Fig. 8

View onto the installation of the comma-shaped body (CSB) in the fetal human kidney during advanced pregnancy by the optical microscope. While the comma-shaped body is forming, the progenitor cell strand (white arrow heads), which lines to the proximal end of the pretubular aggregate (PTA), is dissolved by an unknown process during the proceeding installation. This causes that the neighboring peritubular interstitial pocket fuses with the perivascular interstitium at the neighboring perforating radiate artery (PRA). As a result, between the tubule anlage and the extending lateral fold, a cleft (white triangles) arises. It enables that the glomerulus defoliates at the proximal pole (PP) of the comma-shaped body. At the medial aspect, the narrow interstitial cleft (white circles) expands along the conus (CO) of the CD ampulla (A) towards the interior of the comma-shaped body. C renal capsule, black asterisks clear interface between the mesenchymal and epithelial progenitor cells in the nephrogenic niche, white asterisks adhesion, N neck of CD ampulla, CD collecting duct tubule DP distal pole, C renal capsule