ARTERIOLE 



EXCHANGE OF SUBSTANCES THROUGH CAPILLARY WALLS 



VENULE 



985 



30h 



TT pl 



PRESSURE 

 MM 20 



HG 



10 



(a) 



P, Capillary filtrate 



(b) 



Average 

 concentration 



(c) 



Highest 



concentration 



_"pl__ 



13 to 3.3 



(d) 



LYMPH 



Protein concentrations given in g /I00 ml fluid 



fig. 5.1. Schematic diagram of "an average limb capillary" to indicate approximate protein 

 concentrations in capillary nitrate, interstitial fluid, and lymph. 



table 5.1. Protein Concentrations in Extravascular 

 Fluids of the Limb 



fluid have to be inferred from studies on lymph. This 

 inference is valid after newly formed capillary filtrate 

 has washed out of the interstitial compartment the 

 fluid which was present before congestion and while 

 the interstitial fluid compartment is being constantly 

 irrigated by newly formed capillary filtrate with no 

 absorption possible. 



Hypoproteinemia in man, as mentioned above, 

 produces edema fluids with protein concentrations 

 ranging from 0.09 to 0.40 per cent. Weech et al. (374) 

 used chronic plasmapheresis to produce severe edema 

 of this type in dogs. Edema fluid contained between 

 0.04 and 0.4 g protein per 100 ml with all but a few 

 values below 0.25. Lymph protein in the same ani- 



mals ranged from 0.01 to 0.6, with almost all values 

 below 0.3. In some instances the protein content of 

 edema fluid was slightly higher than that of lymph 

 collected simultaneously, indicating again the possi- 

 bility of imperfect mixing of the interstitial fluid com- 

 partment and, consequently, some sequestration of 

 edema fluid. Capillary filtrate, however, has not 

 been studied and so its protein content can only be 

 inferred. Lessened permeability to protein has been 

 suggested (374) but not proved so far. Sieving of 

 protein molecules may be involved (see section 10). 



Massive injury in burns, produced by immersing 

 the extremities of anesthetized dogs in hot water 

 (48, 99, 100, 119, 120) increases lymph flow con- 

 spicuously and increases the protein in lymph to 

 between 3.5 and 5 g per 100 ml. In view of the known 

 effects of injury on capillary permeability to protein 

 (200) it is safe to infer that protein concentrations in 

 capillary filtrate and interstitial fluid are equally 

 high; particularly because lymph flow is rapid and 

 the interstitial compartment is well irrigated by 

 capillary filtrate. 



For contracting muscle, information is still meager. 

 White et al. (379) found in dogs that while the flow of 

 lymph was much increased by exercise, its protein 

 content declined to between 0.5 and 1.5 per cent, 

 average 1 .0, and then remained constant as long as 

 exercise continued. The elevations of capillary blood 

 pressure and of interstitial fluid pressure during exer- 

 cise have already been described in sections 2D and 4. 

 Inferences concerning capillary filtrate and inter- 

 stitial fluid are unjustified because the lymph col- 



