Structure of the Cardiovascular System (OCR GCSE Physical Education (PE)): Revision Note

Blood vessels: structure

• The heart is an organ that pumps blood around the body using a double circulatory system 

• This means it works as a dual action pump – two pumps work at the same time to pump blood in two different directions 

• Pulmonary circulation:

  • This system carries deoxygenated blood from the heart to the lungs, where it becomes oxygenated and then carries the blood back to the heart

•  Systemic circulation:

  • This system carries oxygenated blood from the heart to the respiring body tissues, where it delivers the oxygen to the cells for respiration, and then carries the deoxygenated blood back to the heart

Blood and blood vessels 

• Once blood leaves the heart, it is transported around the body by three different types of blood vessels 

  • arteries 

  • capillaries 

  • veins 

• Arteries 

  • Arteries carry blood away from the heart at high pressure 

  • They have thick and elastic walls to withstand the high pressure of blood 

  • A narrow lumen helps to maintain high pressure 

  • The largest artery is the aorta which leaves the heart carries oxygenated blood to the organs and working muscles with oxygen 

• Capillaries 

  • These are very small blood vessels with walls that are just one cell thick 

  • As they are so thin this allows oxygen and nutrients to pass (diffuse) through them

    • Oxygen and nutrients diffuse out of capillaries to the cells

    • Carbon dioxide diffuses from the cells into capillaries  

  • They have very narrow lumen 

  • They occur in large quantities around the muscles providing a very large surface area for gas exchange  

• Veins 

  • Veins carry blood towards the heart at low pressure 

  • The walls of veins are less muscular as they do not need to withstand high blood pressure 

  • They have a wide lumen so there is less resistance to blood flow

  • They contain pocket valves to prevent backflow of blood  

  • The vena cava is the largest vein which enters the heart through the right atrium