When and where do chorionic villi appear in humans ? State their function.

Explanation

After implantation , finger-like projections appear on the trophoblast called chorionic villi. The chorionic villi and uterine tissue become inter digitated with each other and jointly form a structural and functional unit between developing embryo (foetus) and maternal body called placenta.The placenta facilitates the supply of oxygen , antibodies , hormones and nutrients to the embryo. It also helps in the elimination of carbon dioxide and excretory wastes from foetus.