The Circulatory System

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  • Created by: abi-hunt
  • Created on: 06-05-18 19:58

arteries

  • arteries carry blood from the heart to the rest of the body
  • their walls are thick and muscular and have elastic tissue to stretch and recoil as the heart beats, which helps maintain a high pressure
  • the inner lining (endothelium) is folded, allowing the artery to stretch - this also helps maintain the high pressure
  • all arteries carry oxygenated blood except for the pulmonary artery which carries deoxygenated blood from the heart to the lungs
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arterioles

  • arteries divide into smaller sections called arterioles
  • these form a network throughout the body
  • blood is directed to different areas of demand in the body by muscles inside the arterioles
  • they contract to restrict the blood flow or relax to allow full blood flow
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veins

  • veins take blood back to the heart under low pressure
  • they have a wider lumen with very little elastic tissue
  • veins contain valves to stop blood flowing backward
  • blood flow through veins is helped by contraction of the muscles surrounding them
  • all veins carry deoxygenated blood, except for the pulmonary vein which carries oxygenated blood from the lungs to the heart
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capillaries

  • arterioles branch into capillaries
  • substances are exchanged between cells and capillaries, so they're adapted for efficient diffusion
  • capillaries are always found very near cells in exchange tissue so there's a short diffusion pathway
  • their walls are only one cell thick
  • there are a large number of capillaries found together to increase the surface area - the networks of capillaries are called capillary beds
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tissue fluid

  • tissue fluid is the fluid that surrounds cells in tissues
  • its made from small molecules that leave the blood plama, eg. oxygen, water and nutrients
  • substances move out of the capillaries, into tissue fluid through pressure filtration
  • at the end of the capillary bed, nearest the arteries, the hydrostatic pressure is greater inside the capillaries than in the tissue fluid
  • as molecules leave through the gaps in capillaires, the pressure in the capillaries is reduced
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