Organs involved in calcium homeostasis are all except

Answer: a) Lungs.CALCIUM METABOLISM* Total body calcium-lkilogram of which 99% is in bones.* Normal serum calcium: 5mEq/L or 2.5mmol/L or simply 9-10.5 mg/dl.* Normal dietary requirement: 0.5 to lg.Types of calcium:* Ionized calcium (4.5mg/dl) is responsible for many functions such as muscular contraction, coagulation etc...* Maximum calcium absorption occurs in duodenum & proximal jejunum, facilitated by gastric acidDiffusibie/ultra filterable (5.5mg/dl)Non-diffusible/protein bound (4.5mg/dl)Ionized calcium (4.5mg/dl)Albumin bound(4mg/dl)Complexed with other minerals (0.5mg/dl)Globulin bound(0.5mg/dl)* 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 (transcaltachia)CALCITONIN* 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 release|sb serum ca2+| serum ca2+| serum P| PTH| serum ca2+Receptor 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.