1. 1. ARTERIES Blood vessels that take blood away from the heart are known as ARTERIES. 2. VEINS Blood vessels that take blood back to the heart are known as VEINS. aa Remember, arteries (away) inin Remember, veins (into the heart) Three broad types of vessels

2. 3. arteriesveins Finally, if arteries take blood away from the heart and veins take blood back to the heart, when does an artery turn into a vein? Well, our third type of blood vessel links the two. We find it present where an artery finishes and a vein is about to begin. CAPILLARY. This third type of blood vessel is known as a CAPILLARY. and in between…

3. Artery cross-section small lumen thick muscle and elastic fibres

4. The small size of the lumen means that blood will be under high pressure. The thick fibrous wall strengthens the artery. Arteriole pressure Imagine using a water hose and putting your thumb half over the open end. The water is released under higher pressure and it flows faster.

5. The blood flowing through an artery will be under high pressure and moving extremely fast. There is no chance that the blood will turn around and start travelling in the opposite direction. no valves Therefore, there are no valves present in arteries. Blood flow in arteries

6. large lumen thin muscle and elastic fibres Veins: cross-section

7. The lumen of a vein is much thicker than the wall that surrounds it. There is less of a need to maintain a high pressure. The walls still contain elastic and muscle but there is far less present compared to the artery. You will appreciate that the blood is flowing far less quickly through veins compared to arteries. Walls of veins

8. leg Q. What would happen if blood loses so much energy that it stops and turns around? vein This situation could arise where blood is flowing against gravity. However, there is a solution to this problem and it comes in two parts. Preventing backflow Normal direction of blood flow gravity

9. 1.Firstly, veins have valves which act to stop the blood from going in the wrong direction. (These valves are similar to those found in the heart) valves open blood valves close Valves

10. These vessels link arteries with veins. They are found all over the body and are essential for the exchange of materials between the blood and other body cells. arteryvein capillaries Capillaries: role and position

11. very narrow lumen The wall of a capillary is only one cell thick! Capillaries are so small that they can only be seen using a microscope. capillary bed A collection of capillaries is known as a capillary bed. Capillary bed body cell

12. Vessel test. Part 1

13. Vessel test. Part 2

14. Multiple-choice quiz