1. Unit Four: The Circulation
Chapter 16: The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow
Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Structure of the Microcirculation/Capillary Systems
Microcirculation- transport of nutrients to the tissues
and the removal of cell wastes
The microcirculation of each organ is
organized specifically to meet that organ’s needs.
Fig. 16.1

3. Structure of the Microcirculation/Capillary Systems
Fig Structure of the capillary wall

4. Structure of the Microcirculation/Capillary Systems
Special Types of Pores in Capillaries
Brain-tight junctions between the capillary endothelial
cells so only small molecules pass in and out
Liver-clefts are wide open so that almost all
dissolved substances can pass
GI tract-midway between those of the muscle and liver
Kidney-fenestrated; small openings to increase
filtration through the glomerulus

5. Flow of Blood in the Capillaries
Regulation of Vasomotion
Average Function of the Capillary System

6. Diffusion Through the Capillary Membrane
Exchange of Water, Nutrients, etc. Between the Blood and Interstitial Fluid
Diffusion Through the Capillary Membrane
Fig. 16.3

7. Exchange (cont)
Lipid soluble substances diffuse directly through
the cell membranes of the capillary endothelium
Water soluble, non-lipid soluble, substances
diffuse through intercellular “pores” in the
membrane
Effect of molecular size on passage through the
pores

8. Exchange (cont) Substance Molecular Weight Permeability Water 18 1.00
Table Relative permeability of skeletal muscle capillary pores to different size molecules
Substance
Molecular Weight
Permeability
Water 18
1.00
NaCl
58.5
0.96
Urea 60
0.80
Glucose
180
0.60
Sucrose
342
0.40
Inulin
5000
0.20
Myoglobin
17600
0.03
Hemoglobin
68000
0.01
Albumin
69000
0.001

9. Exchange (cont)
Effect of concentration difference on net rate of
diffusion through the capillary membrane
Net rate is proportional to the concentration
difference between the two sides of the
membrane

10. Interstitium and Interstitial Fluid
Fig Structure of the interstitium; containing collagen
bundle fibers and proteoglycan filaments

11. Interstitium (cont.)
“Gel” in the Interstitium - because of the
proteoglycan filaments and the fluids
entrapped within them, the consistency
is that of a “gel.” The fluid diffuses but
not flow.
Free Fluid in the Interstitium – usually <1%
unless there is edema and then it expands
rapidly

12. Filtration Across Capillaries: Determined by Hydrostatic and Colloid Osmotic Pressures, as well as the Capillary Filtration Coefficient
Hydrostatic pressure in the capillaries tends to force
fluid and its dissolved substances through the pores
into the interstitial spaces.
Colloid osmotic pressure caused by the plasma
proteins tends to cause fluid to move into the blood.

13. Fluid Filtration (cont.)
Hydrostatic and Colloid Osmotic Forces Determine
Fluid Movement Through the Capillary Membrane
Fig Fluid pressure and colloid osmotic pressure forces operate at
the capillary membrane, moving fluid either outward or inward.

14. Fluid Filtration (cont.)
Capillary pressure tends to force fluid outward
Interstitial fluid pressure tends to force fluid inward
Capillary plasma colloid osmotic pressure tends to
cause osmosis of fluid inward
d. Interstitial fluid colloid osmotic pressure tends to cause
osmosis of fluid outward
The sum of these forces—the net filtration pressure
+ net fluid filtration
- fluid absorption

15. Fluid Filtration (cont.)
Interstitial Fluid Hydrostatic Pressure- pumping by
the lymphatic system is the basic cause of negative
interstitial fluid pressure
Plasma Colloid Osmotic Pressure - caused by plasma
proteins

16. Fluid Filtration (cont.)
Effect of different plasma proteins on colloid osmotic pressure
Proteins
g/dl
Plasma colloid
Osmotic pressur
Albumin
4.5
21.8 mm Hg
Globulins
2.5
6.0 mm Hg
Fibrinogen
0.3
0.2 mm Hg
Total
7.3
28.0 mm Hg

17. Lymphatic System
Fig Lymphatic System

18. Lymphatic System (cont.)
Lymph channels of the body
Terminal lymphatic capillaries and their permeability
Formation of lymph

19. Fig. 16.8 Special structure of the lymphatic capillaries that permits passage of
substances of high molecular weight into the lymph.

20. Lymphatic System (cont.)
Rate of Lymph Flow- effect of interstitial fluid pressure on lymph flow
Fig. 16.9

21. Lymphatic System (cont.)
Factors That Increase Interstitial Fluid Flow
Elevated capillary hydrostatic pressure
Decreased plasma colloid osmotic pressure
Increased interstitial fluid colloid osmotic
pressure
d. Increased permeability of the capillaries

22. Lymphatic System (cont.)
Lymphatic Pump Increases Lymph Flow
Fig Structure of lymphatic capillaries and a collecting lymphatic,
showing also the lymphatic valves.