Intervillous space with villi (human placenta, midpregnancy, cross-section)

Stain: Trichrome (Goldner). In the middle a thick stem villus (cross-sections of left artery (1) and right vein (2) of the umbilical circulation in the thick embryonic connective tissue) with ramifications into terminal villi (tertiary). Most tertiary villi of varying diameters contain capillaries and all villi are covered by multinucleated syncytiotrophoblast cell (STC, arrow 3). The layer of cytotrophoblasts is indicated by (arrow, 4). At several places reddish-stained fibrin-type fibrinoid accumulations associated with the villous surface are present (5).