Electron microscopy of cytotrophoblast cell (human placenta, early pregnancy)

Below a single electron-light cytotrophoblast cell (CTC or Langhans cell, 1) covered by a syncytiotrophoblast cell (STC, 2) with two nuclei. A continuous basal lamina (3) separates the CTC and STC from the embryonic connective tissue. The CTC appears as a blast-like cell with a large electron-light nucleus in a relatively small cytoplasm studded with few profiles of endoplasmic reticulum, free polysomes, some glycogen particles and mitochondria as well as several electron-dense lysosomal structures. Small arrows indicate desmosomal contacts between the CTC and STC. CTCs proliferate by mitosis and eventually fuse and differentiate into postmitotic STCs which are in direct contact with maternal blood and proteins. The basal side of the STC (shown here with two nuclei) is stuffed with slightly dilated profiles of endoplasmic reticulum, numerous electron-dense lysosomes and few lipid droplets (steroidgenesis in the scope of the luteal-placental shift). At asterix (*) intervillous space.