Trophoblast
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Chorionic villi are part of a normal pregnancy. They are derived from the conceptus, i.e. NOT maternal.
Tumours arising from the trophoblast are dealt with in gestational trophoblastic disease.
Chorionic villi 101
- Maternal blood is around villi.
- Fetal blood (nucleated (fetal) RBCs) in the villi.
Basic histology
- Outer layer of villus: syncytiotrophoblasts.
- Beneath syncytiotrophoblast (and closer to fetus) cytotrophoblasts.
Chorionic villi 102
- Syncytiotrophoblasts (eosinophilic cytoplasm with vacuoles (contain hCG), multiple hyperchromatic nuclei).
- Large + many irreg. or lobular hyperchromatic nuclei.
- Eosinophilic vacuolated cytoplasm (contains hCG).
- Closest to mom - covers cytotrophoblast.[1]
- Cytotrophoblasts (polygonal shape, distinct borders, clear cytoplasm, in cords, single nucleus).
- Polygonal shaped cells in cords/masses.
- Distinct cell borders.
- Covered by syncytiobrophoblast[2] - closer to fetus than syncytiotrophoblasts.
- Clear cytoplasm.
- Single uniform nucleus.
Age of villi
Young villi
- Do not have blood vessels.
- No syncytial knots.
Old villi
- Blood vessels present and at the periphery of villus - contain nucleated (fetal) RBCs.
- Syncytial knots.