U N I T IV                                     Textbook of Medical Physiology, 11th Edition                               ...
The Microcirculation        • Important in the transport of nutrients to          tissues.        • Site of waste product ...
Structure of Capillary Wall• Composed of unicellular layer of  endothelial cells surrounded by a  basement membrane.• Diam...
Solute and Fluid Exchange     Across Capillaries     • Most important means by      which substances are transferred      ...
Effect of Molecular Size on Passage    Through Capillary Pores   • The width of capillary     intercellular slit pores is ...
Relative Permeability of Muscle Capillary     Pores to Different-sized Molecules       Substance                     Molec...
Interstitium and Interstitial Fluid  • Space between cells is called   interstitium; fluid in this   space is called inter...
Determinants of Net Fluid     Movement across Capillaries (Starling     forces)                  Figure 16-5; Guyton and H...
Determinants of Net Fluid     Movement across Capillaries                   Figure 16-5; Guyton and Hall     • Plasma coll...
Starling Forces (Part I)     • Normal Capillary hydrostatic pressure is       approximately 17 mmHg.     • Interstitial fl...
Starling Forces (Part II)   • Presence of negative ions on proteins increases the colloid     osmotic effect of proteins–D...
Plasma Proteins and Colloid     Osmotic Pressure     • 75% of the total colloid osmotic pressure of       plasma results f...
Interstitial Colloid Osmotic     Pressure     • Interstitial protein conc. is approx. 3gm/dl     • The interstitial colloi...
Determinants of Net Fluid     Movement Across Capillaries                  Figure 16-5; Guyton and Hall       • Filtration...
Net Starting Forces in Capillaries                                                          mmHg          Mean forces tend...
Net Starting Forces in Capillaries                                             Figure opener;                             ...
Lymphatic System                                      • An accessory route by which                                     fl...
FUNCTIONS OF THE LYMPHATIC SYSTEM:1. It carries excess of interstitial fluid from interstitium into the blood. Rate of lym...
Determinants of Lymph Flow:                                     Figure 16-11; Guyton and Hall       • The degree of activi...
Determinants of Lymph Flow (cont..)                 Interstitial fluid hydrostatic pressure           Lymph Flow          ...
Determinants of Lymph Flow (cont..)        • Pressure on Lymphatics from outside:                 1. Skeletal Muscle Contr...
FACTORS CONTROLLING THEFORMATION OF TISSUE FLUID  1. Starlings Forces  2. Capillary permeability  3. Lymphatic obstruction...
Causes of Extracellular EdemaI. Increased capillary pressure      A. Excessive kidney retention of salt and water         ...
Causes of Extracellular Edema (cont..)II. Decreased plasma proteinsA. Loss of proteins in urine (nephrotic syndrome)B. Los...
Causes of Extracellular Edema (cont…) III. Increased capillary permeability         A. Immune reactions that cause release...
SAFETY FACTOR to prevent the developmentof edema        •      The development of edema is not an easy process. First the ...
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Interstitial fluid formation and edema by dr. mudassar ali roomi

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Interstitial fluid formation and edema by dr. mudassar ali roomi

  1. 1. U N I T IV Textbook of Medical Physiology, 11th Edition Chapter 16: The Microcirculation and Lymphatic System By Dr. Mudassar Ali Roomi (MBBS, M. Phil) GUYTON & HALLCopyright © 2006 by Elsevier, Inc.
  2. 2. The Microcirculation • Important in the transport of nutrients to tissues. • Site of waste product removal. • Over 10 billion capillaries with surface area of 500-700 square meters perform function of solute and fluid exchange. Figure 16-1; Guyton and HallCopyright © 2006 by Elsevier, Inc.
  3. 3. Structure of Capillary Wall• Composed of unicellular layer of endothelial cells surrounded by a basement membrane.• Diameter of capillaries is 4 to 9 microns (um). Figure 16-2; Guyton and Hall• Solute and water move across capillary wall via intercellular cleft (space between cells) or by plasmalemma vesicles.Copyright © 2006 by Elsevier, Inc.
  4. 4. Solute and Fluid Exchange Across Capillaries • Most important means by which substances are transferred between plasma and interstitial fluid is by diffusion. • Lipid soluble substances diffuse directly through cell membrane of capillaries (i.e. CO2, O2). • Lipid insoluble substances such as H2O, Na, Cl, glucose cross capillary walls via intercellular clefts. • Concentration differences across capillary enhances diffusion.Copyright © 2006 by Elsevier, Inc.
