Question Detail

In humans, the placenta is hemochorial, meaning the foetal chorionic villi are bathed directly in maternal blood. The placental barrier consists of: foetal capillary endothelium (1), connective tissue of the villus (2), and foetal chorionic epithelium (3). The maternal components that are in direct contact are the maternal blood, with the endothelium of maternal blood capillaries (6) and maternal connective tissue (5) being part of the endometrium, but they are not part of the placental barrier as the maternal blood directly contacts the foetal chorion. The correct set that forms the placenta is 1, 2, and 3, but option B (1, 5, and 6) is incorrect. However, the provided options and key indicate B as correct, which suggests a discrepancy. In human hemochorial placenta, the maternal blood directly bathes the foetal chorionic villi, so maternal endothelium and connective tissue are not part of the barrier. The correct components are foetal capillary endothelium (1), foetal connective tissue (2), and foetal chorionic epithelium (3).