the heart

• structure of the heart :

  • atria
  • ventricles
  • vena cava
  • pulmonary arteries and veins
  • aorta
  • tricuspid and bicuspid valves
  • semi-lunar valves
  • coronary arteries
• functions of the heart :

  • double pump

  • diastole

  • systole

  • cardiac cycle
• The heart is sometimes referred to as a double pump. It pumps blood through 2 separate circulatory systems:

  Pulmonary - the right side of the heart receives deoxygenated blood from the body and it pumps it to the lungs

  Systemic - the left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body.
• The flow of blood is called the cardiac cycle. This takes place, on average, about 70 times a minute.

  The part of the cycle when the ventricles are contracting is known as systole ie ventricles are contracting with the atrio-ventricular valves closed and the semilunar valves open.

  Diastole is when both ventricles and atria are relaxed, the atrio-ventricular valves are open, the semilunar valves are closed and the heart fills with blood.
• Stages of the cardiac cycle:

  • Atrial systole - contraction of the right and left atria
  • Ventricular systole - contraction of the ventricles
  • Complete cardiac diastole - relaxation of the atria and ventricles.
• Cardiac cycle


  Regulated by electrical signals
• Sinoatrial node (SA)


  • Located in the upper wall of the right atrium
  • Known as the 'pacemaker'
  • Responsible for setting the rhythm of the heart
  • Ensures both atria contract at the same time
• Atrioventricular node (AV)


  • Situated at the bottom of the right atrium of the heart
  • Responsible for delaying the electrical impulses from the SA node to allow time for blood to flow from the atrium into the ventricles
• • Purkinje / Purkyne fibres fine specialised cardiac muscle fibres that rapidly transmit impulses from the AV node to the ventricles • Bundles of this takes the impulse from the AV node to the bottom of the ventricles
• Heart


  Specialized cardiac muscle that does not tire like other muscles around the body
• Heart


  • Split into four chambers
  • Two upper chambers are the right atrium and left atrium
  • Two lower chambers are the right and left ventricles
  • Left ventricle has the thickest muscular wall to pump blood to the rest of the body
• Aorta


  Main artery of the body, leaves the heart from the left ventricle
• Pulmonary artery


  Carries deoxygenated blood from the heart to the lungs
• Vena cava


  One of the largest veins in the body, carries deoxygenated blood to the right atrium
• Pulmonary vein


  Carries oxygenated blood from the lungs to the left atrium
• Heart valves


  • Tricuspid
  • Bicuspid (mitral)
  • Pulmonary
  • Aortic
• Tricuspid valve


  Allows blood to flow only from the right atrium to the right ventricle
• Bicuspid (mitral) valve


  Allows blood to flow from the left atrium to the left ventricle
• Pulmonary valve


  Stops blood going back from the pulmonary artery into the heart
• Aortic valve


  Found at the exit of the left ventricle where the aorta begins
• The heart is sometimes referred to as a double pump
• Pulmonary circulation


  Right side of the heart receives deoxygenated blood from the body and pumps it to the lungs
• Systemic circulation


  Left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body
• Cardiac cycle


  Heart contracts (systole) and then relaxes (diastole), repeated 60-80 times per minute
• Stages of the cardiac cycle

  • Atrial systole - contraction of the atria
  • Ventricular systole - contraction of the ventricles
  • Complete cardiac diastole - relaxation of the atria and ventricles
• The cardiac cycle is controlled by the electrical activity in the heart
• Sinoatrial (SA) node


  • Located in the upper wall of the right atrium of the heart
  • Known as the 'pacemaker' and is responsible for setting the rhythm of the heart
  • Ensures both atria contract simultaneously
• Atrioventricular (AV) node


  • Located at the bottom of the right atrium of the heart
  • Responsible for delaying the electrical impulses it receives from the SA node
  • Delay allows time for blood to empty out of the atria into the ventricles
• Purkinje fibres


  • Very fine specialised cardiac muscle fibres
  • Rapidly transmit impulses from the atrioventricular node to the ventricles
• Electrocardiogram (ECG) trace


  • Shows the spread of the electrical signal generated by the SA node as it travels through the atria, the AV node and the ventricles
  • Normal ECG trace shows five waves: P, Q, R, S and T
• The P wave at the beginning shows atrial contraction
• The QRS complex shows ventricular contraction (systole)
• The T wave shows ventricles relaxing (diastole)
• If the waves are disordered or out of rhythm, the ECG trace indicates which part of the heartbeat is problematic