Blood Vessels And Their Function

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ARTERY STRUCTURE RELATED TO FUNCTION:

  • Transports blood rapidly under high pressure from the heart to the tissues.
  • Their structure is adapted to this function as follows:
    • The muscle layer is thick compared to veins - this means smaller arteries can be constricted and dilated in order to control the volume of blood passing through them.
    • The elastic layer is relatively thick compared to veins - because it is important that blood pressure in arteries is kept high if blood is to reach the extremities of the body. The elastic wall is stretched at each beat of the heart (systole). It then springs back when the heart relaxes (diastole) in the same way as a stretched elastic band. This stretching and recoiling action helps to maintain high pressure and smooth pressure surges created by the beating of the heart.
    • The overall thickness of the wall is great - this also resists the vessel bursting under pressure.
    • There are no valves - (except in the arteries leaving the heart) because blood is under constant high pressure due to the heart pumping blood into the arteries. It therefore tends not to flow backwards.

ARTERIOLE STRUCTURE RELATED TO FUNCTION:

  • Carry blood, under lower pressure than arteries, from arteries to capillaries.
  • They also control the flow of blood between the 2.
  • Their structure is related to these functions as follows:
    • The muscle layer is relatively thicker than in arteries - the contraction of this muscle layer allows constriction of the lumen of the arteriole. This restricts the flow of blood and so controls its movements into the capillaries that supply the tissues with blood.
    • The elastic layer is relatively thinner than in arteries - becasue blood pressure is lower.

VEIN STRUCTURE RELATED TO FUNCTION:

  • Transport blood slowly, under low pressure, from the capillaries in tissues to the heart.
  • Their structure is related to this function as follows:
    • The muscle layer is relatively thin - compared to arteries becasue veins carry blood away from tissues and therefore their constriction and dilation cannot control the flow of blood to the tissues.
    • The elastic layer is relatively thin - compared to arteries becasue the low pressure of blood within the veins will not cause them to burst and pressure is too low to create a recoil action.
    • The overall thickness of the wall is small - because…

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