Introduction to cardiovascular system

• Role of the cardiovascular system

  • To provide a continual supply of blood and therefore oxygen and nutrients to the body
  • To remove carbon dioxide and waste products from the tissues
• The heart


  • A closed system comprising cardiac chambers and blood vessels
  • Arteries take blood away from the heart
  • Veins take blood towards the heart
• Anatomy of the heart

  • A conical shaped organ comprised of 2 muscular pumps, each chambers have an atrium and a ventricle
  • Located in the lower thorax in the space between the 2 lungs called the mediastinum
  • Approximately 2/3 lies to the left, 1/3 lies to the right
  • Rests on the diaphragm
• Atria


  Receive blood
• Ventricles


  Pump blood
• The left ventricle is much thicker than the right ventricle as the left ventricle has to pump blood to the whole of the body at a much higher pressure
• Right ventricle


  Pumps blood to lungs (pulmonary circulation)
• Left ventricle


  Pumps blood through the aorta to body (systemic circulation)
• Valves


  • Tricuspid - separates right atrium and ventricle
  • Mitral - separates left atrium and ventricle
  • Pulmonary - between right ventricle and pulmonary artery
  • Aortic - between left ventricle and aorta
• Tricuspid and mitral valves

  Atrioventricular valves
• Pulmonary and aortic valves

  Semilunar valves
• Sequence of events in the cardiac cycle

  1. Backflow of blood in the aorta and pulmonary artery closes the semilunar valves

  2. AV valves and semilunar valves are closed

  3. The weight of blood in the atria causes the AV valves to open

  4. The contraction of the ventricles open the semilunar valves

  5. AV valves close and the semilunar valves open
• Great vessels


  • Superior Vena Cava and Inferior Vena Cava bring blood to the right atrium
  • Pulmonary Trunk dividing into the Right and Left Pulmonary Artery leaves the right ventricle and takes blood to the lungs
  • Pulmonary Veins bring blood to the left atrium
  • Aorta leaves the left ventricle and takes blood to the body
• Layers of the heart

  • Pericardium - tough, fibrous protective sac
  • Myocardium - thick muscular
  • Endocardium - innermost layer
• Pericardium


  • Comprises the fibrous pericardium and serous pericardium
  • The parietal pericardium is continuous with the visceral pericardium which lines the outer surface of the heart muscle
  • The visceral pericardium is known as the epicardium
  • The epicardium contains blood vessels which supply the pericardium
• Myocardium


  • Cardiac muscles fibres are striated, involuntary, branches, and arranged in such a way to form a figure of 8
  • Branching allows fibres to make networks, rapid spread of action potentials, and coordinated contraction of atria and ventricles
• Endocardium


  • Smooth, thin layer of connective tissue, prevents friction and decreases the risk of clotting
  • Lines the inner surface of the chambers
  • Comprised of a single layer of squamous epithelium and a basement membrane
  • Forms part of the endothelium which lines the whole of the circulatory system
• Coronary circulation


  • The heart has its own blood supply, two main coronary arteries
  • Left coronary artery branches into the left anterior descending artery and circumflex artery
  • Right coronary artery
  • The heart has its own blood supply which arises from the aorta the coronary arteries fill with blood on ventricular relaxation
• Left coronary artery/left anterior descending artery

  Supplies both ventricles
• Circumflex artery


  Supplies left ventricles and left atrium
• Right coronary artery


  Supplies right ventricles and right atrium
• The cardiac cycle


  1. Blood returns to the heart

  2. Passive filling of the atria

  3. Tricuspid and Mitral (bicuspid) valves open

  4. Passive blood flow, from atria to ventricles begins

  5. Atria contract

  6. Ventricular filling causes AV valves to close

  7. Ventricles contract

  8. Blood ejected into the systemic circulation via the aorta and the pulmonary circulation via the pulmonary trunk and pulmonary artery
• Conduction system


  1. An excitation signal (an action potential) is created by the sinoatrial (SA) node

  2. The wave of excitation spreads across the atria, causing them to contract

  3. Upon reaching the atrioventricular (AV) node, the signal is delayed

  4. It is then conducted into the bundle of His, down the interventricular septum

  5. The bundle of His and the Purkinje fibres spread the wave impulses along the ventricles, causing them to contract
• P wave


  SA node to AV Node - Atria contract
• QRS complex


  Bundle of His down bundle branches to Purkinje fibres - Ventricles contract
• T wave


  Ventricles relax (repolarisation)
• The right atrium receives deoxygenated blood from the body through the superior vena cava (SVC) and inferior vena cava (IVC).