Chorionic villi are tiny, finger-like projections that develop from the outer layer of the placenta during pregnancy. They play a crucial role in the exchange of nutrients and waste between the mother and the growing fetus. These structures increase the surface area for absorption and help anchor the placenta to the uterine wall. The chorionic villi contain blood vessels that connect to the fetus's circulatory system, allowing for the transfer of oxygen and essential nutrients. They also help in the production of hormones that support pregnancy. Overall, chorionic villi are vital for fetal development and maternal health.