Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Calcium and Phosphate Lecture PPT
Calcium in body(1100-1200gm)
Plasma(1%);
Bones
range : 9-
(99%)
11mg/dL
Diffusible
Stable pool(99%) Readily (59%)
Non-diffusible
(41%): bound
exchangeable
to albumin
pool(1%)
? Facts to keep in mind:-normal plasma level of
calcium is 9-10.5mg/dl(5mEq/L,2.5mmol/L)
? Free, ionized calcium (Ca2+) is important for blood
coagulation, muscle contraction and neuronal
function
? Extent of calcium binding to plasma protein
levels of plasma proteins
? What is the effects of acid-base disturbances
on plasma protein-binding of Ca 2+ and the
ionized Ca 2+ concentration in blood?
Absorption of calcium in GIT
? TRPV6 channels----> responsible for calcium
absorption in intestine
? Absorbed calcium sequestered by calbindin-D
? Enters the blood stream via sodium calcium
exchanger/ calcium dependent ATPase TRPV6
channels----> responsible for calcium absorption
in intestine
? Absorbed calcium sequestered by calbindin-D
? Enters the blood stream via sodium calcium
exchanger/ calcium dependent ATPase
Plasma calcium ?filtered by kidneys
98%-99% are reabsorbed (60% from PCT;
remaining ?ascending loop of Henle and distal
tubule)
PTH ---- regulates the re-absorption from distal
tubule (regulates the expression of TRPV5
channels)
Phosphorous
Total : 500-800 gm (plasma level = 2.5-4.5mg%)
80-85% : skeletal
2/3rd :organic; 1/3rd inorganic (total plasma level = 12mg/dL)
kidney : 85%-90% of filtered Pi reabsorbed (PCT :active
transport---sodium dependent Pi cotransport )
Na- Pi IIa and Na- Pi IIc
Na-Pi II a ----> powerfully inhibited by PTH
GIT : Pi absorbed in duodenum & other parts of
small intestine (Na-Pi IIb)
Excretion : ed : high phosphate diet,
hyperparathyroidism
ed : low phosphate diet,
hypoparathyroidism
Physiological effects of altered calcium levels:-
Hypocalcemia :-
?ed neuronal excitability
? tetany (calcium level about 6.4mg/dL)
? seizures
?Features of hypocalcemic tetany
?Chvostek's sign
?Trousseau's sign
?carpopedal spasm
?laryngospasm
Hypercalcemia (>12mg/dL)
?Depresses nervous system
?Sluggish reflex
?Muscle activity depressed
?Lack of appetite
?Constipation
List various functions of calcium and phosphate
Physiology of Bone
?Bone is a living tissue
?It is a specialized connective tissue
?Compact bone -30% matrix(framework)
& 70% salts
?Organic matrix :90-95% collagen fibers,mainly type1
&Groundsubstance (ECF+Proteoglycans).
?Bone salts:Hydroxypatites{Ca10(PO4)(OH)2}
Compact /cortical bone Trabecular/Spongy bone
?80%
?20%
?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
Haversian canal.
Bone formation
? During fetal development bone formation
occurs by:
Enchondral bone Intramembranous bone
formation(majority) formation e.g.; clavicle,
mandible, certain bones of
skull.
Bone formation by osteoblasts
?Osteoid formation (95% collagen+5% proteoglycan) by
osteoblasts.
?Osteoid is secreated towards the interior of bone.
?Precipitation of calcium and phosphate on surface of
collagen (mineralization)
?Formation of hydroxyapatite , Ca10 (PO4)6(OH)2,
crystals (Ca:P:: 1.3-2)
Magnesium, sodium, potassium, and carbonate ions are also
present among the bone salts
? Collagen :tensile strength;
? hydroxypatite : compressional strength
?Deposition and absorption of bone--remodeling of
bone
?Bone deposition and absorption are normally in
equilibrium.
?Continual physical stress stimulates osteoblastic
deposition and calcification of bone.
Bone Remodelling
Bone deposition & Bone resorption.
Requires 3 types of cells.
?Osteoblasts: secrete extracellular organic matrix
within which calcium phosphate crystal precipitate.
?Osteocyte: Retired osteoblast imprisoned within
bony wall around them.
?Osteoclasts: Resorb bone by secreting acids &
enzymes.They are cells of mononuclear phygocytic
system.
Mechanism of bone resorbtion
? Osteoclasts attaches to the part of bone
to be reabsorbed by integrins .
Forms "sealing zone"
? Proton pump(H+ dependent ATPases)migrate
From endosomes to the cell membrane.
Ph to 4 in this zone
Contd.
? The acidic pH dissolves hydroxypatite,
And proteases breakdown collagen.
Ca, P,and collagen breakdown products are
released into the interstitial fluid.
?Hydroxyproline is an index of bone resorbtion.
Factors controlling bone formationand
resorbtion
? GH, IGF, insulin, estrogen, testosterone, vit D ,
calcitonin, PDGF, Stimulates bone
formation.
? Cortisol inhibits bone formation.
? Parathormone, cortisol,thyroxine,PGs,IL-1&6,
TNF, Stimulates bone resorbtion.
?Despite supersaturation of calcium and phosphorus ions in
ECF hydroxypatite crystals fail to precipitate in other
tissues........... Why?
?Osteoid? Osteocytes?
?Mechanism of bone absorption by osteoclasts?
?The importance of exchangeble calcium ion in bone?
Physiological importance of continued deposition and
absorption of bone?
?Continual physical stress stimulates osteoblastic
deposition and calcification of bone....... How?
?Factors that control bone formation and resorption?
Applied physiology
? Osteoporosis : decrease in bone mass and
density.
? Involutional osteoporosis
?Postmenopausal osteoporosis
? Causes:Hyperparathyroidism,Hyperthyroidism,
Cushing's syndrome ,vit c ,alcoholism,etc.
? Treatment: Administeration of vit D and
calcium tablets.
Contd.
Osteopetrosis
? There is defective increase in bone formation.
? Rare & often severe disease.
? Osteoclasts are defective, unable to resorb
bone in usual fashion so osteoblasts operate
unopposed.
? Neurological and hematological abnormalities.
This post was last modified on 30 November 2021