Arteries

• It is the job of the arterial system to carry blood away from the heart. Arteries are equipped with thick walls, smooth muscle and very elasticized tissue. Each time blood surges from ventricle, arteries expand and those elastic walls shrink between the beats of the heart, which acts to pump blood in a steady flow through the vessels, which are smaller than arteries.
  
  

Capillaries

• Capillaries are very small blood vessels and it is their job to pick up carbon dioxide, nutrients, gas, hormones and waste from the blood cells and drain them into larger vessels called venules. The venules then empty into even larger vessels called veins. Capillaries are incredibly tiny and numerous--the average human body actually contains about 50,000 miles of capillaries.
  
  

Veins

• Veins are the method by which blood can return back to the heart through the path of least resistance. Vein walls are thinner, contain less muscle tissue and expand more freely than arteries. The natural assumption would be that contraction of the veins would initially send blood away from the heart before sending it to the heart, but in fact veins come equipped with one-way valves to prevent this occurrence and make sure that the blood goes only toward the heart.