A highly vascularized mammalian fetal-maternal organ and major site of transport of Oxygen, nutrients, and fetal Waste Products. It includes a fetal portion (Chorionic Villi) derived from Trophoblasts and a maternal portion (Decidua) derived from the uterine Endometrium. The placenta produces an array of steroid, protein and Peptide Hormones (Placental Hormones).