  5. 5. Effect of Molecular Size on Passage Through Capillary Pores • The width of capillary intercellular slit pores is 6 to 7 nanometers. • The permeability of the capillary pores for different substances varies according to their molecular diameters. • The capillaries in different tissues Figure 16-2; Guyton and Hall have extreme differences in their permeabilities. •Intestine, liver, kidney, choroid plexus have highly permeable capillaries. •Brain, lungs and skeletal muscles capillaries are less permeable.Copyright © 2006 by Elsevier, Inc.
  6. 6. Relative Permeability of Muscle Capillary Pores to Different-sized Molecules Substance Molecular Weight Permeability Water 18 1.00 NaCl 58.5 0.96 Urea 60 0.8 Glucose 180 0.6 Sucrose 342 0.4 Insulin 5000 0.2 Myoglobin 17,600 0.03 Hemoglobin 69,000 0.01 Albumin 69,000 .0001Copyright © 2006 by Elsevier, Inc.
  7. 7. Interstitium and Interstitial Fluid • Space between cells is called interstitium; fluid in this space is called interstitial fluid. • Two major types of solid structures in interstitium arecollagen fibers and proteoglycan filaments (coiledmolecules composed of hyaluronic acid). • Almost all fluid in interstitium is in form of gel (fluidproteoglycan mixtures); there is very little free fluidunder normal conditions. •Advantages of tissue gel are as follows: 1. It keep the cells in the tissues held apart so that spaces are Figure 16-4; Guyton and Hall available for the movement of fluid. 2. Tissue gel prevents the movement of fluid from the upper part of the body to lower part due to gravity. 3. It immobilizes the bacteria so prevents the spread of infectionCopyright © 2006 by Elsevier, Inc.
  8. 8. Determinants of Net Fluid Movement across Capillaries (Starling forces) Figure 16-5; Guyton and Hall • Capillary hydrostatic pressure (Pc)-tends to force fluid outward through the capillary membrane. • Interstitial fluid pressure (Pif)- opposes filtration when value is positive.Copyright © 2006 by Elsevier, Inc.
  9. 9. Determinants of Net Fluid Movement across Capillaries Figure 16-5; Guyton and Hall • Plasma colloid osmotic pressure (π c)- opposes filtration causing osmosis of water inward through the membrane • Interstitial fluid colloid pressure (π if) promotes filtration by causing osmosis of fluid outward through the membrane NP = (Pc – Pif)- (π p - π if)Copyright © 2006 by Elsevier, Inc.
  10. 10. Starling Forces (Part I) • Normal Capillary hydrostatic pressure is approximately 17 mmHg. • Interstitial fluid pressure in most tissues is negative 3. Encapsulated organs have positive interstitial pressures (+5 to +10 mmHg). • Negative interstitial fluid pressure is caused by pumping of lymphatic system. • Colloid osmotic pressure is caused by presence of large proteins.Copyright © 2006 by Elsevier, Inc.
  11. 11. Starling Forces (Part II) • Presence of negative ions on proteins increases the colloid osmotic effect of proteins–Donnan effect. • Plasma colloid osmotic = 28mmHg Plasma protein conc. = 7.3mg/dl • The reflection coefficient of capillaries quantitates the amount of protein that is reflected away from the capillary membrane. • Reflection coefficient of 1 means all proteins are reflected and none pass through pores, reflection coefficient of 0 means membrane is permeable to all proteins.Copyright © 2006 by Elsevier, Inc.
  12. 12. Plasma Proteins and Colloid Osmotic Pressure • 75% of the total colloid osmotic pressure of plasma results from the presence of albumin and 25% is due to globulins. gm/dl πp(mmHg) Albumin 4.5 21.8 Globulins 2.5 6.0 Fibrinogen 0.3 0.2 Total 7.3 28.0Copyright © 2006 by Elsevier, Inc.
  13. 13. Interstitial Colloid Osmotic Pressure • Interstitial protein conc. is approx. 3gm/dl • The interstitial colloid osmotic pressure is normally 8mmHgCopyright © 2006 by Elsevier, Inc.
  14. 14. Determinants of Net Fluid Movement Across Capillaries Figure 16-5; Guyton and Hall • Filtration rate = net filtration pressure (NFP) multiplied by the filtration coefficient • Filtration coefficient (Kf) is a product of surface area times the hydraulic conductivity of membraneCopyright © 2006 by Elsevier, Inc.
  15. 15. Net Starting Forces in Capillaries mmHg Mean forces tending to move fluid outward: Mean Capillary pressure 17.3 Negative interstitial free fluid pressure 3.0 Interstitial fluid colloid osmotic pressure 8.0 TOTAL OUTWARD FORCE 28.3 Mean force tending to move fluid inward: Plasma colloid osmotic pressure 28.0 TOTAL INWARD FORCE 28.0 Summation of mean forces: Outward 28.3 Inward 28.0 NET OUTWARD FORCE 0.3Copyright © 2006 by Elsevier, Inc.
