baryar
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what happens when isotonic saline is injected intravenously.for an example consider the amount of isotonic saline injected intravenously to b one liter...............so what happens then?
obvioulsy at the time of infusion, it goes to extra-cellular compartment and remains there.
and about after 15-20 minutes?....................In this case here,NaCl can cross the cappilary membranes and bcaz of that 3/4 (about 750-775ml) of injected fluid will go into interstitial space (ISS) and about 225-250ml of this injected fluid will remain in vascular compartment.
question is that why would NaCl cross the capillary membranes when there is no difference in osmolarity?why not whole one liter of injected fluid remains in vascular compartment,
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| mildus
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if it is true, maybe it is because hydrostatic pressure would increase (because blood-interstitium exchange happens due to both osmotic and hydrostatic forces, contrary to interstitium-cell exchange which is only due to osmotic forces);
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| baryar
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ur answer is very much on the track,but to b xact,this exchange of fluid is due to the dilution of plasma proteins.
when u inject one liter of a fluid in vascular compartment,it obvioulsy is going to dilute plasma proteins.....thats the prime reason behind the fluid xchanges in this case.bcaz--->low concentration of plasma proteins---->more is the tendency of fluid to move out of capillaries.
if, instead of isotonic saline, u inject one liter of plasma in a patient,the entire (almost entire) of this one liter will remain in the vascular compartment bcaz in this case there will b no dilution of plasma proteins
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| mildus
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nice baryar
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| DrVirgo
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Baryar, great thinking question.
I understand your plasma infusion example.
I have a couple of points to ask:
-In case of isotonic fluid infusion, can we say that it is BOTH the increase in capillary hydrostatic pressure as well as the decrease in capillary oncotic pressure that causes the isotonic fluid to move from capillary (vascular space) to extravascular (ISF)?
-we know that isotonic fluid can move from vascular compartment to interstitial compartment, but what prevents it from entering the intracellular compartment?
-One more q with same concept:
What is the pathogenesis of Ascites in Cirrhosis? (Is it due to increased hydrostatic pressure in portal vein, or decreased oncotic pressure, or both?)
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| baryar
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i m not the authority,but i will try to xplain my concept of this topic
1= can we say that it is both the increase in hydrostatic pressure and decrease in capillary oncotic pressure that causes the fluid to move from capillary to interstiatial space?
no,it is not xactly the reason.this transfer is due to dilution of plasma membranes.hydrostatic pressure doesnt play a great role,
(let me xplain in detail as much as i got the concept from my first reading and use ur knowledge of transport across the membranes and forces governing it.)
u c that isotonic saline means that there is NaCl mixed in water.it means that osmolarity of the saline is equal to the body fluids.u know that in body fluids,osmolarity is contributed not only by sodium and chloride but there are some other substances also that contributes to the fluid osmolarity in body compartments.and in isotonic saline,only two particles (Na & Cl) contribute for aal the osmolarity and no other substance to contribute.
so we understand now that------------------>although isotonic saline=osmolarity of body fluids,yet its NaCl concentration (Na & Cl particles) are more as compared to their concentrations in body compartments.we know from our knowledge that NaCl can cross the capillar membranes.
since in this case the concentration gradient will push NaCl to go out of the capillaries into interstitial space,so NaCl will move out and along with it,it will take alot of water correspondingly.
had there been no dilution of plasma proteins,the normal concentration of plasma proteins would have restricted this movement of NaCl.
2= what prevents it from entering the intracellular compartment
firstly,NaCl doesnt cross cell membranes so cant enter intracellular.secondly,transport between ICF & ECf is bcaz of osmolarity differnces.NaCl that comes from capillary into ISS also brings alot of water with with so that osmolarity of no compartment is altered.aal compartments still have the same osmolarity.and when osmolarity is same ,there is no transport between ICF & ECF (ISS)
3=ascites in cirrhosis
this question i might b able to answer when i read medicine,or atleast read hepatic physiology or pathology.but so far as i know,ascites is of two types,
1) exudative (protein concentration less than 25g/l)or (serum-ascites albumin gradient above 1.5)
2)transudative (opposite of transudative)
so there must b some hell major role of proteins ofcourse.what i can recall is that transudative ascites is usually due to cirrhosis
keep smiling bcaz it never ends really
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| coolmavs
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mildus wrote:
if it is true, maybe it is because hydrostatic pressure would increase (because blood-interstitium exchange happens due to both osmotic and hydrostatic forces, contrary to interstitium-cell exchange which is only due to osmotic forces);
mildus, could you pls elaborate on what you have said in the brackets? I mean is this an assumptionor this is something that yo have read somewhere?
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| mildus
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Three compartments: intracellular (ICF), interstitium (ISF, intravascular (blood).
Fluid exchange between blood (capillaries) and interstitium is due to Starling's forces (oncotic and hydrostatic). And it's important to be noted that there is EQUILIBRIUM between blood and ISF.
Fluid exchange between interstitium and intracellular compartment is only due to osmotic (oncotic) forces. And, between ISF and ICF there is no equilibrium but GRADIENT.
There is a nice web site on this topic (Fluid Physiology) www.AnaesthesiaMCQ.com, here you can find many things.
Edited by mildus on 02/26/06 - 04:23 AM
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| baryar
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coolmavs,ur question has been satisfactarily answered by mildus.
i tried and i did xplain this aspect also in my post before ur post.mildus' post xplains it aal.and thing to remember is equilibrium and gradient factors.
keep smiling,bcaz it never ends really
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| coolmavs
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Had a query which I thinkis an extension of this, suppose we drink isotonic saline, then what will happen to our urine and what is ts mechanism?
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| mildus
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Well, blood volume is increased without changes of osmolarity; so there is increased blood pressure
in the kidney:
1. pressure-diuresis mechanism (increased diuresis due to increased pressure)
2. inhibition of ADH secretion (because hypovolemia or/and hyperosmolarity are stimuli for its secretion, and in this case osmolarity is normal and there is hypervolemia)
3. inhibition of RAAS (because the pressure is increased)
4. secretion of ANP due to activation of strech receptors in the heart --- increased diuresis and natriuresis
so, diuresis is increased (both sodium and water elimination)
this is my opinion, it doesn't necessarily mean it is true or complete
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| mildus
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In cirrhosis, ascites appears both due to decreased oncotic pressure (because cirrhotic liver doesn't produce enough albumins) and increased hydrostatic pressure (portal hypertension: the liver can't accept all the blood coming to it because it is cirrhotic, so blood stays more in portal vein)
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| baryar
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correction plz,for post #6 of this topic by me.it concerns the last part of the post regarding ascites discussion.
in my previous post(#6) it was like this -------------(i marked mistakes in blue and correction in bold italic black
this question i might b able to answer when i read medicine,or atleast read hepatic physiology or pathology.but so far as i know,ascites is of two types,
1) exudative(protein concentration less than 25g/l)or (serum-ascites albumin gradient above 1.5)
2)transudative (opposite of transudative)
so there must b some hell major role of proteins ofcourse.what i can recall is that transudative ascites is usually due to cirrhosis
now the correct xplaination is that,ascites is of two types,
1) transudative (protein concentration less than 25g/l)or (serum-ascites albumin gradient above 1.5)
2)exudative(opposite of transudative)
so there must b some hell major role of proteins ofcourse.what i can recall is that transudative ascites is usually due to cirrhosis
keep smiling bcaz it never ends really
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