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The Microcirculation

The Microcirculation. Figure 16-1; Guyton and Hall. Structure of Capillary Wall. Figure 16-2; Guyton and Hall. Interstitium and Interstitial Fluid. Figure 16-4; Guyton and Hall. Determinants of Net Fluid Movement across Capillaries.

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The Microcirculation

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  1. The Microcirculation Figure 16-1; Guyton and Hall

  2. Structure of Capillary Wall Figure 16-2; Guyton and Hall

  3. Interstitium and Interstitial Fluid Figure 16-4; Guyton and Hall

  4. Determinants of Net FluidMovement across Capillaries • Capillary hydrostatic pressure (Pc)-tends to force fluid outward through the capillary membrane. • Interstitial fluid pressure (Pif)- opposes filtration when value is positive. Figure 16-5; Guyton and Hall

  5. Determinants of Net FluidMovement across Capillaries • Plasma colloid osmotic pressure ( c)- opposes filtration causing osmosis of water inward through the membrane • Interstitial fluid colloid pressure ( if) promotes filtration by causing osmosis of fluid outward through the membrane NP = Pc -  c - Pif +  if Figure 16-5; Guyton and Hall

  6. Plasma Proteins and ColloidOsmotic Pressure • 75% of the total colloid osmotic pressure of plasma results from the presence of albumin and 25% is due to globulins. gm/dl p(mmHg) Albumin 4.5 21.8 Globulins 2.5 6.0 Fibrinogen 0.30.2 Total 7.3 28.0

  7. Determinants of Net FluidMovement 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 membrane

  8. Forces Causing Filtration at theArteriole End of the Capillary mmHg Forces tending to move fluid outward: Capillary pressure 30 Negative interstitial free fluid pressure 3 Interstitial fluid colloid osmotic pressure 8 TOTAL OUTWARD FORCE 41 Forces tending to move fluid inward: Plasma colloid osmotic pressure 28 TOTAL INWARD FORCE 28 Summation of forces: Outward 41 Inward 28 NET OUTWARD FORCE 13

  9. Forces Causing Reabsorption at the Venous End of the Capillary mmHg Forces tending to move fluid inward: Plasma colloid osmotic pressure 28 TOTAL INWARD FORCE 28 Forces tending to move fluid outward: Capillary pressure 10 Negative interstitial free fluid pressure 3 Interstitial fluid colloid osmotic pressure 8 TOTAL OUTWARD FORCE 21 Summation of forces: Outward 21 Inward 28 NET INWARD FORCE 7

  10. Net Starling 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 0.3

  11. Net Starling Forces in Capillaries • Net filtration pressure of .3 mmHg which causes a net filtration rate of 2ml/min for entire body. Figure opener; Guyton and Hall

  12. Question Utilizing the data below, calculate the rate of net fluid movement across the capillary wall: Pressures (in mmHg) Plasma colloid osmotic = 20 Capillary hydrostatic = 20 Venous hydrostatic = 5 Arterial = 80 Interstitial hydrostatic = -5 Interstitial colloid osmotic = 5 Filtration coefficient = 10 ml/min/mmHg a. 0 ml/min d. 100 ml/min (Reabsorption) b. 10 ml/min (Filtration) e. 10 ml/min (Reabsorption) c. 100 ml/min (Filtration)

  13. Lymphatic System

  14. Determinants of Lymph Flow • The degree of activity of the lymphatic pump • smooth muscle filaments in lymph vessel cause them to contract • external compression also contributes to lymphatic pumping Figure 16-11; Guyton and Hall

  15. Determinants of Lymph Flow Interstitial fluid hydrostatic pressure Lymph Flow Figure 16-9; Guyton and Hall Figure 16-10; Guyton and Hall

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