<prompt> Organs involved in calcium homeostasis are all exceptLungsKidneysSkinIntestines  <response>: Answer: a Lungs.CALCIUM METABOLISM Total body calcium-lkilogram of which 99 is in bones. Normal serum calcium: 5mEqL or 2.5mmolL or simply 9-10.5 mgdl. Normal dietary requirement: 0.5 to lg.Types of calcium: Ionized calcium 4.5mgdl is responsible for many functions such as muscular contraction, coagulation etc... Maximum calcium absorption occurs in duodenum proximal jejunum, facilitated by gastric acidDiffusibieultra filterable 5.5mgdlNon-diffusibleprotein bound 4.5mgdlIonized calcium 4.5mgdlAlbumin bound4mgdlComplexed with other minerals 0.5mgdlGlobulin bound0.5mgdl Absorption fed by-Acidic pH, hypocalcaemia, proteins Absorption ped by Achlorhydria, phosphates, oxalates, alkalis, hypercalcemia.PARATHYROID HORMONESynthesized by principal chief cells of parathyroid gland. In bone, PTH receptors are located on osteoblasts but not on osteoclasts. Initially and briefly, PTH causes an increase in bone formation by a direct action on osteoblasts. This brief action is the basis for the usefulness of intermittent PTH administration in the treatment of osteoporosis In a second, long-lasting action on osteoclasts, PTH causes an increase in bone resorption. This second action on osteoclasts is indirect mediated by cytokines released from osteoblasts. Thus, osteoblasts, are required for the bone-resorbing action of PTH on osteoclastsSYNTHESIS OF VITAMIN-D 1, 25-dihydroxyvitamin D rapidly induces absorption of Ca by the duodenum transcaltachiaCALCITONIN The Para follicular cells C cells of the thyroid gland secrete Calcitonin. Its secretion is increased by hypercalcemia, hypergastrinemia, and b adrenergic agonists Salmon Calcitonin: produced by ultimo bronchial bodies, is more effective than Calcitonin. Receptors for calcitonin are found in bones and the kidneys. Calcitonin lowers circulating calcium and phosphate levels. It exerts its calcium-lowering effect by inhibiting bone resorption. This action is direct, and calcitonin inhibits the activity of Osteoclasts in vitro. It also increases Ca2 excretion in the urine.FEATURESPTHVITAMIN-DCALCITONINStimulus for releasesb serum ca2 serum ca2 serum P PTH serum ca2Receptor locationOsteoblastOsteoblastOsteoclast Action on: Bone resorption resorption resorptionKidney P reabsorption ca2 reabsorption in distal tubule P reabsorption ca2 reabsorption Intestine ca2 absorption by activation of vit-D P absorption ca2 absorption Overall effect on: Serum calcium Serum phosphorus Other hormones involved in calcium metabolism: Gluco corticoid excess: 4 serum ca2 and leads to osteoporosis. Growth hormone: urinary ca2 excretion Oestrogens testosterone - Prevent osteoporosis. 