2.6

• Cardiac cycle

  The pattern of contraction (systole) and relaxation (diastole) shown by the heart in one complete heartbeat
• Stages of a heartbeat

  • Atrial systole
  • Ventricular systole
  • Diastole
• Diastole

  Blood returning to the atria flows into the ventricles
• Atrial systole

  Transfers the remainder of the blood through the atrio-ventricular (AV) valves to the ventricles
• Ventricular systole

  Closes the AV valves and pumps the blood out through the semi-lunar valves to the aorta and pulmonary artery
• Atrio-ventricular (AV) valves

  Prevent the backflow of blood from the ventricle to atria
• Semi-lunar valves

  Prevent the backflow of blood from the aorta and pulmonary artery back into the ventricles
• The opening and closing of the AV and SL valves are responsible for the heart sounds using a stethoscope
• Cardiac output

  The volume of blood pumped through each ventricle per minute
• Sino-atrial node (SAN)

  Sends electrical impulses through atria causing atrial systole
• Atrio-ventricular node (AVN)

  Sends impulses down between ventricles and up each side to cause ventricular systole
• Electrocardiogram (ECG)

  Detects electrical impulses in the heart
• Parts of ECG trace

  • P - Impulses spreading over atria from SAN causing atrial systole
  • QRS - Impulses through ventricles causing ventricular systole
  • T - Electrical recovery of ventricles at the end of ventricular systole
• Medulla

  Regulates the rate of the sino-atrial node (SAN) through the antagonistic action of the autonomic nervous system (ANS)
• Sympathetic nerves

  Release noradrenaline which increases the heart rate
• Parasympathetic nerves

  Release acetylcholine which slows down heart rate
• Sphygmomanometer

  Instrument used to measure blood pressure
• Blood pressure increases during ventricular systole


  Blood pressure decreases during diastole
• Systolic pressure

  The amount of pressure in your arteries during the contraction of your heart muscle
• Diastolic pressure

  Your blood pressure when your heart muscle is between beats
• A typical blood pressure reading for a young adult is 120/80 mmHg
• Hypertension

  High blood pressure, a major risk factor for many diseases including coronary heart disease and strokes