptor) which replicated the effect when introduced to polyvalent cations. Because of this, the ability to clone full-length CaSRs from mammals were performed.

Primary hyperparathyroidism (or PHPT) is a medical condition where the parathyroid gland (or a benign tumor within it) produce excess amounts of parathyroid hormone (PTH). The symptoms of the condition relate to the resulting elevated serum calcium (hypercalcemia), which can cause digestive symptoms, kidney stones, psychiatric abnormalities, and bone disease.

The diagnosis is initially made on blood tests; an elevated level of calcium together with a raised (or inappropriately high) level of parathyroid hormone are typically found. To identify the source of the excessive hormone secretion, medical imaging may be performed. Parathyroidectomy, the surgical removal of one or more parathyroid glands, may be required to control symptoms.

Sarcoidosis, also known as Besnier–Boeck–Schaumann disease, is a non-infectious granulomatous disease involving abnormal collections of inflammatory cells that form lumps known as granulomata. The disease usually begins in the lungs, skin, or lymph nodes. Less commonly affected are the eyes, liver, heart, and brain, though any organ can be affected. The signs and symptoms depend on the organ involved. Often, no symptoms or only mild symptoms are seen. When it affects the lungs, wheezing, coughing, shortness of breath, or chest pain may occur. Some may have Löfgren syndrome, with fever, enlarged hilar lymph nodes, arthritis, and a rash known as erythema nodosum.

The cause of sarcoidosis is unknown. Some believe it may be due to an immune reaction to a trigger such as an infection or chemicals in those who are genetically predisposed. Those with affected family members are at greater risk. Diagnosis is partly based on signs and symptoms, which may be supported by biopsy. Findings that make it likely include large lymph nodes at the root of the lung on both sides, high blood calcium with a normal parathyroid hormone level, or elevated levels of angiotensin-converting enzyme in the blood. The diagnosis should be made only after excluding other possible causes of similar symptoms such as tuberculosis.