Placenta; compared anatomy and histology Placenta: Anatomía e histología comparada

The placenta is an extraembryonic membrane of placental mammals, essential for embryo survival. It is formed by the most superficial zone of the endometrium and the chorion, associated with the yolk sac or allantois, depending on the species. The placenta provides gas and nutrient exchange between mother and fetus, secretes hormones and has immunosuppressive properties. There are different criteria to classify the placenta; i. e. according to the distribution of the chorionic villi of the placenta: diffuse, cotyledonary, zonaria and discoidal; according to the histological characteristics of the placenta: epitheliochorial, syndesmochorial, endotheliochorial and hemocorial