slides - bone physio

DAILY TURNOVER RATE RATES FOR CALCIUM IN ADULT
nIntake-------------------------------1000mg
nIntestinal absorption-----------------350mg
nSecretion in GI juices----------------250mg
nNet absorption over secretion-------100mg
nLoss in feces-------------------------900mg
nExcretion in urine--------------------100mg


n90% of calcium in the GMF is reabsorbed in proximal tubules, loops of Henle and early distal tubules
n10% is reabsorbed in the late distal tubules and early collecting ducts – selective

INTESTINAL AND URINARY EXCRETION OF PHOSPHATE
nAlmost all dietary phosphate is absorbed into the blood from the gut
nPhosphate is renal threshold substance
nKidneys regulate ECF conc. of phosphate by altering rate of phosphate excretion in accordance with plasma concentration

cholecalciferol(vit. D3)
liver
25-hydroxycholecalceferol
kidney parathyroid
activation
hormone
1,25-dihydroxycholecalciferol
intestinal epithelium
Calcium calcium alkaline
Binding stimulated phosphate
Protein ATPase

intestinal absorption of calcium
plasma calcium ion concentration
inhibitory

VITAMIN D AND ITS ROLE IN CALCIUM AND PHOSPHATE ABSORPTION
nPotent effect on increasing calcium absorption from the intestine
nImportant effect on bone deposition and reabsorption
nInactive substance thus will have to be activated

VITAMIN D AND ITS ROLE IN CALCIUM AND PHOSPHATE ABSORPTION
INTESTINE ;
ABSORPTION
BONE ;
CALCIUM
ABSORPTION
DEPOSITION

CALCIUM IN THE PLASMA AND INTERSTITIAL FLUID

nConcentration is about 2.4 mmol/liter
n3 forms
1. 40% combined with plasma protein
2. 10% diffusable but combine with other
substances in plasma and interstitial fluid
3. 50% diffusable and ionized
nIonized calcium is important in its effects in the
1. heart
2. nervous system
3. bone formation

NON-BONE PHYSIOLOGICAL EFFECTS OF ALTERED CALCIUM AND PHOSPHATE CONCENTRATION IN THE BODY FLUIDS

nChange in phosphate level - no significant immediate effects on the body
nSlight elevation or decrease of calcium ion concentration can cause extreme physiological effects
tetany from hypocalcemia
nNervous system becomes
Increase in neuronal membrane permeability to sodium ions
nEasy initiation of action potential
nTetanic muscle contraction
nSeizzures
nCarpopedal spasm
nBelow normal value of 9.6 to 6mg/dl

hypercalcemia
nNervous system becomes
nReflex activities are sluggish
nDecrease QT interval of the heart
nConstipation
nLack of appetite
nEffects appear when level is 12mg/dl


BONE AND ITS RELATIONS TO EXTRACELLULAR CALCIUM AND PHOSPHATE
nBone is
- 30% matrix
- 70% calcium salt
nOrganic matrix
- 90-95% collagen fibers
- 5-10%ground substance

BONE SALTS
nCrystalline salts deposited in the organic matrix of bone are principally composed of calcium and phosphate known as hydroxyappatite
nBone stregnth depends on
collagen fibers-tensile strength
calcium phospate- compresional strength

PRECIPITATION AND ABSORPTION OF CALCIUM AND PHOSPHATE IN BONE
nInhibitors are present in all tissues of the body to prevent precipitation
- pyrophosphate
nHydroxyapatite crystals fail to precipitate in normal tissues except in bone

MECHANISM OF BONE CALCIFICATION
nOsteoblasts secrete
collagen monomers
ground substance(mainly proteoglycans)
nPolymerization of collagen monomers to collagen fibers – resulting to formation of
osteoid
nEntrapped osteoblasts become
osteocytes

nFew days after osteoid is formed calcium precipitates on the surface of the collagen fibers
nFinal product of precipitation is hydroxyappatite
nSome remains as amorphous form of salts
nDeposition of calcium maybe due to neutralization of the inhibitor pyrophosphate

PRECIPITATION OF CALCIUM IN NONOSEOUS TISSUES UNDER ABNORMAL CONDITIONS
nArteriosclerosis
nMakes arteries bone-like tubes
nMay deposit also in degenerating tissues and blood clots
nDisappearance of inhibitor in the tissues

EXCHANGEABLE CALCIUM
RAPID BUFFERING MECHANISM - balance or equillibrium of bone calcium and ECF calcium

REMODELING OF BONE
nOsteoblasts – deposition of bone
nOsteoclasts - absorption of bone
– large phagocytic multinucleated cells
nMechanism of absorption
- send out villus like projections
- secretions from villi
1. proteolytic enzymes to dissolve matrix
2. acids like lactic and citric acids to cause solution of bone salt


VALUE OF CONTINUAL REMODELING OF BONE
n1. bone adjusts its strength in proportion to the degree of bone stress
n2. Shape of bone can be rearranged for proper support of mechanical forces by deposition and absorption of bone in accordance with stress patterns
n3. New organic matrix is needed as the old matrix degenerates


CONTROL OF THE RATE OF BONE DEPOSITION BY BONE STRESS
ndeposition of bone at points of
compressional stress -piezoelectric effect
nCompression of bone causes a negative electrical potential in compressed areas and positive potential elswhere
nOsteoblastic activity is noted in negative end of the current and usual osteoclastic activity elswhere

REPAIR OF FRACTURE
nFracture activates all osteoblast involved in the the break
nIncrease in new osteoblasts from osteoprogenitor cells
nCallus formation – bulge of osteoblastic tissue
nBlood alkaline phosphate is used as indicator of bone deposition