Red cell and albumin circulations in the ileum

¹ Department of Physiology, University of Texas Medical School, Galveston, Texas

A method for investigating the compartments in an organ through which labeled materials circulate has recently been refined. This was applied to the ileum. Radioactive red cells left the tissue as if they were circulating through a single compartment: its turnover time was 9.5 sec and its apparent volume was 3.7 ml/100 g tissue. But radioactive albumin left the tissue as if it was circulating through three compartments. They lay in parallel. Their turnover times were 10.3, 42, and 370 sec, and their apparent volumes were 6.7, 3.7, and 3.8 ml/100 g. Because the time constants for the red cell compartment and the first albumin compartment are the same, it is thought that this is an intravascular compartment. Its hematocrit ratio is the same as that in systemic blood, indicating that blood flows through the compartment in the same way that it flows through large vessels. The other two albumin compartments, neither of which is penetrated by red cells, are postulated to be interstitial and/or lymphatic-lacteal in nature. This hypothesis is harmonious with the porous character, recently revealed by electron microscopy, of the membranes in these regions.