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Download MBBS Calcium and Phosphate Lecture PPT

Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Calcium and Phosphate Lecture PPT

This post was last modified on 30 November 2021




Calcium in body(1100-1200gm)

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Plasma(1%);

Bones

range : 9-

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(99%)

11mg/dL

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Diffusible

Stable pool(99%) Readily (59%)

Non-diffusible

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(41%): bound

exchangeable

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to albumin

pool(1%)

? Facts to keep in mind:-normal plasma level of

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calcium is 9-10.5mg/dl(5mEq/L,2.5mmol/L)

? Free, ionized calcium (Ca2+) is important for blood

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coagulation, muscle contraction and neuronal

function

? Extent of calcium binding to plasma protein

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levels of plasma proteins

? What is the effects of acid-base disturbances

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on plasma protein-binding of Ca 2+ and the

ionized Ca 2+ concentration in blood?
Absorption of calcium in GIT

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? TRPV6 channels----> responsible for calcium

absorption in intestine

? Absorbed calcium sequestered by calbindin-D

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? Enters the blood stream via sodium calcium

exchanger/ calcium dependent ATPase TRPV6

channels----> responsible for calcium absorption

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in intestine

? Absorbed calcium sequestered by calbindin-D
? Enters the blood stream via sodium calcium

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exchanger/ calcium dependent ATPase
Plasma calcium ?filtered by kidneys

98%-99% are reabsorbed (60% from PCT;

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remaining ?ascending loop of Henle and distal

tubule)

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PTH ---- regulates the re-absorption from distal

tubule (regulates the expression of TRPV5

channels)

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Phosphorous

Total : 500-800 gm (plasma level = 2.5-4.5mg%)

80-85% : skeletal

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2/3rd :organic; 1/3rd inorganic (total plasma level = 12mg/dL)

kidney : 85%-90% of filtered Pi reabsorbed (PCT :active

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transport---sodium dependent Pi cotransport )

Na- Pi IIa and Na- Pi IIc

Na-Pi II a ----> powerfully inhibited by PTH

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GIT : Pi absorbed in duodenum & other parts of

small intestine (Na-Pi IIb)

Excretion : ed : high phosphate diet,

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hyperparathyroidism

ed : low phosphate diet,

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hypoparathyroidism
Physiological effects of altered calcium levels:-

Hypocalcemia :-

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?ed neuronal excitability
? tetany (calcium level about 6.4mg/dL)
? seizures

?Features of hypocalcemic tetany

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?Chvostek's sign
?Trousseau's sign
?carpopedal spasm
?laryngospasm

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Hypercalcemia (>12mg/dL)

?Depresses nervous system
?Sluggish reflex

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?Muscle activity depressed
?Lack of appetite
?Constipation

List various functions of calcium and phosphate

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Physiology of Bone
?Bone is a living tissue
?It is a specialized connective tissue
?Compact bone -30% matrix(framework)

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& 70% salts
?Organic matrix :90-95% collagen fibers,mainly type1

&Groundsubstance (ECF+Proteoglycans).
?Bone salts:Hydroxypatites{Ca10(PO4)(OH)2}

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Compact /cortical bone Trabecular/Spongy bone
?80%

?20%

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?Forms outer layer of bone. ?Inside the cortical bone
?Surface to volume ratio low ?Surface to volume ratio high
?Nutrients provided by

?Nutrients diffuse from ECF

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Haversian canal.

Bone formation

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? During fetal development bone formation

occurs by:

Enchondral bone Intramembranous bone

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formation(majority) formation e.g.; clavicle,
mandible, certain bones of
skull.

Bone formation by osteoblasts

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?Osteoid formation (95% collagen+5% proteoglycan) by

osteoblasts.
?Osteoid is secreated towards the interior of bone.
?Precipitation of calcium and phosphate on surface of

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collagen (mineralization)
?Formation of hydroxyapatite , Ca10 (PO4)6(OH)2,

crystals (Ca:P:: 1.3-2)

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Magnesium, sodium, potassium, and carbonate ions are also

present among the bone salts
? Collagen :tensile strength;

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? hydroxypatite : compressional strength
?Deposition and absorption of bone--remodeling of

bone
?Bone deposition and absorption are normally in

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equilibrium.
?Continual physical stress stimulates osteoblastic

deposition and calcification of bone.

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Bone Remodelling

Bone deposition & Bone resorption.

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Requires 3 types of cells.
?Osteoblasts: secrete extracellular organic matrix

within which calcium phosphate crystal precipitate.
?Osteocyte: Retired osteoblast imprisoned within

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bony wall around them.
?Osteoclasts: Resorb bone by secreting acids &

enzymes.They are cells of mononuclear phygocytic

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system.
Mechanism of bone resorbtion

? Osteoclasts attaches to the part of bone

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to be reabsorbed by integrins .

Forms "sealing zone"

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? Proton pump(H+ dependent ATPases)migrate

From endosomes to the cell membrane.

Ph to 4 in this zone

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Contd.

? The acidic pH dissolves hydroxypatite,

And proteases breakdown collagen.

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Ca, P,and collagen breakdown products are

released into the interstitial fluid.

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?Hydroxyproline is an index of bone resorbtion.

Factors controlling bone formationand

resorbtion

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? GH, IGF, insulin, estrogen, testosterone, vit D ,

calcitonin, PDGF, Stimulates bone

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formation.

? Cortisol inhibits bone formation.
? Parathormone, cortisol,thyroxine,PGs,IL-1&6,
TNF, Stimulates bone resorbtion.

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?Despite supersaturation of calcium and phosphorus ions in

ECF hydroxypatite crystals fail to precipitate in other

tissues........... Why?

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?Osteoid? Osteocytes?
?Mechanism of bone absorption by osteoclasts?
?The importance of exchangeble calcium ion in bone?

Physiological importance of continued deposition and

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absorption of bone?
?Continual physical stress stimulates osteoblastic

deposition and calcification of bone....... How?

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?Factors that control bone formation and resorption?
Applied physiology

? Osteoporosis : decrease in bone mass and

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density.

? Involutional osteoporosis

?Postmenopausal osteoporosis

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? Causes:Hyperparathyroidism,Hyperthyroidism,

Cushing's syndrome ,vit c ,alcoholism,etc.

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? Treatment: Administeration of vit D and

calcium tablets.
Contd.

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Osteopetrosis
? There is defective increase in bone formation.
? Rare & often severe disease.
? Osteoclasts are defective, unable to resorb

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bone in usual fashion so osteoblasts operate

unopposed.

? Neurological and hematological abnormalities.

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