Mineral and bone metabolism

Mineral and bone metabolism

Dr.F.Iranmanesh

Calcium,Physiologic chemistryDistribution:5th most common elementMost prevalent cation in the bodyHealthy adult contain 1-1.3kg of calcim,99% in the form of hydroxyapatite,1% in ECF & Soft tissueSerum(Plasma) calcium exists in three forms: 1:Free(Ionized) #50%2:Complex with anions #10%3:Bound to plasma proteins#40%,Mostly Albumin,80%

Calcium binds to negatively Charged sites of proteins ,so dependent to PH & Protein cncentration.Alkalosis : binding so decreased free ca.Acidosis : Binding so Increased free ca.[Ca++][pr--]/[Capr]= Hostings &Mclean 1939[Ca++]=[pr--]/[Capr]4Calcium FunctionmineralizationBlood coagulationNeural transmissionMaintenance of normal tone and excitabilityofSkeletal and cardiac muscle.Glandular synthesis and regulation of exocrine & endocrine glands.Preservation of cell membrane integrity and permeability.Calcium intakeAverage dietary Intake : 600-800mg/DayRecommended 1200 mg during preg.& Lactation and 800-1200 mg during childhood.Ca absorption : Active transport in Duodenum and upper jejunum.(50%)Increased in pregnancy, lactation and rapid growth and decreased with advanced ages.Major stimulus of ca. absorption is vitamin D.Absorption enhanced by Growth hormone,acid medium,incresed protein intake.Decreased with:Ca/phos ratio >2Phytic acid,Oxalate,Fatty acids,Cortisol,Excessive alkalinity of intestinal contents.

Ca ExcretionSweath:15-100mg/dayMajor loss:Urine 100-200mg/dayWide variation in intake has little effect on U.ExcretionEnhanced by:Acidosis,hypercalcemia,phosphate deprivation and glucocorticoids.Decresedby PTH,Diuretics,VitaminDECFKidneyParathyroidBoneLiverThyroid c cellsIntestineHypocalemiaPTH255Hyper caPhosphorusUrinePTHCa++Ca++25-OH-D31,25(OH)2D3Ca++1,25(OH)2D3CalcitoninCalcium Homeostasis

Analytical techniques :Total CalciumClark and collip methodToday 3 methods:1)Colorimetric analysis 2)Atomic absorption spectrometry(AAS)3)Indirect Potentiometry

Colorimetric Metallochromatic indicators:O-Cresolphthalein complexon(CPC)Red color in alkaline solution.Measured at 580nm.Addition of 8 -hydroxyquinolone:Mg.Arsenazo III ,Ca-indicator complex:Measured at 650nmHigh specificity at slightly acidic PHHemolysis ,lipemia,icterus,paraproteins and Mg intrfere with colorimetric methods.

Calcein forms fluorescent complexStimulates at 490nm & emits at 590nmTitration of complex with EDTAAAS is the reference methodDilution with Lanthanum hydrochloride to reduce viscosity and interference from proteins and organic and inorganic ions.Ind.Potentiometry:An electrode selective for ca.measures a sample that is also measured against a Na selective electrode.Analytical techniquesIonized calciumIon selective electrodes(ISE)Accurate,precise,automatic determination of ionized(Free)Ca.Consists of a membrane separating a reference solution (CaCl2,AgCl)and a reference electrode(Ag/AgCl or calomel) from the solution to be analyzed.

Reference intervalsTotal calciumTotal ca. in adults 8.8-10.3mg/dl(2.20-2.58mmol/L)Serum is the preferred SpecimenHeparinized plasma is also acceptable.Citrate,Oxalate,EDTA interfere with commonly used methods.Hemolysis ,icterus,lipemia,paraproteins and Mg interfere with colorimetric methods.Total ca.corrected for hypoalbuminemia=total ca(measured)+[(Normal Albumin-patient,sAlb.)x0.8]Normal albumin=4.4Reference intervalIonized calcium4.6-5.3mg/dl(1.16-1.32 mmol/L)Whole blood,Heparinized plasma or serum are acceptable.Specimens should be collected anaerbically and transported on ice and stored at 4C to prevent loss of CO2 and glycolysis and stabilize PH.Reference interval Urinary calciumVaries with dietAverage 300mg/dayUrine collection with appropriate acidification to prevent calcium salt precipitation.(15 ml hydrochloric acid)

18PhosphorusPhysiologic chemistry

Adult body content :700mg85% in Skeleton(Inorganic),15% in ECF & soft tissue(Organic)In blood,Plasma(Inorganic) ,cells (Organic)In serum ratio of H2PO4-:HPO4-- is pH dependent.1:1 in acidosis,1:4 in pH 7.4,1:9 in alkalosis.Serum phosphorus 10% bound to proteins,35% complex with Na,calcium;Mg and 55% free.Only inorganic ph.is measured in routine.FunctionSkeletonIntra & extracellular role.Nucleic acid,phospholipid,phosphoproteinsATP and NADP.In various enzyme systems(Adenylate cyclase)Essential for normal muscle contractility,Neurologic function,Electrolyte transport and oxygen carrying by Hb.Phosphorus homeostasisPresent in virtually all foods.Average dietary intake 800- 1400 mg/day.60% -80% of intake is absorbed mainly by passive transport.Active transport stimulated by 1.25(OH)2D3Freely filtered in glomerulus.>80% reabsorbed in proximal tubule and smaller in distal tubule.Proximal transport:(Na-P cotransport)mainly regulated by ph.intake and PTH.PTH inhibits Na-P Cotransport and causes phsphaturia.Reference intervals

