3. Heart & Blood circulatory system

• Where is the heart located?

  In the thoracic cavity

  Ribs space 3-6
• What landmarks are associated with the heart in the thoracic cavity?

  Mediastinum

  Cardiac notch
• What are the boundaries surrounding the heart?

  Cranially = Thymus

  Caudally = Diaphragm
• Where is the cardiac notch located?

  Between the cranial & middle lobes of the right lung
• What is the point of maximal intensity (PMI) for the mitral valve in dogs?

  Left apex
• Where is the aortic valve located in dogs?

  Left base
• What is the location of the pulmonic valve in dogs?

  Left base
• Where is the tricuspid valve located in dogs?

  Right apex
• What is the PMI location for dogs?

  Left side, 5th intercostal space
• Where is the PMI located in cats?

  Left side, 5th-6th intercostal space
• What is the PMI location for dogs at the 4th intercostal space?

  Left side, just above costochondral junction
• Where is the PMI located for dogs at the 2nd-4th intercostal space?

  Left side, just above sternum
• What is the PMI location for cats at the 2nd-3rd intercostal space?

  One third of the way up from sternum
• Where is the PMI located for dogs on the right side?

  3rd-5th intercostal space near costochondral junction
• What is the PMI location for cats on the right side?

  4th-5th intercostal space near sternum
• What is the primary supply for coronary circulation?

  L and R coronary arteries
• Which coronary artery is larger in dogs?

  Left coronary artery
• When does perfusion occur in coronary circulation?

  During ventricular diastole
• What drains the coronary circulation?

  Great cardiac vein
• Where does the great cardiac vein drain into?

  Right atrium via coronary sinus
• What percentage of cardiac output does coronary circulation account for?

  4-5%
• What are the types of heart valves and their characteristics?

  • Atrioventricular valves:
  • Tricuspid: 3 cusps
  • Mitral (bicuspid): 2 cusps
  • Semilunar valves:
  • Aortic: 3 cusps
  • Pulmonary: 3 cusps
• What is the function of chordae tendineae?

  Prevents eversion of cusps into atrium
• What do papillary muscles do?

  Ensure unidirectional movement of blood
• What is the structure and function of the cardiac skeleton?

  • Annulus fibrosus:
  • Separates atria and ventricles
  • Point of attachment
  • Provides insulation for AV bundle
• What are the three layers of the heart from inside to outside?

  1. Endocardium: Continuous with blood vessel lining
  2. Myocardium: Contains cardiomyocytes
  3. Epicardium: Visceral pericardium
• What are the layers of the pericardium?

  • Inner (visceral) layer: Epicardium/surface of heart
  • Outer (parietal) layer: No significant lumen
• What are cardiomyocytes?

  Large, cylindrical striated cells
• What is the structure of cardiomyocytes?

  Short, branched fibers with intercalated disks
• What happens to cardiomyocytes when damaged?

  They cannot regenerate
• How do cardiac and skeletal muscle differ?

  • Cardiac:
  • Striated, involuntary, branched
  • Functional syncytium, gap junctions
  • Skeletal:
  • Striated, voluntary, unbranched
  • Requires nerve stimulation
• What is the role of gap junctions in cardiac muscle?

  Facilitates electrical communication
• What is hypertrophy in cardiomyocytes?

  Increase in cell size due to training
• What is the sarcoplasmic reticulum's role in cardiac muscle?

  Stores calcium ions for contraction
• What is the structure and function of the sarcomere?

  • Structure:
  • Composed of myofibrils
  • Contains actin and myosin filaments
  • Function:
  • Responsible for muscle contraction
• What is the function of intercalated discs?

  • They allow for the action potential to pass between cells
  • Communication
• What communication occurs via intercalated discs?

  • Ion channels (Na, K, Water, ATP, Ca ions)
  • Receptors (mechanoreceptors, virus receptors, death receptors)
  • Enzymes (kinases, proteases)
• What are Purkinje fibres?

  Specialised cardiac muscle fibres that conduct electrical impulses through the ventricles of the heart.
• What is the delivery system of blood in the body?

  Arteries and arterioles
• What percentage of blood volume is in arteries and arterioles?

  ~15%