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بسم هللا الرحمن الرحيم ﴿و ما أوتيتم من العلم إال قليال﴾ صدق هللا العظيم 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