The Circulatory System

  • The circulatory system consists of the heart and the blood vessels (veins, arteries and capillaries).
  • Veins bring blood away from the heart. They have a wider lumen and thinner walls than arteries, and valves to prevent backflow of blood.
  • Arteries carry blood away from the heart. they have a narrow lumen, thick walls and no valves.
  • Capillaries are thin blood vessels(1 cell thick) that allow substances to pass into and out of the blood. They join veins to arteries.


  • Plasma is the liquid part of the blood .
  • Red blood cells are the most numerous blood cells. They are made in bone marrow and they contain haemoglobin to transport oxygen. They also give the blood its red colour.
  • Iron is needed to make red blod cells.
  • White blood cells fight disease.
  • Platelets clot the blood to stop bleeding.
  • Red blood cells have a biconcave shape and no nucleus.

The Heart

  • The heart is made of cardiac muscle – a type of muscle which never tires.
  • It contracts to pump blood around the body.
  • It consists of 4 chambers – right & left atriums, right & left ventricles.
  • The right side of the heart pumps deoxygenated blood to the lungs.
  • The left side of the heart pumps oxygenated blood to the rest of the body. The heart wall is therefore thicker/stronger on the left.
  • The heart has 2 valves to control the direction of the flow of blood.

Exercise and the rate of heartbeat

  • The normal heartbeat rate of a resting human is 70 beats per minute.
  • Exercise increases the heartbeat rate. This is because during exercise the cells need to produce more energy, so they require more food and oxygen.
  • The normal body temperature in the human body is 37°C.