The structure of the heart

• Atria - The upper chambers of the heart which are thin-walled and elastic and stretches as it collects blood
• Ventricles - The lower chambers of the heart which have a much thicker muscular wall as it has to contract strongly to pump blood some distance, either to the lungs or to the rest of the body
• Ventricles pump blood either:

  • Left side to the rest of the body (thus a thicker muscular wall)
  • Right side to the lungs
• Right ventricle - Pumps blood only to the lungs, (so has a thinner muscular wall than the left ventricle as it's a shorter distance)
• Left ventricle - Pumps blood to the rest of the body

  • Thick muscular wall, enabling it to contract to create enough pressure to pump blood to the rest of the body
• The left ventricle has a thicker, more muscular wall than the right ventricles as it allows it to contract with more force and push blood at a higher pressure out through the aorta so it can travel to the whole body
• Between each atrium and ventricle are valves that prevent the backflow of blood into the atria when ventricles contract. There are two valves:

  • Left atrioventricular (bicuspid) valve
  • Right atrioventricular (tricuspid) valve
• Atrioventricular valves - The valves found between the atrium and ventricle which prevent the backflow of blood into the atria when the ventricles contract and the ventricular pressure exceeds atrial pressure

  • Left is bicuspid, right is tricuspid
• Aorta:

  • Connected to the left ventricle
  • Carries oxygenated blood to the rest of the body
• Vena cava:

  • Connected to the right atrium
  • Brings deoxygenated blood back from the tissues of the body
• Pulmonary artery:

  • Connected to the right ventricle
  • Carries deoxygenated blood to the lungs, where its oxygen is replenished and its carbon dioxide is removed
• Pulmonary vein:

  • Connected to the left atrium
  • Brings oxygenated blood back from the lungs
• • The pulmonary vein is the ONLY vein to carry oxygenated blood
  • The pulmonary artery is the ONLY artery to carry deoxygenated blood
• Supplying the heart muscle with oxygen:

  • The heart muscle receives oxygenated blood through the coronary arteries which branch off the aorta
• Supplying the heart muscle with oxygen:

  • Blockage of these coronary arteries leads to myocardial infarction, or a heart attack, because an area of the heart muscle is deprived of blood and therefore oxygen also
  • The muscle cells in this region are unable to respire and so die
• Semilunar valves - The valves found in the aorta and pulmonary artery which prevent the backflow of blood into the ventricles when the pressure in these vessels exceeds that in the ventricles (e.g just after the ventricles contract)
• Atrioventricular valves - Valves found between the atrium and ventricle

  • Only open one way so prevent the backflow of blood into the atria when the ventricles contract
  • Allow pressure to build in the ventricles as they shut when ventricular pressure exceeds atrial pressure