Fig. 6

View onto the installation of the extending renal vesicle (exRV) in the fetal human kidney during advanced pregnancy by the optical microscope. Its distal pole (DP) with the establishing connecting tubule (CNT) is positioned next to the proximal end of the pretubular aggregate (PTA). Thereby, a pendentive is here formed by the subcapsular interstitium and the perivascular interstitium of a perforating radiate artery (PRA). At the same time, the connecting tubule invades the epithelium of the CD ampulla (A) between its head (H) and conus (CO). While the tubule anlage of the extending renal vesicle vertically elongates, the lateral aspect of the extending renal vesicle is still connected via a progenitor cell strand (white arrow heads) with the overlying pretubular aggregate. At the lateral fold, the formation of a cleft (white triangle) prepares the connection between the arising glomerular tuft and the vertically lining perforating radiate artery (PRA). At the medial aspect of the extending renal vesicle, the adhesion to the CD ampulla alters to a narrow interstitial cleft (white circles). C renal capsule, + lumen, black asterisks clear interface between the nephrogenic mesenchymal and epithelial progenitor cells in the niche, white asterisks adhesion, N neck of CD ampulla, CD collecting duct tubule, DP distal pole, PP proximal pole, C renal capsule