Placenta

Abstract

The placenta is a complex organ with multiple fetal and maternal components, which respond differently to insults such as infection or ischemia. The gestational sac begins as a spherical structure, with the fetus surrounded by an amnion, a chorion, and placental villi. One surface of the gestational sac implants into the endometrium and becomes the placenta; the villi on the opposite surface degenerate. When you look at placental slides, you can see the layers of the amnion and chorion, both in the membrane section and on the fetal surface. In both locations, amnion is on the fetal side and chorion on the maternal side. The villi are fetal structures; they grow downward from the fetal surface in a branching architecture, like the roots of a tree. Vessels and cells inside the villi are fetal. There should not be any maternal vessels in the placenta itself. The spiral arteries of the decidua (endometrium), invaded and opened by trophoblastic cells, spray maternal blood into the space between the villi. This chapter outlines a systemic approach to the placenta intended to identify the most common pathologies which may come to a general surgical pathologist.