Development of Function in the Metanephric Kidney

This chapter focuses on characterizing the normal functional development of the metanephric kidney. Although the bulk of the fundamental knowledge about these processes derives from investigations in animal models, available data from studies in the human fetus and neonate are also discussed in the chapter. In animal models used to study ontogeny of renal function, nephronogenesis is complete before term birth in sheep and guinea pig. The fetal sheep provides an excellent model of human nephronogenesis as its program of renal development closely parallels that of the human. Nephronogenesis continues for ~1 week after term birth in rat and mouse and ~2 weeks in rabbit and dog. Thus, functional analyses of the differentiating kidney in these latter species are complicated by the concurrent presence of nephrons in diverse stages of differentiation. Furthermore, physiologic, biochemical, and enzymatic maturation of newly formed nephrons in all species may lag behind anatomic maturation by weeks or months. A comparison of the developmental changes in renal function among various species is best considered not as pre- or postnatal events but in terms of their relationship to the completion of nephrogenesis.