calcium met 3

8/7/2019 calcium met 3

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MODERATORS

PROF DEEPAK RAI

DR MAHESHA K

PRESENTER: DR NABEEL SHAMS


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INTRODUCTION


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` Calcium -most abundant mineral in the human

body.

` 1.5%- total body weight.

` Along with phosphorous it forms the principal

contituents of the bone.

` Normal serum level 9-11mg/dl


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` Calcium is an divalent cation with multiple roles in

vertebrate physiology

` They can be grouped as either structural or

metabolic


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1.Dietary source` Whole milk 10%

` Low fat milk 18%

` Cheese 27%

` Other dairy products 17%

` Vegetables 7%(Spinach, Turnip, Cabbage, Soya beans)

2. From bones- Resorption`


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`DISTRIBUTION OF CALCIUM


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` 1) calcium in plasma

` 2) calcium in bones


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`

` About 41% combined - plasma proteins

nondiffusible form

` About 9% combined- anionic substances of theplasma and interstitial fluids (citrate and phosphate,

for instance)

` Remaining 50%- both diffusible through the

capillary membrane and ionized


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` The ionised calcium concentration in serum is

approximately 5mg/dl.

` It is the ionised fraction that is biologically activeand is closely regulated


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i) Rapidly exchangeable calcium

ii) slowly exchangeable calcium


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` i) The rapidly exchangeable calcium- maintains

the plasma calcium level

ii) The slowly exchangeable calcium-

bone remodelling


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MEN 400 mg

WOMEN 400mg

PREGNANT WOMEN 1000mg


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` ABSORBTION AND EXCRETION


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` Calcium ions-poorly absorbed from the intestines

` Vitamin D promotes calcium absorption from the

intestines

` Majority of absorbtion takes place from the 1st and

2nd psrt of deudenum


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About 35% of injested calcium is usually

absorbed and the remaining is excreted in faeces

In contrast the absorbtion of phoshate from the

intestines occurs very easilyAbout 10% of the injested calcium is excreted in

urine

98-99% -reabsorbed from renal tubules


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` Majority of reabsorbtion-distal convolutedtubules and proximal part of collecting duct

` The bone contains a type of exchangeablecalcium that is always in equilibrium with calcumions in the extra cellular fluid

The exchangeable calcium provides an bufferingmechanism to maintain the calcium ionconcentration


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Parathormone and Vit D play a major role


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` FACTORS AFFECTNG CALCIUM ABSORBTION


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` Factors causing increased absorbtion

` a) Vit D

` b) PTH

` c) Acidity` d) Amino acids


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Factors causing decreased absorbtion

a)Phytic acid ( present in cereals)

b)Oxalates( leafy vegetables- formation ofinsoluble calcium oxalates)

c) Malabsorbtion syndromes

d) Phosphate: optimum ratio of calcium tophosphorus alowing maximum absorbtion is 1:2 to2:1


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` REGULATION OF THE BLOOD CALCIUM

LEVEL


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` Calcium metabolism is mainly regulated by

` Parathormone

` 1,25 dihydroxycholecalciferol(calcitriol)

` Calcitonin


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` PARATHORMONE


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` Parathhormone secreted by chief cells of the

parathyroid gland

` The pricipal regulator of PTH secretion is the ECFionised calcium concentration

` The regulation of PTH is mediated by calcium

sensing receptor( CASR)


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` Plasma PTH concentrations exhibit diurnal

variation

` They are stable during the afternoon and evening

` They rise around 50% around 2:00 am andsubsequently fall below 50% of the afternoon

values by 9:00am


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` Parathyroid hormone binds to cell surface

receptors in its target tissues

` The two principal target tissues are bone and

kidney where it activates adenylate cyclase and

phospholipase C


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` ACTIONS OF PARATHORMONE


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` On bone

` - stimulates osteoclastic activity hence

enhances the resorption of calcium from the

bones

` Resorption of calcium- two phases

` a) Rapid phase

` b) Slow phase


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` Rapid phase- occurs within minutes

