PLACENTATION AND GESTATION

Endoderm forms the yolk sac inside the trophoblast eventually the yolk sac regresses into the gut Mesoderm forms double layer with trophoblast and becomes the chorion and the amnion Amnionic cavity forms a hydraulic protection around the embryo Evagination from the hind gut forms the allantois to collect liquid waste Chorion and allantois fuse to form the allantochorion which becomes the fetal portion of the placenta Endometrial cups in the mare

# * * * * * Indicates when the placenta takes over primary progesterone support # Indicates formation of accessory corpra lutea

Types of Placental Development Diffuse - Horse, Pig Zonary - dogs, cats Discoid - rodents, primates Cotyledonary - ruminants Fetal cotyledon Maternal caruncle Binucleate giant cells migrate from the fetal side to the maternal side probably responsible for transporting placental lactogen

Classification based on cellular associations Epitheliochorial - Horses, Pigs, (Ruminants) Syndesmochoria - Ruminantsl Endotheliochorial - Dogs, Cats Hemochorial - Rodents, Primates Hemoendothelial - Some Rodents

# * * * * * Indicates when the placenta takes over primary progesterone support # Indicates formation of accessory corpra lutea