Renal papillary morphology and intrarenal reflux in the young pig

Intrarenal reflux in piglets has been related to the morphology of individual renal papillae. These studies show that intrarenal reflux occurs only in the presence of the more extensively fused papillae found predominantly at the upper and lower poles of the kidney. These papillae each have a flattened or concave area cribrosa with large open papillary ducts which cannot be closed by a rise in intracalyceal pressure. In contrast intrarenal reflux never occurs into cone-shaped papillae seen most commonly in the mid-zone of the kidney, which have easily closed, oblique, slit-like papillary duct orifices. The significance of these findings in relation to the genesis of chronic pyelonephritic scarring is discussed.