1. Arteries carry blood away from the heart and have to tolerate the force exerted by the blood which is under high presssure exerted by the heart. The walls of the arteries are thick and elastic.
2. The veins collect the blood from different parts of the body and bring it back to the heart. They do not need thick walls as blood is no longer under high pressure; instead they have valves to prevent the backward flow of blood.
3. On reaching the tissues arteries divide and redivide into smaller and smaller vessels called capillaries to bring the blood in contact with individual cells.
4. Exchange of material between the blood and the surrounding cells takes place across the thin walls of the capillaries.
5. The capillaries join together to form veins which take the blood away from the organ but towards the heart.
2. The veins collect the blood from different parts of the body and bring it back to the heart. They do not need thick walls as blood is no longer under high pressure; instead they have valves to prevent the backward flow of blood.
3. On reaching the tissues arteries divide and redivide into smaller and smaller vessels called capillaries to bring the blood in contact with individual cells.
4. Exchange of material between the blood and the surrounding cells takes place across the thin walls of the capillaries.
5. The capillaries join together to form veins which take the blood away from the organ but towards the heart.
