calciumregulation

Calcium regulation, or calcium homeostasis, is the physiological process by which the body maintains stable extracellular and intracellular calcium concentrations. In humans, blood calcium typically remains within a narrow range (about 2.2–2.6 mmol/L for total calcium, with similar free ionized levels), while intracellular calcium serves as a key second messenger in many signaling pathways. Regulation involves the coordinated actions of bone, kidneys, gut, and endocrine signals, with the parathyroid glands playing a central role.

Endocrine regulators include parathyroid hormone (PTH), calcitonin, and active vitamin D (calcitriol). PTH is released in response to low serum calcium and acts to raise calcium by stimulating bone resorption, increasing renal calcium reabsorption, and promoting calcitriol production in the kidney, which enhances intestinal calcium absorption. Calcitonin generally lowers serum calcium by inhibiting osteoclast activity, though its role in adults is modest. Calcitriol increases calcium absorption from the gut and supports bone mineralization. The calcium-sensing receptor (CaSR) on parathyroid and renal cells helps sense circulating calcium and modulates PTH secretion and renal calcium handling.

Organ-level dynamics involve bone as the primary reservoir, with osteoclasts resorbing and osteoblasts forming bone tissue in response to hormonal signals. The kidneys regulate calcium filtration and reabsorption, adjusting urinary calcium loss. The gut absorbs dietary calcium, a process enhanced by calcitriol. Intracellularly, calcium is tightly buffered and maintained by pumps and exchangers such as SERCA in the endoplasmic reticulum, plasma membrane Ca2+-ATPases, and the sodium–calcium exchanger, enabling calcium signaling while preventing cytotoxic overload.

Clinical aspects cover disorders of calcium balance, including hypocalcemia and hypercalcemia, with etiologies such as hypoparathyroidism, hyperparathyroidism, vitamin D deficiency, and chronic kidney disease, and related treatments.