Question

why veins have valves but not in arteris

Answer 1

Unlike arteries,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

this is not the question of social. it is of bio but I will answer

veins have valves because ,so that blood can flow in one direction only(uniderictional flow) but arteries do not because the blood in them flow in both directions ( upward as well as downward)

hope it is clear ...
by Roshan..