What are the five main types of blood vessel and their functions?

  1. Arteries - carry oxygenated blood away from the heart
  2. Arterioles - control blood flow from arteries to capillaries
  3. Capillaries - allow the exchange of gases and nutrients between blood and body cells
  4. Venules - collect blood from capillaries and channel it into veins
  5. Veins - carry deoxygenated blood back to the heart

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State the basic structural layers in arteries, arterioles, veins, and venules and the key functions of these layers.

From the outside inwards, the layers are:

  1. Collagen - provides structural support to maintain shape and provides strength to prevent bursting
  2. Muscle layer - smooth muscle allows constriction or dilation of certain blood vessels
  3. Elastic layer - elastic fibres contain elastin to provide flexibility and minimise changes in pressure
  4. Endothelium - thin inner lining
  5. Lumen - the central cavity of the blood vessel through which the blood flows

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Describe how the structure of a capillary is adapted for its function.

  1. Narrow lumen - slows the flow of blood, allowing more time for the exchange of materials between the blood and the body cells
  2. Thin walls - reduce the diffusion distance for rapid exchange of materials
  3. Numerous and highly branched - provides a large surface area to increase the rate of exchange
  4. Permeate tissues, ensuring no cell is far from a capillary - reduces the diffusion distance

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Describe how the structure of an artery is adapted for its function.

  1. Thick collagen wall - resists bursting
  2. Thick elastic layer - stretches and recoils to maintain pressure
  3. Thick smooth muscle layer - contracts/relaxes to constrict/dilate the lumen to control blood flow

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Describe how the structure of a vein is adapted for its function.

  1. Thin walls (including muscle and elastic layers) - as they carry blood under low pressure
  2. Valves - ensure blood does not flow backwards as the pressure is low
  3. Large lumen - to reduce resistance for blood flow

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Compare the structure of an artery and an arteriole.

Arterioles have a relatively thicker muscle layer and relatively larger lumen compared to arteries.


Arteries have a thicker elastic layer to withstand higher pressure.

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What is the difference between vasoconstriction and vasodilation?

Vasoconstriction is the narrowing of blood vessels like arteries and arterioles due to contraction of the smooth muscle in their walls, which reduces blood flow.


Vasodilation is the widening of these blood vessels due to relaxation of the smooth muscle in their walls, which increases blood flow.

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What adaptations allow the movement of deoxygenated blood to the heart, despite its low pressure and movement against gravity?

  1. Veins have valves that prevent backflow of blood
  2. Contraction of skeletal muscles surrounding the veins when the body moves pushes blood towards the heart
  3. Thin walls of veins allow them to be easily compressed, aiding the flow of blood

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