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بسم الله الرحمن الرحيم

بسم الله الرحمن الرحيم. ﴿و ما أوتيتم من العلم إلا قليلا﴾. صدق الله العظيم الاسراء اية 58. Capillary Circulation. By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology. Interstitium and Interstitial Fluid. Interstitum.

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بسم الله الرحمن الرحيم

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  1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58 dr abdelaziz Hussein, Mansoura Faculty of Medicine

  2. Capillary Circulation By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology dr abdelaziz Hussein, Mansoura Faculty of Medicine

  3. Interstitium and Interstitial Fluid dr abdelaziz Hussein, Mansoura Faculty of Medicine

  4. Interstitum • 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

  5. Interstitum dr abdelaziz Hussein, Mansoura Faculty of Medicine

  6. Interstitial Fluid • 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

  7. Mechanisms of trans-capillary exchange of substances dr abdelaziz Hussein, Mansoura Faculty of Medicine

  8. Mechanisms of trans-capillary exchange of substances • Exchange of substances across the capillary wall occurs by; • Diffusion • Filtration • Osmosis • Vesicular transport • Diapedesis dr abdelaziz Hussein, Mansoura Faculty of Medicine

  9. I) Diffusion • ◊ 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

  10. I) Diffusion ◊ 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

  11. I) Diffusion 3. Capillary permeability: • a. Fat-soluble substancee.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. Waterpasses 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

  12. I) Diffusion 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

  13. I) Diffusion 3. Factors affecting Capillary permeability: dr abdelaziz Hussein, Mansoura Faculty of Medicine

  14. II) Filtration 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

  15. II) Filtration Hydrostatic Pressure Osmotic Pressure Water and dissolved molecules Water and dissolved molecules dr abdelaziz Hussein, Mansoura Faculty of Medicine

  16. II) Filtration • 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

  17. II) Filtration Capillary Osmotic Pressure Capillary Hydrostatic Pressure Interstitial Osmotic Pressure Interstitial Hydrostatic Pressure dr abdelaziz Hussein, Mansoura Faculty of Medicine

  18. 1. Capillary Hydrostatic Pressure (Cp) • 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

  19. 2) Plasma colloid osmotic pressure (Cπ) • 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

  20. 3) Interstitial fluid hydrostatic pressure (IFp) • 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 + 4 or 6 mmHg Interstitial Fluid Hydrostatic Pressure dr abdelaziz Hussein, Mansoura Faculty of Medicine

  21. 4) Interstitial fluid colloid osmotic pressure (Ifπ) • 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 Interstitial Fluid Hydrostatic Pressure dr abdelaziz Hussein, Mansoura Faculty of Medicine

  22. Formation and Drainage of the Interstitial Fluid dr abdelaziz Hussein, Mansoura Faculty of Medicine

  23. Formation and Drainage of Interstitial Fluid • 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

  24. Dynamics of Formation and Drainage of Interstitial Fluid a) At the arterial end of the capillary: Cη = 28 mmHg Cp = 30 mmHg IFp= -3 mmHg • So, the net outward force is13 mmHg at the arterial ends of the capillaries. Ifη= 8 mmHg dr abdelaziz Hussein, Mansoura Faculty of Medicine

  25. Dynamics of Formation and Drainage of Interstitial Fluid a) At the venous end of the capillary: Cη = 28 mmHg Cp = 10 mmHg IFp= -3 mmHg • So, the net inward force is 7 mmHg at the venous ends of the capillaries. Ifη= 8 mmHg dr abdelaziz Hussein, Mansoura Faculty of Medicine

  26. Dynamics of Formation and Drainage of Interstitial Fluid 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

  27. Starling's equilibrium for capillary exchange • 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

  28. THANKS dr abdelaziz Hussein, Mansoura Faculty of Medicine

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