The heart

• Diastole:

  • the heart relaxes
  • the atria and then the ventricles fill with blood
  • the volume and pressure of the blood in the heart build as the heart fills
  • pressure in the arteries is at a minimum
• Systole:

  • atria contract followed by the ventricles
  • pressure inside the heart increases dramatically
  • blood is forced out of the right side of the heart to the lungs and from the left side to the main body circulation
  • volume and pressure of the blood in the heart are low at the end of systole and blood pressure in the arteries is at a maximum
• Heart sounds:

  =made by blood pressure closing the heart valves

  (described as 'lub-dub')

  The first sound comes as the blood is forced against the atrio-ventricular valves as the ventricles contract. The second sound comes as a back flow of blood closes the semilunar valves in the aorta and pulmonary artery as the ventricles relax.
• Heart rhythm abnormalities on ECGs:

  • Tachycardia=when the heartbeat is very rapid over 100bpm, this is often normal (e.g. when you exercise or have a fever)
  • Bradycardia= when the heart rate slows down to below 60bpm (many people have bradycardia because they are fit- training makes the heart beat more slowly and efficiently)
• Cardiac muscle is myogenic (it automatically contracts and relaxes) and it never fatigues.
• Atrial diastole= atria relax

  Ventricular diastole= ventricles relax
• Atrial systole= atria contract

  Ventricular systole= ventricles contract
• Cardiac cycle:

  • atrial and ventricular diastole
  • atrial systole
  • ventricular systole
• Diastole:

  • atria and ventricular muscles are relaxed
  • blood will enter the atria (via the vena cava and pulmonary vein) as volume of the atria and ventricles has increased
  • the blood flowing in increases the pressure within the atria
• Atrial systole:

  • atria muscular walls contract, increasing the pressure further
  • this causes the atrioventricular valves to open allowing blood to flow into the ventricles
• Ventricular systole:

  • ventricle muscular walls contract, increasing the pressure
  • this causes the atrioventricular valves to close and the semi-lunar valves to open
  • the blood is pushed out of the ventricles (via the pulmonary artery and aorta)
• Tachycardia= when the heart is beating at over 100bpm
• Bradycardia= when the heart is beating at less than 60 bpm
• Fibrillation= when there is an irregular rhythm of the heart
• Ectopic heartbeat= when there are additional heartbeats that are not in rhythm
• Supraventricular tachycardia = less blood leaves the heart as ventricles do not have time to fill before contracting