Placenta

The placenta is a temporary organ that mediates exchange of nutrients, gases, and wastes between a developing fetus and its parent. It also produces hormones that support pregnancy.

Placental barrier: The tissue interface that separates maternal and fetal blood while allowing selective exchange. Its layered structure controls which substances cross between the two circulations.
Trophoblast: The outer cell layer of the early embryo that attaches to the uterine lining and contributes to the placenta. Trophoblast cells form the fetal portion of the placenta and invade maternal tissue.
Preeclampsia: A pregnancy disorder involving new hypertension after 20 weeks, often with signs of organ dysfunction. Abnormal placental development is implicated in many cases.
Yolk sac: An extraembryonic membrane that supports early development and has major nutritional roles in egg-laying animals. It supplies embryos in species that do not rely on a mammalian placenta for nourishment.
Maternal-fetal medicine: A medical specialty focused on health risks and complications during pregnancy. It evaluates conditions in which placental function affects both pregnant patient and fetus.
Umbilical cord: A flexible cord containing blood vessels that connects the fetus to the placenta. Its vessels carry fetal blood to and from the exchange surface.
Chorion: The outer fetal membrane that surrounds the embryo and develops chorionic villi. This membrane supplies the placenta’s fetal tissues and villous surface.
Placenta previa: A condition in which the placenta overlies or lies close to the cervix late in pregnancy. Placental location can obstruct vaginal birth and cause bleeding.
Marsupial placenta: A placenta in marsupials that supports fetal development, often for a shorter period than in eutherian mammals. Its limited gestational role differs from the prolonged exchange typical of many placental mammals.
Vertical transmission: The passage of an infectious agent from parent to offspring during pregnancy, birth, or breastfeeding. Some pathogens cross the placenta and infect the fetus before birth.

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