ANATOMY

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

Detailed explanation-2: -The innermost lining of the veins and tunica intima contains this( semilunar) valve.

Detailed explanation-3: -Many veins, particularly those in the arms and legs, have one-way valves. Each valve consists of two flaps (cusps or leaflets) with edges that meet. Blood flowing toward the heart pushes the flaps open like a pair of one-way swinging doors.