MICROANATOMY

Detailed explanation-1: -Veins have valves to prevent the backflow of blood because the blood in veins flow .

Detailed explanation-2: -If gravity or muscle contractions try to pull the blood backward or if blood begins to back up in a vein, the flaps are pushed closed, so the blood does not flow backward. Thus, valves help the return of blood to the heart-by opening when the blood flows toward the heart and closing when blood might flow backward.

Detailed explanation-3: -Most veins have valves that open and close. The valves control blood flow and keep your blood flowing in one direction. About 75% of your blood is in your veins.