BIOLOGY Volume 3 - A Guide to General Biology - 2004

21. REPRODUCTION

21.8. Human Sexual Reproduction

21.8.8. The Placenta

Mechanisms of Substance absorption across the Placenta

The surface membranes of the Cells within the chorionic villi walls form microvilli, which increase the surface area available for the exchange of substances via diffusion, Facilitated Diffusion, Active Transport, and pinocytosis. These cells contain numerous Cell/35.html">Mitochondria that supply the energy required for active transport and pinocytosis. The surface membranes of the cells possess carrier molecules, enabling the villi to absorb various substances through active transport. Numerous small vesicles found within the villus cells indicate the uptake of substances from the Blood via pinocytosis (see section 5.9.8).



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