صدق الله العظيم الاسراء اية 58 dr abdelaziz hussein, mansoura faculty of...

صدق الله العظيم 58االسراء اية

dr abdelaziz Hussein, Mansoura Faculty of Medicine

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Dr. Abdel Aziz M. HusseinDr. Abdel Aziz M. HusseinLecturer of Medical PhysiologyLecturer of Medical Physiology

Member of American Society of PhysiologyMember of American Society of Physiology


• Is the space ( ) the cells, it constitutes approximately 1/6 of the body tissues.

• It is composed of 2 types of solid structures:

• a. Collagen fiber bundles → are long and very strong and therefore provide most of the tensional strength of the tissues.

• b. Proteoglycan filaments → are extremely thin, colloid molecules.

• They form a sponge of very fine reticular filaments that fill all the spaces ( ) the collagen fibers, the cells.


• It is mainly entrapped in the minute spaces among the

proteoglycan filaments.

• The combination of the proteoglycan filaments and the

fluid entrapped within them has the characteristics of a gel

→ called the tissue gel.


• Exchange of substances across the capillary wall

occurs by;

1. Diffusion

2. Filtration

3. Osmosis

4. Vesicular transport

5. Diapedesis


◊ ◊ Def,Def,•It is a passive process by which water and dissolved

substances are transferred ( ) the plasma and interstitial fluid.


◊ ◊ Factors affecting it:Factors affecting it:

•1. Concentration gradient:1. Concentration gradient:

•Diffusion occurs from higher to a lower concentration.

•2. Surfaces Area:2. Surfaces Area:

•The greater the surface area available for diffusion, the

more will be the diffusion.

•3. Capillary permeability:3. Capillary permeability:

•The capillary wall acts as a semipermeable membrane :


3. Capillary permeability:3. Capillary permeability:

•a. Fat-soluble substancea. Fat-soluble substance e.g. CO2, O2 and alcohol → diffuse

directly through the capillary wall (no need for pores)

•b. Water soluble substancesb. Water soluble substances (crystalloids), e.g. Na, K,

glucose and amino acids → diffuse only through the capillary

pores.

•c. Waterc. Water passes through both ways (i.e. directly and through the

pores) and in both directions→ because of its small MW and high

kinetic energy of the molecule.


3. Capillary permeability:3. Capillary permeability:

•d. Substances with high M.W. d. Substances with high M.W. (colloids) as proteins, are either

retained in the blood or are allowed to pass with difficulty

• The capillaries of the glomeruli of the kidney is the least permeable to protein so the normal urine is free from proteins

• Capillaries with high permeability e.g. liver sinusoids, allow more proteins to pass into the interstitial fluid.

• Capillary permeability to protein is not identical in the different parts of the body


3. Factors affecting Capillary permeability:3. Factors affecting Capillary permeability:

Capillary Permeability↑ ↓ Capillary permeability

Hypocalcaemia Hypercalcaemia

Acidosis Alkalosis

Vitamin C and P deficiency Large doses of Vitamin C

Hypoproteinemia Hyperproteinemia

Inflammation , allergic

reaction , extreme cold (5°C)

or extreme hot (45°) and

Oxygen lack

Glucocorticoid hormone


Def. Def. •It is the passage of a bulk flow of fluid across the capillary

membrane under the control of hydrostatic or osmotic pressure difference.


Water and dissolved molecules

Water and dissolved molecules

Hydrostatic Pressure

Osmotic Pressure


• 4 forces (called Starling Forces) (called Starling Forces)

1) Capillary hydrostatic pressure (Cp)

2) Plasma colloid osmotic pressure (Cπ)

3) Interstitial fluid hydrostatic pressure (Ifp)

4) Interstitial fluid colloid osmotic pressure(IFπ)


Capillary Hydrostatic Pressure

Capillary Osmotic Pressure

Interstitial Hydrostatic Pressure

Interstitial Osmotic Pressure dr abdelaziz Hussein, Mansoura

Faculty of Medicine

Capillary Hydrostatic Pressure

30 mmHg 17.3 mmHg 10 mmHg

• This force tends to move fluid outward through the capillary membrane→ main filtering force.


Plasma Colloid Osmotic Pressure

28 mmHg

• This force tends to cause osmosis of fluid inward through the capillary membrane → is the main absorbing force• It is about 28 mmHg, 19 mmHg by protein and 9 mmHg by the positively charged ions (cations) mainly Na that are held

in the plasma by the Donnan equilibrium effect → ↑ the colloidal osmotic pressure of the plasma by 50%.

• About 80% of the colloid osmotic pressure of the plasma results from the albumin, 20% from globulins, and almost none from the fibrinogen


Interstitial Fluid Hydrostatic Pressure

- 3 mmHg

• This force tends to move fluid inward through the capillary membrane when it is +ve, but outward when it is -ve.

• It is about -3 mmHg and is called -ve interstitial fluid pressure• However, in all tissues with tight fibrous coverings that hold the

tissues tightly together, such as the kidneys and the brain, the pressure is usually more +ve (i.e. about +6 mmHg in the kidney and +4 mmHg in the brain).

+ 4 or 6 mmHgdr abdelaziz Hussein, Mansoura Faculty of Medicine

Interstitial Fluid Hydrostatic Pressure 8 mmHg

• It is the force which tends to cause osmosis of fluid outward through the capillary membrane.

• It is about 8 mmHg → as average protein concentration of the interstitial fluid is about 3 gm/100 ml.

•The total quantity of protein in the entire interstitial fluid of the body is actually greater than that in the plasma itself because the

volume of the interstitial fluid (12 liters) is 4 times the volume of the plasma (3 liters).

•The average protein concentration of the interstitial fluid is usually 40% of that in the plasma.


• About 20 liters of fluid are filtered every day at the arterial ends of capillaries, 18 liters of them are reabsorbed back at the venous

ends, and the remaining 2 liters are drained by the lymphatic system.


Cp = 30 mmHg

Cη = 28 mmHg

Ifη= 8 mmHg

IFp= -3 mmHg

a) At the arterial end of the capillary:a) At the arterial end of the capillary:

• So, the net outward force is13 mmHg at the arterial ends of the capillaries.dr abdelaziz Hussein, Mansoura

Faculty of Medicine

Cp = 10 mmHg

Cη = 28 mmHg

Ifη= 8 mmHg

IFp= -3 mmHg

a) At the venous end of the capillary:a) At the venous end of the capillary:

• So, the net inward force is 7 mmHg at the venous ends of the capillaries.dr abdelaziz Hussein, Mansoura

Faculty of Medicine

a) At the venous end of the capillary:a) At the venous end of the capillary:

• The venous capillaries are more numerous and more permeable than the arterial capillaries, so that less pressure is required to cause inward movement of fluid

• The reabsorbing pressure at the venous ends is less than the filtration pressure.


• Starling states that under normal conditions, a state of near equilibrium exists at the capillary membrane→ so the amount of

fluid filtering outward from some capillaries equals almost exactly the quantity of fluid that is returned to the circulation by absorption

through other capillaries.


THANKS


صدق الله العظيم الاسراء اية 58 dr abdelaziz hussein, mansoura faculty of...

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