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KS4 GCSE revision - The Circulatory System

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All the cells in the body need OXYGEN and FOOD to stay alive and it is the CIRCULATORY SYSTEM which transports them, along with many other things, around the body.
 
  • The functions of the Circulatory System:
    • To carry OXYGEN to all the cells in the body
    • To carry FOOD to all the cells in the body
    • To remove WASTE from the cells of the body
    • To distribute HEAT around the body
    • To form a part of the DEFENCE the body has against microbes
    • To REPAIR itself and prevent blood loss by clotting
 
  • The parts of the Circulatory System:
    • The HEART
    • The ARTERIES
    • The VEINS
    • The CAPILLARIES
    • The RED and WHITE BLOOD CELLS
    • The PLATELETS
    • The PLASMA
Diagram of the Heart The 'DOUBLE' pump of the Human Heart
  1. Deoxygenated blood FROM THE BODY entering the heart
  2. The RIGHT ATRIUM
  3. The VALVES prevent blood flowing the wrong way when the atria and ventricles contract
  4. The RIGHT VENTRICLE
  5. The thicker walled LEFT VENTRICLE
  6. The LEFT ATRIUM
  7. Oxygenated blood FROM THE LUNGS entering the heart
  8. Oxygenated blood leaving the heart and flowing TO THE BODY
  9. Deoxygenated blood leaving the heart and flowing TO THE LUNGS

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The structure of the heart.
  • The heart is made of MUSCLE and has FOUR chambers, two on each side. The ATRIA are the two upper chambers and are smaller and less muscular. The lower chambers are the VENTRICLES and these are larger and more muscular. The LEFT VENTRICLE is more muscular than the right since it has to pump oxygenated blood around the whole BODY. The RIGHT VENTRICLE only has to pump deoxygenated blood around the LUNGS.
How blood moves through the heart.

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  • A Vein takes blood to the heart where it enters an Atrium.
  • This contracts and forces the blood into a Ventricle.
  • This then contracts and forces the blood out of the heart and into an Artery
Remember: Vein -> Atrium -> Ventricle -> Artery    i.e. A V A V

Valves in the heart prevent the blood flowing back the wrong way when the VENTRICLES and ATRIA contract.

How blood moves outside the heart.

The major arteries divide and divide until they become microscopic CAPILLARIES (these are so thin-walled that molecules are easily exchanges between the blood and the surrounding tissues). The capillaries join together to form veins which join other veins to form the major veins which take the blood back to the heart.
(Remember: Blood passes through the heart twice during a complete circulation)

 
The different Blood Vessels

Cross section of an ARTERY

  • Arteries always carry blood away from the heart. (Remember: AAA)
    All arteries carry OXYGENATED blood except the one carrying blood from the heart TO THE LUNGS.
    Arteries have:
    • THICKER WALLS
    • SMALLER LUMEN
    • MORE ELASTIC and MORE MUSCLE FIBRES
    • NO VALVES

    Cross section of a VEIN

  • Veins always carry blood towards the heart. All veins carry DEOXYGENATED blood except the one carrying blood FROM THE LUNGS to the heart.
    Veins have:
    • THINNER WALLS
    • LARGER LUMEN
    • LESS ELASTIC and LESS MUSCLE FIBRES
    • VALVES to help blood return to the heart

  • Capillaries are microscopic and their walls are only ONE CELL THICK. They have NO VALVES and they LINK ARTERIES to VEINS.
    Cross section of a CAPILLARYFOOD and OXYGEN pass out through the thin walls into the cells and WASTE and CARBON DIOXIDE enter the blood and are carried away. View a movie file of red-blood cells moving through a capillary.

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    View a simplified animation of the blood flow through the heart. (Macromedia Shockwave required)

 


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