13.2 THE BLOODSTREAM
Arteries take blood to the lungs to become oxygenated, then they take oxygenated blood around the body. Arteries have thick walls composed largely of muscle and elastic tissue. When the muscle contracts, it constricts the flow of blood through the artery. This is how blood flow to different organs are controlled The elastic tissue allows the artery to expand when blood is forced into it.
Veins take deoxygenated blood back to the heart. They have much thinner walls than arteries do but they have a bigger lumin. The blood flowing through the veins is of a very low pressure as it is not being pumped much by the heart. They have valves to prevent back flow of blood, particularly in the legs.
Capillaries are tiny blood vessels. They are so narrow that only one red blood cell is able to pass through them and they have very thin walls so gases can diffuse out of the capillaries.They are situated throughout organs.
Red Blood Cells
They are very specialised cells that…