Blood vessels

 There are mainly three types of blood vessels in human body called Artery, Vein and Capillaries.

Artery:  Arteries carry blood from heart to other parts of body. Except pulmonary artery which passes blood from heart to lungs, carry pure blood. Arteries are formed by dividing aorta and further dividing of arteries arterioles are formed. Arterioles further divide into capillaries. Artery has thick wall and can hold large amount of blood pressure. Artery doesn’t have valve as 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.

Vein: The blood vessels which carry blood from body to heart are called vein. They carry impure blood which is collected in heart and sent to lungs for purification. To prevent backflow of impure blood there is valve on vein.

Capillaries: They are very thin blood vessels connecting blood flow on cell level. They supply nutrients, oxygen and minerals to cell and collect back west products.