Download 7-8

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.
• 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 Placenta
Common Examples
Diffuse, epitheliochorial
Horses and pigs
Cotyledonary, epitheliochorial
Ruminants (cattle, sheep, goats,
deer)
Zonary, endotheliochorial
Carnivores (dog, cat, ferret)
Discoid, hemochorial
Humans, apes, monkeys and rodents