Functional segmentation of the mammalian nephron.

Although each of the major experimental techniques applied to the study of renal physiology has provided its fair share of new information, the technique of in vitro microperfusion of nephron segments is notable for two major contributions. First, it has supplied a more direct and controlled means of studying epithelial transport processes, some of which already have helped us to understand certain aspects of kidney function and others of which have yet to find their application in unraveling the mysteries of the kidney. Second, in the process of delineating these transport characteristics, it has served to emphasize the epithelial specialization present in the kidney, providing functional counterparts to the already recognized anatomic heterogeneity present in the kidney. In this second role microperfusion has spawned the application of biochemical analysis of the hormonal responses of various nephron segments and contributed to the impetus for work in culturing the various cell types present in each nephron segment. This review outlines the functional characteristics of the 11 major segments of the nephron, incorporating what has been learned from some of the biochemical work on hormone response and correlating the latter with transport events.