The Microcirculation
Figure 16-1;
Guyton and Hall
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Structure of Capillary Wall
Figure 16-2; Guyton and Hall
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Interstitium and Interstitial Fluid
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Figure 16-4; Guyton and Hall
Determinants of Net Fluid
Movement across Capillaries
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.
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Determinants of Net Fluid
Movement across Capillaries
Figure 16-5; Guyton and Hall
• 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
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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.
Albumin
Globulins
Fibrinogen
Total
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gm/dl
4.5
2.5
0.3
7.3
p(mmHg)
21.8
6.0
0.2
28.0
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 membrane
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Forces Causing Filtration at the
Arteriole End of the Capillary
mmHg
Forces tending to move fluid outward:
Capillary pressure
Negative interstitial free fluid pressure
Interstitial fluid colloid osmotic pressure
TOTAL OUTWARD FORCE
30
3
8
41
Forces tending to move fluid inward:
Plasma colloid osmotic pressure
TOTAL INWARD FORCE
28
28
Summation of forces:
Outward
Inward
NET OUTWARD FORCE
41
28
13
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Forces Causing Reabsorption at
the Venous End of the Capillary
mmHg
Forces tending to move fluid inward:
Plasma colloid osmotic pressure
TOTAL INWARD FORCE
Forces tending to move fluid outward:
Capillary pressure
Negative interstitial free fluid pressure
Interstitial fluid colloid osmotic pressure
TOTAL OUTWARD FORCE
Summation of forces:
Outward
Inward
NET INWARD FORCE
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28
28
10
3
8
21
21
28
7
Net Starling Forces in Capillaries
Mean forces tending to move fluid outward:
Mean Capillary pressure
Negative interstitial free fluid pressure
Interstitial fluid colloid osmotic pressure
TOTAL OUTWARD FORCE
mmHg
17.3
3.0
8.0
28.3
Mean force tending to move fluid inward:
Plasma colloid osmotic pressure
TOTAL INWARD FORCE
28.0
28.0
Summation of mean forces:
Outward
Inward
NET OUTWARD FORCE
28.3
28.0
0.3
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Net Starling 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.
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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)
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Lymphatic System
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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
pumping
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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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