placentomes

Placentomes are discrete placental structures found in the cotyledonary placenta of certain mammals, most notably ruminants such as cattle, sheep, goats, and deer. They are the functional sites where maternal and fetal tissues come into contact to allow nutrient and gas exchange during pregnancy. Each placentome consists of a fetal cotyledon attached to a maternal caruncle, and they are arranged along the uterine surface in a patchwork pattern rather than as a single diffuse interface.

During gestation, placentomes form at sites where the fetal cotyledon fuses with the maternal caruncle, and their number and size typically increase as pregnancy progresses. Their external shape may be described as convex or concave, reflecting differences in the relative growth of fetal versus maternal tissues at the interface.

In cattle and other ruminants, the placenta is of the synepitheliochorial type, with fetal trophoblast cells forming binucleate cells that invade the maternal epithelium to create syncytial plaques. This arrangement allows exchange between maternal and fetal blood while preserving most maternal tissue integrity.

Clinical relevance: Placentome number, size, and appearance are used in veterinary practice to monitor placental development and fetal well-being during mid to late gestation. Ultrasound or manual palpation can assess placentomes, and abnormally large, small, or irregular placentomes can indicate placental insufficiency, fetal growth restriction, or abortion risk.

Placentomes are a key feature of cotyledonary placentation in ruminants and are distinct from placental structures found in other mammals.