Fig. 5

a–l Sketches almost true to scale illustrate the interstitial situation at the developing nephron in the fetal human kidney during advanced pregnancy. Depicted are the configuration of the interstitium at the a pretubular aggregate (PTA), the b site of the mesenchymal-to-epithelial transition, and the c primitive renal vesicle (RV). Inserts, C renal capsule, SP stromal progenitor cells, NP nephrogenic progenitor cells, DE distal end, PE proximal end, PTA pretubular aggregate, PRA/black arrow perforating radiate artery, black asterisks interface, white asterisk adhesion, CNT connecting tubule of a previously developed nephron, A collecting duct (CD) ampulla, T tip, H head, CO conus, N neck, flash partial separation of RV from PTA, + lumen, C renal capsule, NZ nephrogenic zone, MZ maturation zone. Demonstrated is further the extension of the interstitium at the d mature, e extending, and f extended renal vesicles (RV). DP distal pole, PP proximal pole, TA tubule anlage with the future connecting tubule (CNT) of the presently developing nephron, arrow head progenitor cell strand between RV and PTA. Shown is also the interstitial configuration at the g early, h mid, and (i) late comma-shaped bodies (CSB). DT distal tubule, IT intermediate tubule, PT proximal tubule, P future podocytes, BC presumptive Bowman’s capsule. Finally, depicted is the extension of the interstitium at the j early, k mid, and l late S-shaped bodies (SSB) including the defoliation of the glomerulus at the proximal pole and the physiological connection of the CNT with the CD ampulla. Light blue/zigzag, interstitium within the renal capsule. Dark blue/vertical double arrow, interstitium between the inner side of the renal capsule and the tip of a CD ampulla. Yellow line with crosses, subcapsular interstitium. White boxes with red line, perivascular interstitium at the perforating radiate artery. Black line, peritubular interstitium at the connecting tubule. White boxes with red line and arrowhead, interstitial cleft at the deep lateral aspect between the tubule anlage and the defoliating glomerulus during formation of the comma- and S-shaped bodies. Dashed black line, oblique interstitial cleft between the tubule anlage and the progenitor cell strand, which connects the distal pole of the renal vesicles with the proximal end of the pretubular aggregate. White arrow, vertical narrow interstitial cleft between the CD ampulla and the medial aspect of the shaping nephron