CIE IGCSE Biology

Revision Notes

9.4 Blood Vessels

Arteries, Veins & Capillaries

Arteries

  • Carry blood at high pressure away from the heart
  • Carry oxygenated blood (other than the pulmonary artery)
  • Have thick muscular walls containing elastic fibres
  • Have a narrow lumen
  • Speed of flow is fast

Veins

  • 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
  • Speed of flow is slow

 

Comparing arteries and veins, IGCSE & GCSE Biology revision notesComparing arteries and veins

Capillaries

  • 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 flow is slow

 

Structure of a capillary, IGCSE & GCSE Biology revision notesStructure of a capillary

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How Structure of Blood Vessels is Adapted to their Function

Arteries

  • Have thick muscular walls containing elastic fibres to withstand high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through
  • Have a narrow lumen to maintain high pressure

Veins

  • Have a large lumen as blood pressure is low
  • Contain valves to prevent the backflow of blood as it is under low pressure

Capillaries

  • Have walls that are one cell thick so that substances can easily diffuse in and out of them
  • Have ‘leaky’ walls so that blood plasma can leak out and form tissue fluid surrounding cells
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Arterioles & Venules

  • As arteries divide more as they get further away from the heart, they get narrower
  • The narrow vessels that connect arteries to capillaries are called arterioles
  • Veins also get narrower the further away they are from the heart
  • The narrow vessels that connect capillaries to veins are called venules

The blood vessel network, IGCSE & GCSE Biology revision notesThe blood vessel network

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Shunt Vessels

  • Sometimes the cardiovascular system needs to redistribute the blood to specific areas of the body
  • For example:
    • During exercise, more of it goes to the working muscles and less of it goes to other body organs such as the digestive system
    • When we are hot, more blood flows through the surface of the skin and when we are cold less blood flows through the surface of the skin
  • This redirection of blood flow is caused by the use of a vascular shunt vessel
  • The shunt vessels can open or close to control the amount of blood flowing to a specific area

 

A shunt vessel in the skin when we are cold, IGCSE & GCSE Biology revision notesA shunt vessel in the skin when we are cold

 

A shunt vessel in the skin when we are hot, IGCSE & GCSE Biology revision notesA shunt vessel in the skin when we are hot

Circulation Around the Body & Important Blood Vessels

  • Blood is carried away from the heart and towards organs in arteries
  • These narrow to arterioles and then capillaries as they pass through the organ
  • The capillaries widen to venules and finally veins as they move away from the organs
  • Veins carry blood back towards the heart

 

The circulatory system, IGCSE & GCSE Biology revision notesThe circulatory system

 

Important blood vessels:

Important Blood Vessels table, IGCSE & GCSE Biology revision notes

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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