Blood Vessels: Structure & Function (Edexcel IGCSE Biology) : Revision Note

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Blood Vessels

  • There are three main types of blood vessel:

    • Arteries

    • Veins

    • Capillaries

  • Smaller vessels that branch off from arteries are called  arterioles (small arteries) and those that branch into veins are called venules (small veins)

  • Each vessel has a particular function and is specifically adapted to carry out that function efficiently

Arteries

  • Key features:

    • Carry blood at high pressure away from the heart

    • Carry oxygenated blood (except the pulmonary artery)

    • Have thick muscular walls containing elastic fibres

    • Have a narrow lumen

    • Blood flows through at a fast speed

  • The structure of an artery is adapted to its function in the following ways

    • Thick muscular walls containing elastic fibres withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through

    • A narrow lumen also helps to maintain high pressure

Veins

  • Key features:

    • Carry blood at low pressure towards the heart

    • Carry deoxygenated blood (other than the pulmonary vein)

    • Have thin walls

    • Have a large lumen

    • Contain valves

    • Blood flows through at a slow speed

  • The structure of a vein is adapted to its function in the following ways:

    • A large lumen reduces resistance to blood flow under low pressure

    • Valves prevent the backflow of blood as it is under low pressure

Comparing arteries and veins, IGCSE & GCSE Biology revision notes

Comparing the structure of arteries and veins

Capillaries

  • Key features:

    • Carry blood at low pressure within tissues

    • Carry both oxygenated and deoxygenated blood

    • Have walls that are one cell thick

    • Have ‘leaky’ walls

    • Speed of blood flow is slow

  • The structure of a capillary is adapted to its function in the following ways:

    • Capillaries have walls that are one cell thick (short diffusion distance) so substances can easily diffuse in and out of them

    • The ‘leaky’ walls allow blood plasma to leak out and form tissue fluid surrounding cells

Structure of a capillary, IGCSE & GCSE Biology revision notes

Structure of a capillary

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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