what is vein?
Veins are thin-walled structures inside of which a set of valves keeps blood in the body flowing in one direction. The heart pumps oxygen-rich blood to the body's tissues through thicker-walled arteries; the veins return that blood to the heart.
Veins are thin-walled structures inside of which a set of valves keeps blood in the body flowing in one direction. The heart pumps oxygen-rich blood to the body's tissues through thicker-walled arteries; the veins return that blood to the heart.
