Circulatory system

• Main functions of the circulatory system

  • Transport - blood cells, food (glucose/amino acids), carbon dioxide, urea
  • Protection against disease
• Red blood cells


  Transport oxygen and are adapted for this by: containing haemoglobin (rich in iron) that oxygen binds to, biconcave shape - gives a large surface area, absence of a nucleus - can carry more haemoglobin
• White blood cells


  Defence against disease: Lymphocytes produce antibodies, Phagocytes engulf and digest microorganisms (= phagocytosis)
• Plasma


  Liquid part of blood; main function is transport of blood cells, food molecules, carbon dioxide, hormones and urea
• Platelets


  Help convert fibrinogen to fibrin in blood clotting - the fibrin forms a mesh to trap the blood - and in the formation of scabs
• Salts and other chemicals in the plasma keep its concentration stable and at a concentration similar to that of the blood cells. This is important, because if red blood cells are placed in water they will take in water by osmosis and burst in a process called cell lysis.
• Types of blood vessels

  • Arteries
  • Veins
  • Capillaries
• Arteries


  • Thick contains muscle for strength, as blood pressure is high, and elastic fibres that allow arteries to expand and recoil as blood pulses through
  • Blood pressure is high
  • No valves
  • Relatively small diameter
• Veins


  • Thinner than artery - less muscle and fewer elastic fibres
  • Blood pressure is low
  • Have valves to prevent backflow of blood
  • Relatively large diameter
• Capillaries


  • One cell thick to allow exchange between the blood and body cells
  • Blood pressure is low
  • No valves
  • Very small diameter
• The heart is the organ that pumps blood round the body.
• Parts of the heart

  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle
• Ventricles


  • Thicker than the atria as they are the chambers that pump the blood
  • Left ventricle has a thicker muscular wall than the right ventricle as it pumps blood round the body - not just to the lungs
• The valves prevent backflow and make sure that the heart acts as a unidirectional (one-way) pump.
• The coronary blood vessels supply the heart muscle with blood.
• Regular exercise


  • Strengthens the heart muscle
  • Increases the cardiac output (pump more blood per minute) even when not exercising
• Cardiac output


  The volume (amount) of blood pumped by the heart per minute