Question

why do veins have one way valves​

Answer 1

veins contain valves that ensure blood flows in only one direction. (Arteries don't require valves because pressure from the heart is so strong that blood is only able to flow in one direction.) Valves also help blood travel back to the heart against the force of gravity.

Answer 2

because they have to take blood towards the heart and to prevent it's back flow

hope it helps