Interstitial Fluid - Copy

8/2/2019 Interstitial Fluid - Copy

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The

Interstitial fluid


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Tissue cell

=12 L


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Exchange of nutrients and

substances through thecapillary wall

Bulk flowDiffusion


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The kinetic movement of molecules from an area

of high concentration to an area of lowconcentration.

Diffusion

The main mechainism


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Rate of

diffusion

Molecular size

Solubility

Temperature

Surface area


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Pathways of diffusion

Water&

watersoluble

proteins lipid

Soluble,O2,CO2

Slit poresFenestae

Pinocytosis

(Vesicular

Transcellular

transport


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Slit pores

fenestrae

Transcellulartransport


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Bulk flow

= increased diffusion

It is the process by which substances areforced through a membrane because ofdifference in pressure on both sides of themembrane


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Bulk flow=increased diffusion

FILTRATION REABSORPTION


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Filtration

It is an increased diffusionof water and solutesthrough a membrane

towards the opposite side ofhigh hydrostatic pressure.

It is bulk flow of water and

solutes from the plasmainto the interstitial fluidthrough the capillary wall.


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Reabsorption

It is an increased diffusionof water and solutesthrough a membranetowards the same side of

high osmotic pressure.

It is bulk flow of water and

solutes from theinterstitial fluid into theplasma through thecapillary wall


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Fluid Movement depends on

Starling Factors:

1-capillary Pressure

2-Interstitial Fluid Pressure3-Plasma Colloid Osmotic Pressure4-Interstitial Fluid Colloid Osmotic

Pressure


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At the arterialend.

At thesummit(loop)

At the venous

1-Capillary pressure


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Factors affecting the capillary pressure

1)Capillary

level:Below the heartor

Above the heart


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2)Venouspressure:


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2)Venous

pressure:Venous obstruction by a tumor outside or athrombus inside.increased venous pressure by right heart

failure

the enlarged uterus in the last three monthsof pregnancy.Nephrosis.



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3) Condition of arterioles:

1- Dilation

2-Constriction



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4)Arterial blood pressure: Arterial blood pressure tends to Thecapillary pressure

However, acute control of local blood flow bringscapillary pressure back to normal.


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Increased arterialpressure

Increased capillarypressure


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5) Visceral characteristics:

In the viscera, the capillary pressure differs

according to the nature of the local mechanism.For example,

The renal glomeruli :60 mmHg.



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The intestinal capillaries:10-20 mmHg



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The liver : 6 mmHg



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The lungs : 8-10 mmHg.



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Either slightly positive (+1 or

+2 mmHg) i.e. moves thefluid inwardor

slightly negative (-6 or -8mmHg)i.e. moves the fluid outward.

2-Interstitial fluid

pressure


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Normal value:28 mmHg

Causes of plasmaosmotic pressure

a-75% from the albumin

b-25% from the globulinsc-very small percentagefrom the fibrinogen

3-Plasma colloid

osmotic pressure


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Why the concentration ofproteins in the plasma averages

over three times as much asthat in the interstitial fluid?

(7.5 g/ 100 ml the plasma versus

2 g/ 100 ml in the interstitialfluid).


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4-Interstitial fluid

colloid osmoticpressure

Average is 5 mmHgDepends on interstitialprotein concentration

which varies in differentorgans

6gm/100ml

1.4gm/dl

4gm/100ml


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Dynamics of fluid exchange(tissue fluid formation)

Total inward

force=28+1=29

Total outward force=30+5=40

Net outward force=40-29=11

Total inwardforce=28+1=29

Total outwardforce=15+5=20

Net inward force=29-20=9


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At the arterial end

1. Filtration of fluidthrough capillarypores .

2. It causes 24L ofplasma fluid to befiltered/day out ofcapillary tointerstitial spaces.

1. About 90% of filteredfluid at arterial end arereabsorbed at venousend.

At the venous end

10%


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However, in some capillaries this balance

is different

Filtration Reabso


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Distribution of fluid between plasmaand interstitial fluid

1.The inward and outward forces are nearly equal.

2. The rate of net movement across the capillarymembrane is normally very low.

3. Volumes of both blood and interstitial fluidnormally changes very little from hour to hour.

Under normal

conditions


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Decreased blood volume (hypotension) or edema

If filtration >reabsorption


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Increased blood volume and tissue dehydration

If reabsorption>filtration


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Differences betweenfiltration

anddiffusion


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Lymphatic

CirculationFunctions:

1- The lymphatic systemremoves from the interstitium

albumin and othermacromolecules which haveescaped from themicrocirculation.

2- Lymphatics drain fluid fromthe interstitium to maintain itsnormal structure.


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Lymphatic

CirculationLymphatic flow rate:

2 L/day for the entire body, containing 200g ofproteins. most lymph comes from the liver and GIT

Mechanism of flow:

Lymph is mobilized by the contraction of largelymphatics and skeletal muscles. The lymphatics havean extensive system of one-way valves to maintain the

flow of lymph to the heart.


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Lymphatic

CirculationImportanceThe lymphatic system represents the only mechanismof returning interstitial proteins to the circulatorysystem.


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/ /

Hr&c.o.pS.V HR C.O.P

70 ml 70 b\m 5 l\m Non

atheletes

During rest

120 ml 45-55 b\m 5 l\m atheletes

120 ml 180 b\m 22-25 l\m Non-atheletes Duringexercise

200 ml 180 b\m 35-36 l\m atheletes

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Interstitial Fluid - Copy