Download capillary circulation II

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‫االسراء اية ‪58‬‬
‫‪dr abdelaziz Hussein, Mansoura Faculty‬‬
‫‪of Medicine‬‬
By
Dr. Abdel Aziz M. Hussein
Lecturer of Medical Physiology
Member of American Society of Physiology
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 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.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 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.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• Exchange of substances across the capillary wall
occurs by;
1. Diffusion
2. Filtration
3. Osmosis
4. Vesicular transport
5. Diapedesis
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
◊ Def,
•It is a passive process by which water and dissolved
substances are transferred ( ) the plasma and interstitial
fluid.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
◊ Factors affecting it:
• 1. Concentration gradient:
• Diffusion occurs from higher to a lower concentration.
• 2. Surfaces Area:
• The greater the surface area available for diffusion, the
more will be the diffusion.
• 3. Capillary permeability:
• The capillary wall acts as a semipermeable membrane :
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
3. Capillary permeability:
• a. Fat-soluble substance e.g. CO2, O2 and alcohol → diffuse
directly through the capillary wall (no need for pores)
• b. Water soluble substances (crystalloids), e.g. Na, K,
glucose and amino acids → diffuse only through the capillary
pores.
• c. 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.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
3. Capillary permeability:
• d. Substances with high M.W. (colloids) as proteins, are either
retained in the blood or are allowed to pass with difficulty
• Capillary permeability to protein is not identical in the different
parts of the body
• 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.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
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
Glucocorticoid hormone
reaction , extreme cold (5°C)
or extreme hot (45°) and
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
Oxygen lack
Def.
• It is the passage of a bulk flow of fluid across the capillary
membrane under the control of hydrostatic or osmotic pressure
difference.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
Hydrostatic
Pressure
Osmotic
Pressure
Water and
dissolved
molecules
Water and
dissolved
molecules
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 4 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)
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
Capillary Capillary
Hydrostatic Osmotic
Pressure Pressure
Interstitial
Osmotic
Pressure
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
Interstitial
Hydrostatic
Pressure
• This force tends to move fluid outward through the
capillary membrane→ main filtering force.
Capillary Hydrostatic Pressure
30 mmHg
17.3 mmHg 10 mmHg
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 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
Plasma Colloid Osmotic Pressure
28 mmHg
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 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).
- 3 mmHg
dr abdelaziz Hussein, Mansoura Faculty
Interstitial Fluid Hydrostatic
Pressure
of Medicine
+ 4 or 6 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.
8 mmHg
dr abdelaziz Hussein,
Mansoura
Faculty
Interstitial
Fluid
Hydrostatic
Pressure
of Medicine
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 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.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
a) At the arterial end of the capillary:
Cp = 30
mmHg
Cη = 28
mmHg
IFp= -3 mmHg
• So, the net outward force is13 mmHg at the
dr abdelaziz Hussein, Mansoura Faculty
arterial ends of the capillaries.
of Medicine
Ifη= 8 mmHg
a) At the venous end of the capillary:
Cp = 10
mmHg
Cη = 28
mmHg
IFp= -3 mmHg
• So, the net inward force is 7 mmHg at the
dr abdelaziz Hussein, Mansoura Faculty
venous ends of the capillaries.
of Medicine
Ifη= 8 mmHg
a) At the venous end of the capillary:
• The reabsorbing pressure at the venous ends is less than the
filtration pressure.
• 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
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
• 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.
dr abdelaziz Hussein, Mansoura Faculty
of Medicine
THANKS
dr abdelaziz Hussein, Mansoura Faculty
of Medicine