Fig. 5

View onto the a early, b mid, and c late S-shaped body (SSB) in the fetal human kidney by optical microscopy. These extend along a CD ampulla (A) between its head (H), conus (CO), and neck (N). The medial aspect is separated from the CD ampulla by a vertical cleft (white arrows). At the distal pole, the connecting tubule (CNT) completes the physiological connection with the CD ampulla. The proximal pole (PP) is orientated towards the medulla. Here, the glomerulus develops including the podocytes (P) and Bowman’s capsule (BC). The proximal (PT), intermediate (IT), and distal (DT) tubule segments develop. a The outer cell layer at the proximal pole of an early S-shaped body forms the Bowman’s capsule. Separated by the urinary space in the overlying layer, the podocytes are found. The point of fold between both cell layers is at the deep lateral aspect of the S-shaped body. The transverse cleft (dashed white arrows) above is opening towards a vertically lining perforating radiate artery (short black arrow). b At the proximal pole of the mid S-shaped body, cells of the glomerulus differentiate. The Bowman’s capsule becomes flat and the podocytes develop a cobblestone-like appearance. The transverse cleft (dashed white arrow) above opens for vessel formation. At the urinary pole, the proximal tubule (PT) develops a brush border. In the intermediate and distal tubule segments, a lumen becomes visible. c The late S-shaped body extends the vertical length. At its proximal pole, the glomerulus is tilting. The Bowman’s capsule is flat and the urinary space is broadening. The facing podocytes increase in number. The cleft (dashed white arrows) at the basal aspect of podocytes changes direction from transverse to vertical. In its interior, the formation of capillaries is noticed. Its opening is orientated towards a vertically lining perforating radiate artery. In the mid and distal third of the S-shaped body, the tubule segments elongate by meandering. C renal capsule