A histologic description of certain epithelial and vascular structures in the kidney of the normal rat

The cytology of the whole length of the collecting tubule of the rat kidney was studied by light microscopy. The tubule may be subdivided into four successive segments on the basis of the types of epithelial cells that form its lining. The morphology of other epithelial and vascular structures in the renal medulla and papilla was also studied. In fixed histologic specimens, morphologic characteristics of capillaries near the apex of the papilla and in retia mirabilia of the outer portion of the medulla suggest that their plasma is relatively concentrated in the living rat. First, plasma in capillaries of both regions stains deeply with certain histologic dyes. Second, in many specimens erythrocytes in capillaries near the apex of the papilla appear crenated. The significance of the morphologic findings is discussed with regard to current hypotheses concerning the physiologic function of the collecting tubule and other epithelial and vascular structures in the medulla and papilla.