Human placenta. Coloured scanning electron micrograph (SEM) of villi in the healthy placenta of a woman at the time of childbirth. The placenta is the temporary organ that connects a developing foetus to its mother. The villi, projections of foetal tissue into the maternal part of the placenta, are packed with blood vessels, allowing the foetus' blood supply to come very close to the mother's blood. This allows the exchange of gases, nutrients and waste with the mother's blood, as the foetus cannot breathe, feed or excrete while in the womb.