  16. 16. Net Starting Forces in Capillaries Figure opener; Guyton and Hall • Net filtration pressure of .3 mmHg which causes a net filtration rate of 2ml/min for entire body.Copyright © 2006 by Elsevier, Inc.
  17. 17. Lymphatic System • An accessory route by which fluid and protein can flow from interstitial spaces to the blood • Important in preventing edema • Lymph is derived from interstitial fluid that flows into the lymphatics •Copyright © 2006 by Elsevier, Inc.
  18. 18. FUNCTIONS OF THE LYMPHATIC SYSTEM:1. It carries excess of interstitial fluid from interstitium into the blood. Rate of lymph flow is more than 3 liters/day. So this amount is drained by lym phatic system.2. It drains proteins and electrolytes from Interstitial space into lymphatic system. Lymphatic system drain 195 grams of blood proteins from interstitium back into the blood.3. It provides lymphocytes and antibodies into the circulation4. Removes bacteria and other microorganisims from the tissues.5. Lacteals are involved in the absorption and transport of lipids.6. Many large enzymes which are produced in the tissues get entry into the circulation through lymphatic system like histaminases and lipase.7. It maintains the negative interstitial fluid hydrostatic pressure.Copyright © 2006 by Elsevier, Inc.
  19. 19. Determinants of Lymph Flow: Figure 16-11; Guyton and Hall • The degree of activity of the lymphatic pump - smooth muscle filaments in lymph vessel cause them to contract - external compression also contributes to lymphatic pumpingCopyright © 2006 by Elsevier, Inc.
  20. 20. Determinants of Lymph Flow (cont..) Interstitial fluid hydrostatic pressure Lymph Flow Figure 16-9; Guyton and Hall Figure 16-10; Guyton and HallCopyright © 2006 by Elsevier, Inc.
  21. 21. Determinants of Lymph Flow (cont..) • Pressure on Lymphatics from outside: 1. Skeletal Muscle Contraction 2. Movements of different parts of body 3. Pressure by objects which come in contact on the outer surface of the body 4. Pulsations of nearby arteriesCopyright © 2006 by Elsevier, Inc.
  22. 22. FACTORS CONTROLLING THEFORMATION OF TISSUE FLUID 1. Starlings Forces 2. Capillary permeability 3. Lymphatic obstructionCopyright © 2006 by Elsevier, Inc.
  23. 23. Causes of Extracellular EdemaI. Increased capillary pressure A. Excessive kidney retention of salt and water 1. Acute or chronic kidney failure 2. Mineralocorticoid excess B. High venous pressure and venous constriction 1. Heart failure 2. Venous obstruction 3. Failure of venous pumps (a) Paralysis of muscles (b) Immobilization of parts of the body (c) Failure of venous valves C. Decreased arteriolar resistance 1. Excessive body heat 2. Insufficiency of sympathetic nervous system 3. Vasodilator drugs Copyright © 2006 by Elsevier, Inc.
  24. 24. Causes of Extracellular Edema (cont..)II. Decreased plasma proteinsA. Loss of proteins in urine (nephrotic syndrome)B. Loss of protein from denuded skin areas 1. Burns 2. WoundsC. Failure to produce proteins 1. Liver disease (e.g., cirrhosis) 2. Serious protein or caloric malnutrition Copyright © 2006 by Elsevier, Inc.
  25. 25. Causes of Extracellular Edema (cont…) III. Increased capillary permeability A. Immune reactions that cause release of histamine and other immune products B. Toxins C. Bacterial infections D. Vitamin deficiency, especially vitamin C E. Prolonged ischemia F. Burns IV. Blockage of lymph return A. Cancer B. Infections (e.g., filaria nematodes) C. Surgery D. Congenital absence or abnormality of lymphatic vesselsCopyright © 2006 by Elsevier, Inc.
  26. 26. SAFETY FACTOR to prevent the developmentof edema • The development of edema is not an easy process. First the safety factor has to be overcome to cause edema. • Safety factor is equal to 17 mm of Hg. • It has three components i.e. 1. Negative Interstitial Fluid Hydrostatic pressure: which contributes -3 mm of Hg. 2. Capacity of Lymphatic System: Increased amount of tissue fluid formed by 7 mm of Hg increase in Capillary pressure can be drained by lymphatic flow 3. Increased Washout of proteins from Interstitium: it contributes 7 mmHg. When there is increased formation of tissue fluid there is increased amount of fluid along with proteins that will enter the interstitium and then lymphatics for washing out. So the interstitial fluid colloid osmotic pressure can decrease from 8 mm of Hg upto 1mm of Hg before edema can start.Copyright © 2006 by Elsevier, Inc.

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