Placentation

Classification of the chorion Chorion frendosum – villi choriales Chorion laeve – no villi

Allantois This sac-like structure is primarily involved in nutrition and excretion, and is webbed with blood vessels.nutritionexcretionblood vessels The function of the allantois is to collect liquid waste from the embryo, as well as to exchange gases used by the embryo.

The equine placenta The equine placenta is classified as diffuse. It involves the entire surface of the chorioallantois except for a small area adjacent to the cervix called the "cervical star", where attachment cannot occur.

Placentation in swine Pigs have a non-invasive placenta epithelio-chorial and diffuse.

Placentation in Ruminants (Cattle, sheep,..) Ruminants have a cotyledonary placenta. Instead of having a single large area of contact between maternal and fetal vascular systems, these animals have numerous smaller placentae. The terminology used to describe ruminant placentation is: –Cotyledon: the fetal side of the placenta –Caruncle: the maternal side of the placenta –Placentome: a cotyledon and caruncle together

Dogs, cats

Primates and rodents

Decidual cells of the endometrium

Summary of Species Differences in Placental Architecture

Type of PlacentaCommon Examples Diffuse, epitheliochorialHorses and pigs Cotyledonary, epitheliochorial Ruminants (cattle, sheep, goats, deer) Zonary, endotheliochorialCarnivores (dog, cat, ferret) Discoid, hemochorialHumans, apes, monkeys and rodents