What is the flap of tissue that prevents backflow?

The flap of tissue that prevents backflow is called a valve. In the cardiovascular system, valves in the heart and veins ensure that blood flows in one direction, preventing it from returning to the previous chamber or area. In the digestive system, the lower esophageal sphincter serves a similar purpose by preventing stomach contents from flowing back into the esophagus. Valves are crucial for maintaining proper circulation and function in various body systems.