Rat kidney.
Histological section through the mid IS (detail of the previous section, at a higher magnification).
On the left is a half vascular bundle comprising arterial (descending) and venous (ascending) vasa recta, and on the center and right is an interbundle region. Numerous TALs (with thick dark wall) are visible, and between them, a few collecting ducts (with light wall and wide lumen) and thin descending limbs (of smaller diameter).
Brigitte Kaissling and Wilhelm Kriz,
Anatomisches Institut, Heidelberg, RFA