Placenta

About the Placenta

The placenta is a temporary organ that develops in the uterus during pregnancy, formed largely from tissues of the embryo and connected to the fetus by the umbilical cord. Fetal blood vessels branch into tree like chorionic villi that are bathed in maternal blood, so that oxygen, nutrients, and antibodies can pass to the fetus and carbon dioxide and waste products can pass back, without the two blood supplies mixing directly. The placenta is also an important endocrine organ, producing human chorionic gonadotropin, the hormone detected by pregnancy tests, as well as progesterone, estrogens, and human placental lactogen, which help maintain the pregnancy and adapt maternal metabolism. It provides a partial barrier against some infections and harmful substances, but many drugs, alcohol, and some infections can cross it. It is delivered after the baby as the afterbirth. Placental complications include placenta previa, in which it covers the cervix, placental abruption, in which it separates early, and placental insufficiency, and abnormal placental development is implicated in preeclampsia.