Mass transport in humans

1. Mass transport in humans By the end of this lesson you should: -be able to describe the structure of arteries, veins, arterioles and capillaries and explain how they are adapted to their function. -understand the importance of the capillaries in metabolic exchange -be able to name the major arteries and veins in the human body.

2. What do you already know?

3. Blood vessels

4. Comparison of blood vessels Use the information to complete the table. Remember to extend you answer and say how the structure assists the function of the vessel.

5. Arteries and arterioles • Carry blood under high pressure. • Elastic fibres allow artery to expand with pulse. • Muscle fibres have ability to contract and push blood along. • Endothelial cells are smooth and allow blood to flow freely. • The middle layer of arterioles has a higher proportion of muscle fibres to elastic tissue. • Muscle cells can contract and partially shut off blood flow to particular organs, for example during exercise blood flow to the stomach is reduced.

6. Veins and Venules • Have much thinner walls than arteries. • The blood is under much lower pressure. • Wider central lumen • Middle layer has fewer elastic fibres and muscle cells. • Contain valves to ensure that the blood can only flow towards the heart. • During exercise blood can be helped to move to the heart by the contraction of arm and leg muscles which puts pressure on veins.

7. Capillaries • Walls consist of a single endothelial cell wrapped into a tubular shape. • Walls are one cell thick-allows for rapid diffusion of substances into vessels. • Oxygen, carbon dioxide, hormones, glucose and amino acids can pass out of capillaries and into tissues.

8. Quick quiz • Which blood vessel contains valves? • Why? • Which blood vessels has a thick layer of smooth muscle and elastic tissue? • Why? • Which layer do arterioles have in a higher proportion to arteries? • How thick are capillaries?

9. Blood vessels that you need to know! Pulmonary artery -Heart  Lungs Pulmonary vein-Lungs  Heart Aorta -Heart  Body Vena Cava -Body  Heart Renal artery- Blood entering kidneys Renal vein- Blood leaving kidneys Hepatic artery- Blood entering liver Hepatic vein- Blood leaving liver Hepatic portal vein-Stomach  LIVER

10. Capillaries Metabolic exchange -substances out of blood into cells -substances out of cells and into blood

11. Leakyvessels Thin walled = substances that cells need can pass out such as O2, CO2, glucose, amino acids and hormones Large molecules e.g. proteins cannot

12. Tissue fluid Vessels are so leaky = produces a solution that fills spaces between cells = tissue fluid

13. Tissue Fluid Hydrostatic pressure large enough to force water out of capillary As blood passes along capillaries water content decreases As water is lost concentration of proteins in blood plasma increases

14. Tissue Fluid Water Potential inside capillary =lower At venule end of capillary water re-enters capillary by osmosis

15. Lymph capillaries Not all water in tissue fluid is reabsorbed into blood by osmosis Lymphatic drainage system = lymph capillaries Lymph capillaries slightly wider than blood capillaries

16. Lymphatic drainage Sufficiently porous for tissue fluid and large molecules to enter Some proteins do escape from blood capillaries and if left to accumulate in the tissue fluid would lower water potential and no water would be reabsorbed into blood

17. True or false? • Hydrostatic pressure forces water out of the blood at the venule end of the capillary. • Water moves back into the blood by osmosis at the venule end of the capillary. • Not all water in the tissue fluid is reabsorbed into the blood by osmosis. • Proteins can enter the lymphatic vessels. • Glucose is found in tissue fluid.

18. At the arteriole end of the capillary, water (hydrostatic) pressure is higher inside the capillary than outside. At the venule end of the capillary there is a higher water potential outside the capillary than inside the capillary. The accumulation of water in the tissue fluid, increases the water potential of the tissue fluid. The water potential becomes equal in the capillaries and the tissue fluid. Therefore, not all water re-enters the capillaries by osmosis. Water moves out of the tissue fluid and into the capillary by osmosis. Remaining water and large molecules drain into the lymphatic system. Large molecules are drained into the lymphatic system as they can lower the water potential of the tissue fluid. The difference in hydrostatic pressure forces the water out of the capillary.

19. Problems with lymphatic drainage. Elephantitis. Worms block the lymphatic vessels. Malnutrition. The child’s blood contains very few plasma proteins.

20. Problems with lymphatic drainage. Elephantitis. Worms block the lymphatic vessels. The lymphatic vessels drain large molecules and excess water from the tissue fluid. Draining large molecules ensures that the water potential of the tissue fluid stays high so that water moves back into the blood. When the lymphatic vessels are blocked water does not move back into the blood and collects in the tissues. Malnutrition. The child’s blood contains very few plasma proteins. The blood has a relatively high water potential. Water will leave the blood at the arteriole end of the capillary due to hydrostatic pressure. However, water will not re-enter at the venule end as the water potential of the blood is high.