Dr.F.Iranmanesh. Calcium,Physiologic chemistry Distribution: 5 th most common element Most prevalent...
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- Slide 1
- Dr.F.Iranmanesh
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- Calcium,Physiologic chemistry Distribution: 5 th most common
element Most prevalent cation in the body Healthy adult contain
1-1.3kg of calcim,99% in the form of hydroxyapatite,1% in ECF &
Soft tissue Serum(Plasma) calcium exists in three forms:
1:Free(Ionized) #50% 2:Complex with anions #10% 3:Bound to plasma
proteins#40%,Mostly Albumin,80%
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- 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]
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- Calcium Function mineralization Blood coagulation Neural
transmission Maintenance of normal tone and excitabilityof Skeletal
and cardiac muscle. Glandular synthesis and regulation of exocrine
& endocrine glands. Preservation of cell membrane integrity and
permeability.
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- Calcium intake Average dietary Intake : 600-800mg/Day
Recommended 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.
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- Absorption enhanced by Growth hormone,acid medium,incresed
protein intake. Decreased with:Ca/phos ratio >2 Phytic
acid,Oxalate,Fatty acids,Cortisol, Excessive alkalinity of
intestinal contents.
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- Ca Excretion Sweath:15-100mg/day Major loss:Urine 100-200mg/day
Wide variation in intake has little effect on U.Excretion Enhanced
by: Acidosis,hypercalcemia,phosphate deprivation and
glucocorticoids. Decresedby PTH,Diuretics,VitaminD
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- Kidney Parathyroid Liver Thyroid c cells Intestine Hypocalemi a
PTH 255255 Hyper ca Phosphorus Urine PT H Ca++ 25-OH-D3 1,25(OH)2D3
Ca++ 1,25(OH)2D3 Calcitonin Calcium Homeostasis
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- Analytical techniques : Total Calcium Clark and collip method
Today 3 methods: 1)Colorimetric analysis 2)Atomic absorption
spectrometry(AAS) 3)Indirect Potentiometry
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- 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 650nm High specificity at slightly acidic PH
Hemolysis,lipemia,icterus,paraproteins and Mg intrfere with
colorimetric methods.
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- Calcein forms fluorescent complex Stimulates at 490nm &
emits at 590nm Titration of complex with EDTA AAS is the reference
method Dilution 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.
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- Analytical techniques Ionized calcium Ion 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.
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- Reference intervals Total calcium Total ca. in adults
8.8-10.3mg/dl(2.20-2.58mmol/L) Serum is the preferred Specimen
Heparinized 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=4.4
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- Reference interval Ionized calcium 4.6-5.3mg/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.
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- Reference interval Urinary calcium Varies with diet Average
300mg/day Urine collection with appropriate acidification to
prevent calcium salt precipitation.(15 ml hydrochloric acid)
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- Phosphorus Physiologic chemistry Adult body content :700mg 85%
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.
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- Function Skeleton Intra & extracellular role. Nucleic
acid,phospholipid,phosphoproteins ATP and NADP.In various enzyme
systems(Adenylate cyclase) Essential for normal muscle
contractility,Neurologic function,Electrolyte transport and oxygen
carrying by Hb.
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- Phosphorus homeostasis Present 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)2D3 Freely 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.
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- 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.
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- Analytical techniques Reaction 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) interfere Prolonged storage
with cells at room temperature causes Ph. Hemolyzed specimens are
Unacceptable (RBC organic esters hydrolize to inorganic phosphate
during storage.)
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- Disorders of mineral metabolism Hypercalcemia Serum ca is
associated with:
Anorexia,Nausea,vomiting,Constipation,hypotonia,depression,high
voltage T waves on ECG,lethargy,coma Persistent hyperca. Causes
ectopic deposition of ca(vessels,connective tissue ad
joints,gastric mucosa,kidney) Most common causes:Primary
hyperpara,Malignancy Others :Renal Failure,Diuretics,Endocrine
disorderes,Vitamin A and D intoxication,Lithium therapy,Milk alkali
synd.,immobilization,Hyperthyroidism,familial hypercalciuric
hypercalcemia.
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- 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 USA F/M : 2/1 Majority
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.
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- Hyperparathyroidism PHPT:Sporadic MEN1 (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
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- 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,others Osteoclast activating
factor,tumor necrosis factor,IL1 Without B.M:Humoral hypercalcemia
of malignancy; Renal,hepatic,epidermoid of head,neck,lung and ilet
cell of pancreasPTH-rP Urinary CAMP excretion + or normal PTH
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- Vitamin D intoxication Granulomatous 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 phosphorus Alkaline
phospatase,Albumin,PTH,PTH-rP,Urine CAMP VitaminD,cortisol,GH,
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- Magnesium 4th most abundant cation in the body(after Na,K,Ca) 2
nd 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)
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- Function,Mg Essential 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 arrythmia
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- Mg GI absorption,Renal Excretion MG:diatery intake:300-350
mg/day Sturable transport system and passive diffusion Renal
excretion:120-140 mg/24hour Thick ascending loop of henle(60-70%)
Distal tubule(10%),Major regulation site. Mg2+ the most important
regulator.(PTH,Calcitonin,glucagon,)
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- Analytical techniques Serum 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.
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- Reference interval,Mg Total 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/dl Ionized Mg:0.44-0.60 mmol/L
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- Thank you for your attention