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  1. 1. Blood Vessels
  2. 2. Blood Vessels
  3. 3. Blood Vessels
  4. 4. Human arteries and veins
  5. 5. Human arteries and veins
  6. 8. Arteries
  7. 9. <ul><li>The wall of an artery consists of three layers. </li></ul><ul><li>The innermost layer (tunica intima) is endothelium with a connective tissue membrane. </li></ul><ul><li>The middle layer (tunica media) is smooth muscle & elastic fibres. It’s usually the thickest layer. It changes the vessels diameter to regulate blood flow & pressure. </li></ul><ul><li>The outermost layer (tunica adventitia) is connective tissue with elastic & collagen fibres. </li></ul>Arteries
  8. 10. <ul><li>Arteries carry blood away from the heart. </li></ul><ul><li>Pulmonary arteries transport blood that has a low oxygen content from the right ventricle to the lungs. </li></ul><ul><li>Systemic arteries transport oxygenated blood from the left ventricle to the body tissues. </li></ul><ul><li>Blood is pumped from the ventricles into large elastic arteries that branch repeatedly into smaller and smaller arteries until the branching results in microscopic arteries called arterioles. </li></ul><ul><li>The arterioles play a key role in regulating blood flow into the tissue capillaries. </li></ul><ul><li>About 10 percent of the total blood volume is in the systemic arterial system at any given time. </li></ul>Arteries
  9. 11. Arteries
  10. 12. Capillaries
  11. 13. <ul><li>Transported substances (like CO 2 and O 2 ) enter & leave the blood here. </li></ul><ul><li>No exchange of materials takes place in the arteries and veins because their walls are too thick and impermeable. </li></ul><ul><li>Capillaries are very narrow and their wall is one cell thick. </li></ul><ul><li>They have a huge surface area : volume ratio, helping rapid diffusion of substances between blood and cells. </li></ul><ul><li>Capillaries are arranged in networks called capillary beds feeding a group of cells, and no cell in the body is more than 5 cells away from a capillary. </li></ul>Capillaries
  12. 14. Capillary
  13. 16. Capillary
  14. 17. <ul><li>Veins are the blood vessels that carry deoxygenated blood back to the heart. </li></ul><ul><li>The walls of the veins are thinner than the arteries, they have the same three layers in them. There is less muscle and elastic tissue in the middle layer. </li></ul><ul><li>Some veins have valves in them to ensure the flow of blood travels to the heart, and not backwards. </li></ul><ul><li>The smallest of the veins (furthest away from the heart) are known as venules. </li></ul><ul><li>Veins contain about 75% of blood at any time. </li></ul>Veins
  15. 18. Veins
  16. 19. <ul><li>The elastic recoil of arteries </li></ul><ul><li>Gravity (head and shoulders) </li></ul><ul><li>Negative pressure in the thorax having a suction effect on blood in the inferior vena cava </li></ul><ul><li>The contraction of skeletal muscles helping to force blood through veins by squashing them (most important in the legs) </li></ul>Other factors aiding the circulation of blood
  17. 22. Flow dynamics