AN ULTRASTRUCTURAL STUDY OF TRANSPORT PATHWAYS ACROSS RAT HEPATIC LYMPH VESSELS

Abstract

Hepatic lymph vessels in the rat were examined
by qualitative and quantitative analyses
in order to obtain data pertinent to the
mechanism of lymph formation. The ultrastructually
visible transport pathways across these
vessels appeared to be by way of intracytoplasmic
vesicles (89.6 micrometer mean
diameter) and normal channels (22.6 micrometer wide)
between endothelial cells. Three types of intercellular
contacts were seen, end-to-end,
overlapping, and interdigitating. Only one open
junction (>30 nm) was seen in 226 contacts examined.
Specialized junctional complexes, either
fasciae occludentes or fasciae adherentes, were
seen in 65% of the contacts. Approximately
one-third of the contacts had a dilatation along
part of their length separating the opposing endothelial
cells. Vesicles occupied 3.5% of the
endothelial cytoplasmic volume and were
distributed as follows: 40% opening onto or
touching the luminal membrane, 34% without
visible connection to either surface, 23% opening
onto or touching the abluminal membrane,
and less than 3% associated with membranes
forming intercellular contacts. It was concluded
that the mechanism of lymph formation in the
liver is similar to that in the kidney and different
from that in the dermis or diaphragm.