Placenta is an organ that connects the developing foetus to the uterine wall for supporting pregnancy.
It is formed after implantation. Finger-like projections appear on the trophoblast called chorionic villi, which are surrounded by the uterine tissue and maternal blood. The chorionic villi and the uterine tissue become interdigitated with each other and jointly form a .structural and functional unit between foetus and maternal body, i.e. placenta.