fish have a single circuit heart while mammals have two chambered heart but in both blood flows in two directions
human
Blood flow doesn't change direction. They always head for the same direction.
forward
Veins.
Valves control the flow of blood. Without them blood could flow backwards.--------------------------Yes, true. Valve would maintain one way traffic for blood right from the heart and to outside parts of the body and form outside to the heart.
NO
toward the heart from the lungs
Valvs
valves
yes :)
toward the heart if deoxegen
the valves