Mineral and bone metabolism - PowerPoint Presentation

Slide1

Mineral and bone metabolism

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%

Slide4

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

]=ĸ

Hostings

&Mclean 1939

[Ca++]=ĸ[pr--]/[

Capr

]

Slide5

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.

Slide6

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.

Slide8

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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ECF

Kidney

Parathyroid

Bone

Liver

Thyroid c cells

Intestine

Hypocalemia

PTH

255

Hyper ca

Phosphorus

Urine

PTH

Ca++

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.

Slide15

Analytical techniquesIonized 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.

Slide16

Reference intervalsTotal 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 intervalIonized 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 4⁰C 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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PhosphorusPhysiologic 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 metabolismHypercalcemia

↑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

.

Slide26

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

½ 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 pancreas…PTH-

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