Why are valves present in veins but not in arteries?
The main function of the valves in veins is to prevent back flow of blood.
Blood in the arteries, after being pumped by the heart, are under much higher pressure than blood in veins so there is no need for valves in arteries to prevent back flow.
Blood in veins is under much lower pressure as it is returning to the heart from the various organs and tissues and so has a risk of back flow if the valves are not present to prevent it.
Aside from preventing back flow of blood, valves in the veins aid in the return of blood from the extremities to the heart ( from feet and legs in particular).
Your heart is a strong muscle that can pump blood in spurts to all regions of your body right down to every capillary. The more difficult part is getting it back.
Rather than elastic arteries that carry away blood quickly and efficiently on the outbound route, we now have tiny capillaries that need to be cleared into increasingly larger veins to return the blood for cleaning in the liver and re-oxidizing in the lungs before the next departure.
Moreover, blood flows under high pressure in artery (BP is measured as pressure of blood exerted on wall of artery) but in veins the blood pressure is less than 10mm of Hg. To allow flow of blood back to heart, lumen inside vein is larger in diameter and to prevent backflow, series of valves are there.
Your veins have one-way valves in them to keep the blood moving, and in the right direction . You can help in this procedure simply by making movements. Try to avoid staying in one place or position for too long.
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