What is placenta? Mention its role during pregnancy?

Placenta is a special tissue between developing foetus and uterine wall through which the foetus gets all the requirements from the mother's body. It is a disc-like structure which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue and blood spaces on the mother’s side. The blood spaces surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta.