There are three main types of blood vessels: arteries, veins, and capillaries. Arteries carry oxygenated blood away from the heart to tissues throughout the body. They have thick muscular walls and elastic tissue to withstand high blood pressure. Veins carry deoxygenated blood back to the heart and have thinner walls and valves to prevent backflow. Capillaries are the smallest blood vessels and form a network between arteries and veins in tissues, allowing for the exchange of water, oxygen, nutrients and waste.

1. Animal Transport Systems Blood Vessels

2. Blood Vessels There are three main types of blood vessels i/ Arteries ii/ Veins iii/ Capillaries

3. ARTERIES

4. ARTERIES ARTERIOLES

5. ARTERIES ARTERIOLES CAPILLARIES

6. ARTERIES ARTERIOLES CAPILLARIES VENULES

7. ARTERIES ARTERIOLES CAPILLARIES VENULES VEINS

8. Blood Vessels ARTERIES Carry blood away from the heart Thick muscular walls Lots of elastic tissue in wall Relatively small lumen Blood under high pressure Blood flow rapid Blood flows in pulses No valves

9. ARTERIES

10. ARTERIES artery outer layer

11. ARTERIES artery outer layer thick smooth muscle

12. ARTERIES artery outer layer thick smooth muscle elastic white fibrous tissue

13. ARTERIES artery outer layer thick smooth muscle elastic white fibrous tissue inner lining (endothelium)

14. Arteries The elastic tissue in the artery wall allows the vessel to ‘give’ as blood surges through. So, the artery wall first stretches as a result of the high blood pressure, before an elastic recoil of the wall pushes the blood on its way. This swelling can be felt as a pulse where arteries travel near the skin surface.

16. Blood Vessels VEINS Carry blood back to the heart Thin muscular walls Little elastic tissue in the wall Relatively large lumen Blood under low pressure Blood flow is slow No pulse Valves prevent backflow of blood

17. Vein

18. Vein outer layer

19. Vein outer layer thin smooth muscle

20. Vein outer layer thin smooth muscle inner lining (endothelium)

21. Vein outer layer thin smooth muscle inner lining (endothelium) valve

22. VEINS How the semi-lunar valve works in a vein: The blood has just enough pressure to force the valve open as it flows towards the heart Backflow of blood causes the valves to close

23. Blood Vessels CAPILLARIES Link up arteries and veins in the tissues No muscle Wall made up of one cell thick endothelium Small lumen – just large enough for a red blood cell to squeeze through Pressure falls as blood passes along capillary Blood flowing is slowing down No pulse No valves