Carry blood out of the heart. Vessels become more numerous but smaller as they branch and take blood to different parts of the body. The muscle can contract just as skeletal muscle does, and when it does so, it may stop blood flow in that vessel. This can divert flow from one part of the body and send it to another.
Pressure is high in large arteries, but decreases as they approach the capillaries.
Capillaries are about the size of a RBC, and these pass through single file. Pressure is 35 at arterial end and 15 at venous end. Blood enters from capillaries at 15 mm and pressure drops to zero at the heart. The many veins coalesce into one big one that takes blood back to the heart. Veins are thin-walled and can expand more than arteries.