Week 10 - Cardiac Physiology

• How is the heart controlled?

  By hormonal and neural influences
• What is the output of the right ventricle?

  It enters the pulmonary artery
• What is the output of the left ventricle?

  It enters the aorta
• What regulates the output of the heart?

  It is under intrinsic control and can be extrinsically regulated
• What is the blood pressure in the pulmonary circuit?

  Approximately 28/8 mmHg
• What is the blood pressure in the systemic circuit?

  Approximately 120/80 mmHg
• What are the steps in the sequence of events in the cardiac cycle?

  1. Venous return to the right atrium
  2. Mixed venous blood fills the right ventricle
  3. Blood is ejected from the right ventricle into the pulmonary artery
  4. Blood flow from the lungs is returned to the heart via the pulmonary vein
  5. Oxygenated blood fills the left ventricle
  6. Blood is ejected from the left ventricle into the aorta
  7. Cardiac output is distributed among various organs
  8. Blood flow from the organs is collected in the veins
• What is heart failure defined as?

  The heart is unable to pump blood at a rate required by metabolizing tissues
• What does the cardiac cycle include?

  A complete relaxation and contraction of both atria and ventricles
• What are the two phases of the cardiac cycle?

  Diastole and systole
• What causes pressure changes in the heart during the cardiac cycle?

  A series of pressure changes occur due to movement of blood through different chambers
• What role do valves play in the heart?

  They direct the movement of blood
• What initiates pressure changes in the heart?

  Conductive electrochemical changes within the myocardium
• What are the phases of the cardiac cycle (left side)?

  1. Atrial contraction (mitral valve closes)
  2. Ventricular isovolumetric contraction (aortic valve opens)
  3. Rapid ventricular ejection
  4. Slow ventricular ejection (aortic valve closes)
  5. Ventricular isovolumetric relaxation (mitral valve opens)
  6. Ventricular filling
  7. Diastasis
• What is the function of intercalated discs in cardiac muscle?

  They link muscle cells together and contain desmosomes and gap junctions
• How do gap junctions function in cardiac muscle?

  They allow passage of action potentials from one cell to the next
• What is the significance of desmosomes in cardiac muscle?


  They hold the muscle cells together tightly
• What is automaticity in myocardial cells?

  Myocardial cells can spontaneously depolarize
• What is the role of calcium in cardiac muscle contraction?

  Calcium is the crucial mediator that couples electrical excitation to physical contraction
• What happens during calcium-induced calcium release?

  Initial influx of Ca$^{2+}$ triggers greater release from the sarcoplasmic reticulum
• Who developed the galvanometer to show action potentials in 1901?

  William Einthoven
• What does Einthoven's Triangle represent?

  It helps identify which lead will best show certain electrical activity
• What does the ECG trace represent?

  It is an electrical trace resulting from action potentials in heart muscle fibers
• What does the P wave represent in an ECG?

  Depolarization of the atrial muscle cells
• What does the QRS complex represent in an ECG?

  Depolarization of ventricular muscle
• What does the PR interval indicate?

  It measures the time from atrial depolarization to ventricular depolarization
• What is the end diastolic volume (EDV) at rest?

  Approximately 130 ml
• What is the end systolic volume (ESV) at rest?

  Approximately 60 ml
• How is stroke volume (SV) calculated?

  SV = EDV - ESV
• What is the formula for cardiac output?

  Cardiac Output = Stroke Volume x Heart Rate
• What happens to venous return during physical activity?

  It increases due to the skeletal muscle pump
• How does afterload affect stroke volume?

  The higher the arterial pressure, the lower the stroke volume
• What is the significance of fibrous tissue surrounding the atrioventricular valve openings?

  It electrically isolates atria from ventricles
• What is the role of ion channels in cardiac action potentials?

  They control the movement of ions across the membrane
• What happens during repolarization of cardiac muscle cells?

  K$^{+}$ leaves the cell, returning the membrane potential to resting levels
• What is the pacemaker potential?

  It is the gradual decrease of resting membrane potential in SAN cells
• What triggers an action potential in pacemaker cells?

  When the membrane potential exceeds a threshold
• How often does the SAN generate action potentials at rest?

  Approximately every 0.8 seconds
• How can the SAN's action potential generation be influenced?

  By sympathetic and parasympathetic nerves
• What is excitation-contraction coupling?

  It is the process by which an electrical action potential leads to contraction of cardiac muscle cells