Investigating the nephron architecture between the outer and inner medulla of the rat kidney

Abstract

The rat kidney consists of one renal pyramid which can be divided into three fundamental regions; the cortex, outer medulla, and inner medulla. Nephrons are organized throughout these three regions in a highly organized fashion. The focus of this study is to identify the architectural relationships between the descending (DVR) and ascending vasa recta (AVR), the ascending thin limbs (ATLs), and collecting ducts (CDs) between the inner and outer medulla. Architectural relationships were identified through digital reconstructions of nephrons and vessels observed in images of physical and optical sections prepared at 1 to 5μm intervals. The short long loops of Henle have glomeruli positioned in the cortex above the border with the outer medulla. Their loops of Henle descend into the inner medulla, looping bends predominantly within the interior of CD clusters. The four to six AVR arranged symmetrically around each inner medullary CD form similar arrangements with outer medullary CDs. Interstitial spaces are formed adjacent to CDs in outer medulla and appear to be associated with thick ascending limbs of Henle. These relationships may contribute to the differences between the inner and outer medullary concentrating mechanisms. (NIH DK16294)