Fig. 4

View onto the installation of the primitive renal vesicle (pRV) in the fetal human kidney during advanced pregnancy by the optical microscope. The installation supports that the primitive renal vesicle exclusively forms at the proximal end of the pretubular aggregate (PTA) by arranging the polarized epithelial cells around a small lumen (+). Meanwhile, at the distal pole (DP) of the primitive renal vesicle, a partial separation (flash) takes place so it temporary remains connected with the overlying pretubular aggregate. At its medial aspect, the primitive renal vesicle shows an adhesion (white asterisks), which begins at the head (H) to continue up to upper conus (CO) of the CD ampulla (A). The mounted proximal pole (PP) of the primitive renal vesicle is yet part of a pendentive, which is formed by the perivascular interstitium of the perforating radiate artery (PRA) and the connecting tubule (CNT) at a previously formed nephron. C renal capsule, black asterisks clear interface