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Department of Chemical and Biological Engineering, Tufts University, Medford, Massachusetts 02155
In this model of
oxygen transport in the renal medullary microcirculation, we predicted
that the net amount of oxygen reabsorbed from vasa recta into the
interstitium is on the order of 10
6 mmol/s, i.e.,
significantly lower than estimated medullary oxygen requirements based
on active sodium reabsorption. Our simulations confirmed a number of
experimental findings. Low medullary PO2 results from the countercurrent arrangement of vessels and an elevated
vasa recta permeability to oxygen, as well as high metabolic needs.
Diffusional shunting of oxygen between descending vasa recta (DVR) and
ascending vasa recta also explains why a 20-mmHg decrease in initial
PO2 at the corticomedullary junction only leads
to a small drop in papillary tip PO2 (<2 mmHg
with baseline parameter values). Conversely, small changes in the
consumption rate of DVR-supplied oxygen, in blood flow rate, in
hematocrit, or in capillary permeability to oxygen, beyond certain
values sharply reduce interstitial PO2. Without
erythrocytes, papillary tip PO2 cannot be
maintained above 10 mmHg, even when oxygen consumption is zero.
kidney; microcirculation; medullary interstitium; medullary hypoxia; mathematical model
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