Rabbit kidney.
Venous vessels (Microfil injected retrogradally through the renal vein).
Longitudinal section showing the cortex and outer medulla.
The radially oriented cortical veins and peritubular capillaries that merge into them are visible in the cortex. In the medulla, venous vasa recta ascend from the deeper medulla towards the cortico-medullary border where they will merge into the arcuate veins).
Note the high density of vasa recta in the upper part of the medulla closest to the deep cortex, where the late parts of the pars recta of all nephrons run. This setting (ascending vessels and descending tubules) should favor secretion of solutes from blood to tubular fluid.
L. Bankir, N. Bouby, MM Trinh-Trang-Tan.
In Nephrology; Proc. IXth Int. Cong. Nephrol. Los Angeles (RR Robinson Editor) Springer Verlag, 1984, pp 84-106