Why are valves present in veins but not in arteries?

Answer 1

To help bring the blood back against gravity.

Answer 2

Because the heart can exert more pressure when contracting (systole) than when expanding (diastole). So while the heart can push blood out into the body, it needs help to get it back from the capillaries so it can repeat the cycle.

The valves in the veins allow muscular contractions to assist the diastole, especially from the legs. It takes even more assistance to get the blood back up from the legs because it's fighting gravity as well as pressure.

Note that a side effect of this is that it can be quite dangerous to stop exercising suddenly, because the heart is pounding hard and relying on the muscles to help push the blood back. This is why a cool-down after vigorous exercise is necessary.

Answer 3

Arteries are pressurized by your heart and therefore the blood never goes backward. In veins, there is slight pressure, but not enough to hold blood. There are one-way valves in your veins to keep blood from going backwards, especially when flowing up your body, like your feet and legs.

Answer 4

Remember from the heart, its mostly down hill. Veins are all Upstream hence the valves.

Else, your blood would stay near you feet with no way of getting back to the lungs for some more O2.

Answer 5

because if the veins didnt have velve the blood would be affected by graviyt and would keep going up the vein tube. the valve stops the blood