Blood Vessels (AQA A Level Biology): Revision Note
Exam code: 7402
Arteries, arterioles & veins
The body contains different types of blood vessel, including:
arteries
arterioles
veins
The structure of each type of blood vessel is closely related to function
Blood vessel structure and function
Arteries
Transport blood away from the heart at high pressure
Structure | Function |
|---|---|
Thick walls containing smooth muscle and elastic fibres | Can withstand high pressures generated by the contracting heart Elastic fibres allow stretch to expand around blood when heart beats Elastic enables recoil to maintain blood pressure when the heart is relaxed |
Narrow lumen | Helps to maintain high blood pressure |
Folded inner lining (endothelium) | Can stretch to allow increased blood flow |
Arterioles
Arteries branch into narrower blood vessels called arterioles which transport blood into capillaries
Structure | Function |
|---|---|
Walls contain a lower proportion of elastic fibres and a large number of muscle cells | Pressure is lower than in arteries, so elasticity is less essential Muscle can contract to adjust blood flow to specific organs, e.g. during exercise blood flow to the intestine is reduced while flow to the muscles increases |
Veins
Veins transport blood back to the heart at low pressure
Structure | Function |
|---|---|
Walls are thin with fewer smooth muscle and elastic fibres | The blood in veins is not at high pressure, so thick walls with elastic recoil are not needed |
Lumen is much larger than that of an artery | The large lumen allows a high volume of blood to flow through veins |
Valves are present | Valves prevent backflow of blood |
Examiner Tips and Tricks
Exam questions may ask you to explain the features of blood vessels; in this situation you should always make clear links between structural features and how they aid function.
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