Placentan

Placentan is a term used in some contexts to refer to the placenta, the organ that links a developing fetus to the mother during pregnancy. In standard English usage, the term placenta is preferred. The placenta is a transient, highly vascular organ formed early in gestation and expelled after birth. It arises from fetal chorionic tissue and maternal decidual tissue.

Structure and development: The placenta is roughly disc-shaped and comprises fetal components—the chorionic plate and the villous tree—and maternal components—the decidua basalis and blood spaces. Maternal blood bathes the fetal villi in the intervillous spaces, allowing exchange without mixing the fetal and maternal blood. Formation begins around week 3–4 and continues to mature through mid-gestation. The placental barrier comprises trophoblast layers that regulate transfer of substances, while immune and endocrine functions become more pronounced as pregnancy progresses.

Function: The placenta supports the fetus through nutrient and gas exchange, waste removal, and endocrine functions. It produces hormones such as human chorionic gonadotropin (hCG), progesterone, estrogens, and human placental lactogen, which sustain pregnancy and influence maternal physiology. It also plays a role in immune tolerance of the fetus and metabolizes certain compounds, contributing to fetal protection and developmental signaling.

Clinical notes: Placentation patterns vary among mammals; in humans the placenta is of the hemochorial type, with maternal blood in direct contact with the chorion. Common placental problems include placenta previa, placenta accreta, placental abruption, and placental insufficiency, which can impact fetal growth. Monitoring includes ultrasound assessment and maternal blood tests to evaluate placental function and fetal well-being.