AN INTEGRATED LIGHT AND ELECTRON MICROSCOPIC STUDY ON THE EXISTENCE OF INTRAMEDULLARY LYMPHATICS IN THE DOG KIDNEY

Abstract

The existence of intramedullary lymphatics was
investigated in canine kidneys by two detailed morphological
approaches. The first used a combined
light and electron microscopic analysis of medullary
tissue fixed in vivo and obtained from animals with
dilated as well as freely-flowing intrarenal lymphatics.
Examination of 100 vascular bundles and 100
interbundle areas from 90 medullary tissue strips
elicited only one strip containing lymphatic vessels.
These lymphatics, in a vascular bundle, were confumed
ultrastructurally and were followed in serial
one micron sections which revealed their course to
be immediately adjacent to or within the arcuate
region. The dearth of medullary lymphatics was in
marked contrast to the existence of cortical lymphatics
found in similarly processed tissue. By the
second approach sections of arcuate lymphatics
were examined for medullary tributaries. In serial
sections from 60 tissue blocks arcuate lymphatics
received only cortical tributaries. Reconstruction
diagrams made from 8 blocks showed 14 tributaries
from the cortex and none from the medulla. It was
concluded from this study that an intramedullary
system of lymphatics does not exist within the dog
kidney. It is proposed that a medullary contribution
to renal lymph occurs by movement of fluid through
the medullary interstitium to lymphatics associated
with arcuate or possibly interlobar blood vessels.