chorionic floating villus

A chorionic floating villus is a type of chorionic villus that is not attached to the placental basal plate or maternal uterine wall. Instead, it is freely suspended and immersed in the maternal blood that fills the intervillous space of the placenta.

Chorionic floating villi are the primary sites of maternal-fetal exchange in the placenta. Because they are bathed in maternal blood, their large collective surface area and thin exchange membrane allow efficient transfer of oxygen, glucose, amino acids, fatty acids, and vitamins from mother to fetus, as well as elimination of carbon dioxide and waste products from fetal blood.

Floating villi are immersed in maternal intervillous blood and serve primarily for exchange, while anchoring villi are attached to the maternal uterine wall and serve primarily for structural support and trophoblast invasion. The trophoblast covering of floating villi is maintained as an intact syncytiotrophoblast layer, whereas the tip of anchoring villi transitions to a cytotrophoblast cell column.

Floating villi include mesenchymal villi (earliest type, precursors of other types), immature intermediate villi, mature intermediate villi, and terminal villi. Terminal villi are the final branches of the floating villous tree and are the most specialized for exchange, characterized by sinusoidal capillary dilations and thin vasculosyncytial membranes.

Various conditions can affect floating villi. Perivillous fibrin deposition involves accumulation of fibrin around floating villi, potentially reducing the exchange surface. Villitis of unknown etiology is an inflammatory condition in which maternal immune cells infiltrate the stroma of floating villi, impairing placental function. Increased syncytial knots (aggregates of syncytiotrophoblast nuclei) in floating villi are a marker of villous hypoxia and placental aging.