Electron microscopy of tertiary villus (human placenta, midpregnancy)

In the left photograph (A) is shown part of a tertiary villus with the organelle-rich cytoplasm of a syncytiotrophoblast cell (STC, 1). Below a single electron-light linked cytotrophoblast cell (CTC or Langhans cell, 2) covered by the STC. A higher magnification of another CTC (right photograph) shows the basal cytoplasmic site and a relatively thick basal lamina (arrows). The embryonic connective tissue (B) contains electron-dense spots representing calcium deposition (3) close to the basal lamina as well as partly fused with a degenerative extracellular electron-dense vacuolar structure (3) (calcium deposits are frequently encountered in placentas of smokers). Packed bundles of collagen fibrils (4) are now visible in the embryonic compartment