صدق الله العظيم الاسراء 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

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

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

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: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 : dr abdelaziz Hussein, Mansoura Faculty of Medicine

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. dr abdelaziz Hussein, Mansoura Faculty of Medicine

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 dr abdelaziz Hussein, Mansoura Faculty of Medicine

3. Factors affecting Capillary permeability:3. Factors affecting Capillary permeability: ↓ Capillary permeability Capillary Permeability↑ HypercalcaemiaHypocalcaemia AlkalosisAcidosis Large doses of Vitamin CVitamin C and P deficiency HyperproteinemiaHypoproteinemia Glucocorticoid hormoneInflammation, allergic reaction, extreme cold (5°C) or extreme hot (45°) and Oxygen lack dr abdelaziz Hussein, Mansoura Faculty of Medicine

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

Water and dissolved molecules Hydrostatic Pressure Osmotic Pressure dr abdelaziz Hussein, Mansoura Faculty of Medicine

(called Starling Forces)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 Hydrostatic Pressure Capillary Osmotic Pressure Interstitial Hydrostatic Pressure Interstitial Osmotic Pressure dr abdelaziz Hussein, Mansoura Faculty of Medicine

Capillary Hydrostatic Pressure 30 mmHg17.3 mmHg10 mmHg This force tends to move fluid outward through the capillary membrane→ main filtering force. dr abdelaziz Hussein, Mansoura Faculty of Medicine

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 dr abdelaziz Hussein, Mansoura Faculty of Medicine

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 mmHg dr 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. 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

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. 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