Parathyroid hormone

Parathyroid hormone (PTH) is a peptide hormone secreted by the parathyroid glands when blood calcium falls. It raises blood calcium and generally lowers blood phosphate through actions on bone, kidneys, and vitamin D metabolism.

Calcium homeostasis: The regulation of calcium concentrations in blood and tissues within ranges needed for normal function. PTH is one of the principal hormones that corrects falling blood calcium.
Parathyroid glands: Small endocrine glands, usually four, located behind the thyroid gland and responsible for secreting PTH. They are the source of circulating PTH.
Primary hyperparathyroidism: A disorder in which one or more parathyroid glands autonomously secrete excessive PTH. It demonstrates the effects of persistently elevated PTH on calcium and bone.
Calcitonin: A hormone secreted mainly by thyroid C cells that can lower blood calcium by inhibiting osteoclast activity. It often opposes PTH's effects on blood calcium, though its role in adult humans is limited.
Calcium-sensing receptor: A cell-surface receptor that detects extracellular calcium and adjusts hormone secretion and other cellular responses. Parathyroid cells use it to sense blood calcium and tune PTH release.
Calcium: A chemical element essential to bones, muscle contraction, nerve signaling, and many cellular processes. PTH secretion is chiefly regulated by the concentration of ionized calcium in blood.
Hypoparathyroidism: A condition of insufficient PTH secretion or action, typically causing low blood calcium and high phosphate. Its mineral pattern contrasts with excess PTH.
Parathyroid hormone-related protein: A protein that shares structural similarity with PTH and can activate the same principal receptor. It resembles PTH but has distinct normal roles and can cause humoral hypercalcemia of malignancy.
Parathyroid hormone receptor 1: A G-protein-coupled receptor for parathyroid hormone and parathyroid hormone-related protein. It mediates many PTH effects in kidney and bone cells.
Phosphate: A phosphorus-containing ion used in biological molecules, energy transfer, and mineralized tissues. PTH controls its blood level largely by changing kidney excretion.

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