Veins are the blood vessels that carry blood towards the heart.
While arteries are thick and muscular, veins are very thin and contain almost no muscle. The walls of veins are so thin that you can see the blood inside of them.
The main function of veins is to carry blood from the body back to the heart. This blood is low in oxygen, depleted of nutrients, and loaded with waste products. If arteries are the supply train, veins can be thought of as the garbage trucks.
Veins are very stretchy, and can distend to several times their normal diameter. This ability lets them act as blood warehouses if the flow of blood slows down because of lowered heart rate or contracted arterioles. Because of this Property, they can help lower the impact of increasing blood pressure.
