2.65 Describe the structure of arteries, veins and capillaries and understand their roles

ARTERIES
Arteries take the blood Away form the heart and to an organ (e.g.: lungs)
They have thick muscular walls and a small lumen, therefore, blood is under the highest pressure in them

VEINS
Take blood to the heart and away from an organ
They have a relatively thin wall and a large lumen, therefore blood is under the lowest pressure in them
They have watch pocket valves to prevent the blood from flowing backwards/in the wrong direction

CAPILLARIES
Where exchange is taken place
They have very thin walls (one cell thick) so that gas exchange can occur easily