Gross specimen of a normal placenta. The placenta surrounds the embryo in the womb. Its main function is to provide the embryo with nourishment, eliminate wastes and to exchange respiratory gasses. This is able to occur as the maternal and foetal blood vessels are in very close proximity in the placental chorion. The placenta also acts as a gland, secreting hormones that maintain pregnancy. The placenta, the umbilical cord and associated membranes are expelled up to a few hours after birth of the child.