placentación

Placentation refers to the formation and development of the placenta, an organ unique to female mammals that facilitates nutrient and gas exchange between the mother and the fetus during pregnancy. The placenta is a temporary organ that develops from both fetal and maternal tissues. Its primary role is to provide oxygen and nutrients to the developing fetus while removing waste products.

The process of placentation begins shortly after fertilization when the developing embryo implants into the uterine wall. Fetal tissues, specifically the trophoblast, invade the endometrium, the lining of the uterus. Maternal blood vessels then grow into the developing placental structure. This creates a vascular connection that allows for the transfer of substances.

Different types of placentation exist, categorized based on the relationship between the fetal and maternal tissues. In epitheliochorial placentation, all layers of the uterine wall remain intact, and exchange occurs across the trophoblast, uterine epithelium, and connective tissue. In endothelialchorial placentation, the uterine epithelium is eroded, and the fetal trophoblast is in direct contact with the endothelium of maternal capillaries. In hemochorial placentation, the trophoblast is in direct contact with maternal blood. This latter type is found in humans and primates and is considered the most efficient in terms of nutrient and gas transfer.

The placenta also produces hormones essential for maintaining pregnancy, such as progesterone and estrogen. It acts as a barrier, preventing the mixing of maternal and fetal blood directly, though some antibodies can cross, providing passive immunity to the fetus. After birth, the placenta is expelled from the uterus as the afterbirth.