Adults:2.8-4.5 mg/dl(0.89-1.44 mmol/L)Higher in growing children(4.0-7.0)Serum phosphate has DIURNAL VARIATION.Higer levels in afternoon and evenings.Best measured in FASTING MORNING.Levels are influenced by dietary intake,meals,and exercise.Analytical techniquesReaction of inorganic phosphate with ammonium molibdate to form phosphomolibdate complex measured at 340 nm in autoanalyzers.Complex can be reduced to form molibdenum blue measured at 600 to 700 nm.Enzymatic methods.Serum is preferred.Most anticoagulants(Except heparin) interfereProlonged storage with cells at room temperature causes Ph.Hemolyzed specimens are Unacceptable (RBC organic esters hydrolize to inorganic phosphate during storage.)

24Disorders of mineral metabolismHypercalcemiaSerum ca is associated with:Anorexia,Nausea,vomiting,Constipation,hypotonia ,depression,high voltage T waves on ECG,lethargy,comaPersistent hyperca. Causes ectopic deposition of ca(vessels,connective tissue ad joints ,gastric mucosa,kidney)Most common causes:Primary hyperpara,MalignancyOthers :Renal Failure,Diuretics,Endocrine disorderes,Vitamin A and D intoxication,Lithium therapy,Milk alkali synd.,immobilization,Hyperthyroidism,familial hypercalciuric hypercalcemia.Primary Hyperparathyroidism(PHPT)PTH in the absence of an appropriate physiologic stimulus causing generalized disorder of Ca,Ph,Bone metabolism.100,000 case/Year in USAF/M : 2/1Majority caused by solitary parathyroid adenoma.Others:Multiple adenoma,Hyperplasia ,Rarely carcinoma.Ca,Phosphate,Mild acidosis(Renal Bicarbonate reabsorption) Ca due to :1)Direct action PTH on Bone,increased resorption.2)PTH activated renal reabsorption 3)PTH stimulated increased renal biosynthesis of 1,25(OH)2D3 which increases intestinal calcium absorption or more are asymptomatic.HyperparathyroidismPHPT:SporadicMEN1 (Pituitary &pancreas tumors,Zollinger Ellison synd.)MEN2A(Pheo. &Medullary CA of thyroid.)Secondary Hyperparathyroidism:Resistance to PTH: RF,VIT D deficincy,Low to normal Ca,High phosphate.Renal osteodistrophy

Malignancy :the most frequent cause of Hpercalcemia in the hospital inpatient population.Malignancy associated hypercalcemia:With and without bony metastasis.With B.M:Hemathologic(Multiple Myeloma,Lymphoma,lukemia)breast,Lung,othersOsteoclast activating factor,tumor necrosis factor,IL1Without B.M:Humoral hypercalcemia of malignancy;Renal,hepatic,epidermoid of head,neck,lung and ilet cell of pancreasPTH-rPUrinary CAMP excretion + or normal PTH

Vitamin D intoxicationGranulomatous disorders(Sarcoidosis)Milk alkali syndrome(Serumca,U.ca,Azotemia,Alkalosis)Lab tests in diff DX of hypercalcemia:Serum total & Ionized ca. ,Urine ca.Serum &urine phosphorusAlkaline phospatase,Albumin,PTH ,PTH-rP,Urine CAMPVitaminD,cortisol,GH,Magnesium4th most abundant cation in the body(after Na,K,Ca)2nd most prevalent intracellular cation.Normal body content:1000mmol (22.66mg)50-60% in Bone,40-50% in soft tissue.1/3 skeletal Mg is exchangeable.Reservoir for extracellular Mg(1% of total body Mg)Serum:55% Ionized(Mg2+),15%complex with phosphate,citrate,,30% protein bound(Albumin)45% of TB Mg, is intracellular.(ATP,Nucleus,mith0chondria;RE)Function,MgEssential for >300 cellular Enzymes.(Transfer of phosphate groups,DNA replication ,transcription,RNA translation,ATP)Cellular energy metabolism,Membrane,nerve conduction,Cardiac muscle(K pump)Mg after cardiac Surgury,causes refractory plasma electrolyte abnormalities(K)and arrythmiaMgGI absorption,Renal ExcretionMG:diatery intake:300-350 mg/daySturable transport system and passive diffusionRenal excretion:120-140 mg/24hourThick ascending loop of henle(60-70%)Distal tubule(10%),Major regulation site.Mg2+ the most important regulator.(PTH,Calcitonin,glucagon,)

Analytical techniquesSerum is preferred over plasma.Anticoagulants interfere.Methods:AAS,Reference method(remove of ph. With lanthanum)Photometric methods,Routine,Metallochromatic indicators(Calmagite:collor in Alk.sol.520nm)Ionized(Free)Mg:ISE(Neutral ionophores selective for Mg2+)Interference with ca.Reference interval,MgTotal Mg:1.7-2.2mg/dl(0.75-0.95 mmol/L)No age or sex difference in total Mg concentration.CSF Mg:2.0-2.7mg/dlIonized Mg:0.44-0.60 mmol/L

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