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Calcium & phosphate homeostasis

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****vitamin D2 is obtained from exogenous source -which is also known as ergocalciferol not ergosterol ****

Hello everyone welcome to easy med today we are going to discuss about calcium and phosphate homeostasis we study calcium and phosphate together because they are the major constituent of bone and teeth and they are regulated by the same hormones talking about calcium about 99 percent of total body calcium is present in bone about 1 percent in soft tissue and

Less than 0.2 percent is present in serum and normal serum calcium level is 9 to 11 milligram per deciliter this serum calcium exists in three distinct forms aprox 10 percent is complex calcium that is calcium bound to organic and inorganic anion about 40 percent is bound to albumin and remaining 50 percent it circulates as free ionized calcium this free ionized

Calcium involved in most of the biological actions of calcium as action potential formation muscle contraction and others this serum calcium level is regulated within narrow range of 9 to 11 milligram per deciliter now let’s talk about phosphate phosphate is a part of atp molecule and it helps in activation and inactivation of enzyme as well plasma phosphate

Concentration is not strictly regulated and its level fluctuated throughout the day particularly after meal there are three organs and three hormones that govern calcium and phosphate homeostasis parathyroid hormone vitamin d and calcitonin are hormone responsible for it and that acts on organs like kidney intestine and bone parathyroid hormone it’s synthesized

Stored and secreted by cheap cell of part thyroid gland in response to decreased calcium level at normal state extracellular calcium bind to g protein couple receptor present in cell membrane of chip cell and via ip3 and dsg pathway calcium is produced and protein kinase c is activated that inhibits parathyroid hormone synthesis and release so decrease in

Calcium levels stimulates myothyroid hormone secretion before knowing the response of these hormone at organ level let’s talk about paracellular and trans cellular transport paracellular transport first it is carried through interstellar space second it is passive process before paracellular before passive third and most important it is not subject to hormonal

Control trans cellular transport it is carried through cell membrane second it is active process and thought it is subject to hormonal control in kidney calcium is reabsorbed from both roots that is paracellularly and transcenderly para similarly from obesity and ascending loofah family whereas transcellarly from dct and also 80 to 95 percent of phosphate is

Reabsorbed from pct trans cellularly and in intestine both paracellularly and trans cellularly calcium is absorbed external partial hormone in kidney as we discussed earlier only trans cellular transport is subject to hormonal control so there are three major function of parathyroid hormone in kidney first one is it increases calcium reabsorption from dct and

Proximal convoluted tubule by increasing transcription and inhibiting endocytosis of trpv5 at luminal side calcium transporter like trpv5 and 6 is present through which calcium is reabsorbed from renal tubule free calcium can disturb cellular metabolism so it binds to cal binding and at beso lateral side it is transported into serum via sodium calcium exchanger

And calcium pump second pathetic hormone increases phosphate excretion from kidney and thought it increases vitamin d reabsorption external path higher hormone in bone in bone it increases bone resorption and hence increases serum calcium talking about mechanism firstly pathetic hormone binds to g protein copper receptor present on cell membrane of osteoblast

Which increase activity of adenylyl cyclades hence camp level increases so protein kinase c is activated that release rank ligand from osteoblast as osteoclasts have ranked to bind with rank ligand of osteoblast so osteoclastic activity is increased which causes increased bone resorption and result in increased serum calcium levels external path higher hormone

In intestine well parathyroid hormone does not have direct action in intestine but it converts vitamin d into its active form by stimulating one alpha hydroxylation which ultimately increases calcium and phosphate absorption from intestine vitamin d there are two forms of vitamin d in our body d2 that is ergosterol which is obtained from exogenous source like

Plants and the three that is cholecalciferol which is indigenous source and synthesized in skin in presence of uv light then 25 hydroxylation takes place in liver and which converts cholecalciferol into 25 hydroxycola calciferol and finally one alpha hydroxylation takes place in kidney by enzyme one alpha hydroxylase and one comma 25 dihydroxycola calciferol

Is formed which is also known as calcitriol and is the active form of vitamin d action of vitamin d calcitriol or active form of vitamin d has major action in intestine where it increases both calcium and phosphate absorption it has same but weak action in kidney in bone it is essential for both bone formation and mobilization of calcium and phosphate from bone

And coordinates the remodeling action of osteoclasts and osteoblasts talking about mechanism of action of calcitriol calcitra acts like straight hormone it enters the target cell and binds to the cytoplasm receptor and the sperm hormone receptor complex interact with dna and ultimately it increased transcription of calvinine due to increasing availability of cal

Binding calcium absorption increases now calcitonin calcitonin is separated from para follicular shear cell of thyroid gland and it is antagonised to pathogen hormone and this hormone is secreted in response to hypercalcemia it exerts its hypocalcemic action primarily by inhibiting osteoclast mediated bone resorption and secondarily by stimulating renal calcium

Clearance so overall some important points are serum calcium level is regulated within narrow range of 9 to 11 milligram per deciliter kidney intestine and bone are the major organs and parathyroid hormone vitamin d and calcitoine are major hormones responsible for calcium and phosphate homeostasis only trans cellular transport is subject to hormonal control

One comma 25 dihydroxycholical spiral or calcitriol is active form of vitamin d pathogen hormone increases calcium reabsorption and phosphate excretion from kidney it increases osteoclastic activity in bone and his increased calcium serum calcium level and it has not direct action in intestine but it estimate one alpha hydroxylation of vitamin d that ultimately

Increases calcium and phosphate level vitamin d increases both absorption of calcium and phosphate from kidney and intestine at bone it has both osteoblastic and osteoclastic activity calcitonin has hypocalcemic action primarily by decreasing osteoclastic activity and secondarily by calcium clearance from kidney thanks for watching if you have any question

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Calcium & phosphate homeostasis By Easy Med