The postnatal development of the XXXX kidney, with special reference to the chemodifferentiation of the proximal tubule.

@entity35 @entity69167 @entity227
New nephron anlages appear in the renal cortex up to the 4th @entity227 ( @entity227 ). The last anlages to be formed develop into functional nephrons by @entity227 10, and the cortex appears mature at @entity227 12 after formation of the cortex corticis. The renal medulla develops by the longitudinal growth of loops of Henle and collecting ducts. The immature medulla cannot be divided into different zones and corresponds structurally to the later inner stripe of the outer zone. The inner zone is formed by @entity227 8, and the outer stripe of the outer zone by @entity227 12. The renal medulla is mature at @entity227 21. From the start of its development, the renal proximal tubule consists of the pars convoluta and pars recta. In both parts the formation of the brush border is accompanied by the simultaneous appearance of brush border enzymes (alkaline phosphatase, gamma-glutamyltranspeptidase, dipeptidylaminopeptidase IV) and lysosomal enzymes (acid phosphatase, acid beta-galactosidase, @entity69167 ) over the full length of the proximal tubule. During the course of proximal tubule maturation, however, the lysosomal enzyme activities decline in the pass convoluta (with constant brush border enzyme activities), while the brush border enzyme activities increase in the pars recta (with constant lysosomal enzyme activities). The two parts further differ in that they exhibit different lysosomal patterns from the outset, the pars convoluta containing numerous large, highly enzyme-active lysosomes arranged in groups, and the pars recta containing only a few very small lysosomes with low enzyme activity. Thus, even in the newborn @entity35 , the lysosomal pattern of the pars recta already corresponds to that of the mature S3 segment. The S1 and S2 segments of the pars convoluta first differentiate between @entity227 10 and 21, as the groups of large lysosomes are progressively broken up and the extent of the lysosomal apparatus is diminished, this proceeding in a retrograde direction from the end of the immature pars convoluta.
