The blood-brain barrier is a protective barrier in the brain that prevents harmful substances in the blood from entering the brain tissue. It is made up of tightly packed cells that line the blood vessels in the brain, and it allows only certain substances, such as oxygen and glucose, to pass through.
The fetal-placental barrier is a protective barrier that separates the fetal blood supply from the maternal blood supply during pregnancy. It is made up of a number of layers, including the placenta and the fetal membranes, and it helps to protect the developing fetus from harmful substances that may be present in the mother's blood. The barrier also allows for the exchange of nutrients, oxygen, and waste products between the fetus and the mother.