` causes increased permeability of

osteoclasts and osteoblasts for calcium

` Slow phase- Occurs by activation of osteoclasts

` When the osteoclasts get activated they

release proteolytic enzymes and acids leading to

digestion of the organic matrix


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` On kidneys-

` a) Reduces proximal tubular resorbtion of

phosphate

` b) Increases the distal tubular reabsorption of

calcium

` c) Formation of 1,25-dihydroxycholecalciferol from

25-hydroxycholecalciferol


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` On GI tract

`

` PTH increases the absorption indirectly by forming

1,25-dihydrocholecalciferol in the kidneys

` PTH causes activation of Vit D


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` Parathormone-controls extracellular calcium and

phosphate concentrations

` Excess activity- hypercalcemia

` Reduced activity- hypocalcemia

`


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HYPERCALCEMIA


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` 1. Parathyroid related

` a) Primary hyper parathyroidism

` b) Lithium therapy

` c) Familial hpercalciuric calciuria` 2. Malingnancy related

` 3. Vit D realted

` 4. Associated with high bone turnover

` 5. Associated with renal failure

`


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` Mild hypercalcemia often asymptomatic

` Symptoms occur if calcium >12mg/dl

` They include- constipation, polyuria, nausea

vomiting, peptic ulcer desease, weakness,

lethargy


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` Forced calciuresis

` In case of dehydration 0.9% salinerapidly(250ml/hr)

` Bisphosphonates for hypercalcemia of malignancy


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` HYPOCALCIMEA


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` A)Decreased intake or absorption

` B)Increased loss

` C)Endocrine desease

` D)Others


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` Primarily affects the neuromuscular and

cardiovascular systems

` A) Cardiovascular changes:

` Dilatation of the heart

` Prolonged duration of the ST segment and QT

interval` Arrythmias


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` B) Neuromuscular changes:

` Hyper reflexia and convulsions

` Carpopedal spasm` Laryngeal stridor

` Physical findings- Chovstek sign and

Trousseaus sign


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In severe symptomatic hypocalcimea-

10mg/kg of 10% calcium gluconate in one litre

of Dextrose infusion over 4-5 hours

In asymtomatic Hypcalcimea- Oral calcium 1-2gm

and vit d preparations


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` Resorption of calcium from the bones

` Resorption of calcium from the renal tubules

` Absorbtion of calcium from the GI tract


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` CONTROL OF PARATHYROIDSECRETION BY CALCIUM IONS


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` The solid curve shows the acute effect when the

calcium concentration is changed over a period of

a few hours

`

` the calcium ion concentration changes over a

period of many weeks is shown by the dashedline.


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` 1,251,25--DIHYDROXYCHOLECALCIFEROLDIHYDROXYCHOLECALCIFEROL


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` Vitamin D- calcium absorption from the intestinal

tract

` vitamin D must first be converted the final active

product, 1,25-dihydroxycholecalciferol


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` Promotes intestinal calcium absorption

` Promotes phosphate absorption by the intestines

` Decreases renal calcium and phosphate excretion


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` CALCITONIN


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` Secreted by parafollicular in the thyroid gland

` Plasma level of calcitonin is 1-2 mg/dl

` Degraded and excerted by liver and kidney


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` On bones- stimulates osteoblastic activity

` On kidney inhibits the resorption of calcium fromrenal tubules

` On intestine: prevents the absorption of calcium


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` Bone is composed a) organic matrix

b)calcium salts


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` Organic matrix- composed 95% of collagen fibers

and the rest ground substance

` Bone salts are deposited in the organic matrix

which are primarily calcium and phosphate


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` -95% are collagen fibres, They give tensile

strength to the bone

` -The rest is homogenous gelatinous medium

called ground substance


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` COMPOSED PRINCIPALLY OF CALCIUM AND

PHOSPHATE


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` OSTEOBLASTS

` OSTEOCYTES

` OSTEOCLASTS


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` Conversion of cartilage into bone ossification

` Ossification carried out by osteoblasts which laydown the matrix

` Calcium is deposited in the matrix- calcification


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` a) Bone and teeth formation

` b) Neuronal activity

` c) Skeletal muscle activity

`

d) Cardiac activity

` e) Smooth muscle activity

` f) Secretory activity of the glands

` g) Cell division and growth

` h) Coagulation of blood


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