Mammals have a transport mechanism called circulatory system. The circulatory system is composed of the heart and the associated blood vessels



  • Carry blood away from the heart.
  • Blood that flows through arteries is pulsing and at a high pressure.
  • Contain elastic fibres and collagen fibres
  • Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood
  • Have thick, elastic walls which can expand and recoil as the blood pulses through.
  • The artery wall contains variable amounts of smooth muscle.
  • It carries oxygenated blood except in pulmonary artery


Relate the structure of the artery to its function

  • Arteries transport swiftly and at high pressure to the tissues
  • made up of an inner endothelium
    • this layer is very smooth, minimizing friction with the moving blood.
  • also made up of tunica media
    • Contain smooth muscle and elastic fibres
  • Tunica extern
    • Contain elastic fibres and collagen fibres.
    • Arteries have narrow lumen maintaining high pressure facilitate faster movement of blood.
    • Elastic walls to allow for expansion when pressure increases
  • semilunar valves to prevent backflow of blood



  • Carry low-pressure blood back to the heart
  • the lumen is larger than in arteries, reducing friction which would otherwise slow down blood movement
  • Have thin muscular wall with little elastic tissue
  • Contain valves, to prevent the backflow of blood
  • No pulses and blood flows slowly.
  • Deoxygenated blood except pulmonary vein



  • Tiny vessels with just enough space for red blood cells to squeeze through
  • Have no muscles or elastic tissue.
  • Blood flows slowly and no pulses.
  • Large lumen relative to diameter
  • single cell walled and they are permeable and unable to constrict.
  • there are often gaps in the walls through which plasma (the liquid component of blood) can leak out
  • deliver nutrients, hormones and other requirements to body cells, and take away their waste products
  • Small size and thin walls minimize diffusion distance
  • this enables the exchange to take place rapidly between the blood and the body cells.

How the structure of arteries and capillaries is related to their function.

  • artery
    • thick elastic layer in artery
    • even outflow/associated with recoil
    • thick muscular layer to allow pausatile flow of blood;
    • endothelium layer for smooth flow of blood;
    • thick collagen layer to allow blood flow under pressure
    • small lumen allow rapid flow of blood
  • capillary
    • capillary wall is thin/only endothelium
    • gaps for the exchange of materials like white blood cells
    • capillary form a branched network to increase surface area for exchange of materials
    • narrow diameter to minimize diffusion distance
    • narrow lumen -more diffusion efficient

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