heart valves
a flap of tissue that prevants blood from flowing backward is
valves in the veins
Your heart keeps your blood "flowing"
Valves in the veins prevent the blood from flowing backward or from pooling.
your skin of course!
These are called valves.
The four heart valves.
The heart valves keep blood from flowing backward. This increases the efficiency of the pumping of the heart.
The flap of tissue that prevents blood from flowing backward is called a valve. Valves are found in veins and in the heart to ensure that blood flows in one direction and does not pool or backflow.
i think you mean bypass
veins have valves in them that prevent backflow