1042 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. I. A: Ratio of lymph volume flow 

 (ml/min) after the start of the infusion to 

 the preinfusion (control) lymph volume flow 

 plotted against the time after the beginning 

 of the infusion. The 250-ml infusions lasted 

 approximately 8 min, the 500-ml infusions 

 lasted 15 min, the 1000-ml infusions lasted 

 30 min, and the 2000-ml infusions lasted 

 approximately 1 hour. Average control 

 lymph flow for these experiments is 0.5 ml/min. 

 B: Ratio of albumin flow (ml/min) after the 

 start of the infusion to the preinfusion (con- 

 trol) lymph albumin flow plotted against 

 time after the beginning of the same experi- 

 ments as in A. Numerals to the right of the 

 infusion volumes are the numbers of experi- 

 ments which were averaged in each group. 

 Average control albumin flow for these 

 experiments is 8.5 mg/min. 



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with the intravascular mass was obtained from experi- 

 ments on unanesthetized, healthy greyhounds, infused 

 with 25 per cent albumin or bled, into which we in- 

 jected I 131 -labeled albumin and then determined the 

 albumin specific activities (218). We showed that 

 albumin specific activity curves can be altered by 

 changing the ratio of intravascular to extravascular 

 albumin masses in a manner predicted by a two- 

 compartment system. Increase of intravascular mass 

 (by infusion) relative to extravascular mass results in 

 a smaller initial disappearance of albumin specific 

 activity from the blood stream and a faster approach 

 to equilibrium. Decrease of intravascular albumin 

 mass relative to extravascular mass by bleeding shows 

 that 50 per cent of albumin replacement after hemor- 

 rhage appears to be accomplished within 24 hours. 

 Almost all this protein comes from the extravascular 

 compartment. Rapid anabolism accounts for the 

 replenishment of protein for the next 2 to 5 days, 

 during and after which there is a reduced catabolism 

 of the existing plasma albumin. Thus there are net 

 movements from the extravascular mass into plasma 

 when the equilibrium between intravascular and 

 extravascular masses is disturbed. 



Benson et al. (14) concluded that under stand- 

 ardized resting conditions a given tissue eliminates a 

 nearly constant amount of protein in its lymph per 

 unit of time and that the protein concentration in the 

 lymph from the intestine or liver of the rat varies 

 inversely with the volume of lymph flow. The concen- 

 trations of protein fractions in rabbit lymphs, and the 

 rates of exchange of radioiodinated human serum 



albumin between plasma and lymph which they ob- 

 served, suggested that the equilibration of plasma 

 proteins with lymph is rapid in the liver, intermediate 

 in the intestine, and slow in skeletal muscles. These 

 findings are consistent with our recent demonstration 

 (see figs. 2 and 3) of differences in blood capillary 

 permeability in different areas to macromolecules 

 (141) and the suggestion that there are several sets 

 of capillary pores of different sizes, large pores pre- 

 dominating in the liver, small pores in muscles, and 

 both size pores in the intestinal capillaries. Alter- 

 nately, the suggestion was made that cytopempsis or a 

 similar process may be involved. 



LYMPHATIC RETURN AND 

 BLOOD VOLUME REGULATION 



Lymph not only returns protein and other macro- 

 molecules from the extravascular to the vascular 

 system but also drains fluid representing the excess 

 of filtration over reabsorption through the capillary- 

 wall. As discussed later, the amount of lymph re- 

 turned to the blood stream via the thoracic duct 

 alone per 24 hours is roughly equivalent to the plasma 

 volume. It is thus obvious that the return of lymph 

 plays an essential role in the maintenance of the blood 

 volume level. However, little definitive data is avail- 

 able on this point. Courtice et al. (50) state that in 

 unpublished experiments on dogs anesthetized with 

 Nembutal "the rate of escape of fluid and protein 

 in lymph was equivalent to a daily loss of 60 per cent 



