Cardiac cycle

• What is the mean arterial pressure in the circulatory system?

  100 mmHg
• What is the normal blood pressure reading for a healthy adult?

  120/80 mmHg
• What does the cardiac cycle consist of?

  A period of contraction (systole) and a period of relaxation (diastole)

  
• What is the average heart rate at rest?

  Approximately 70 bpm
• If the heart rate increases to 200 bpm, what is the approximate duration of the cardiac cycle?

  About 300 ms
• How long is the systole phase during a cardiac cycle at rest?

  Approximately 330 ms
• What is the volume of blood in the ventricles at the end of diastole?

  Approximately 120 ml
• What type of muscle is the heart composed of?

  Cardiac muscle
• What is a key feature of cardiomyocytes?

  They are myogenically active and involuntary
• What do intercalated discs in cardiac muscle allow for?

  They allow current to flow between adjacent cells

  
• What is the resting potential of the SA node?

  Approximately -55 mV
• What happens when the membrane potential of the SA node reaches -40 mV?

  1. type Ca2+ channels open, leading to depolarization
• What is the role of the autonomic nervous system in heart rate regulation?

  It maintains normal homeostasis, including heart rate
• What effect does sympathetic stimulation have on the SA node?

  It increases Na+ entry and speeds up depolarization
• Where does depolarization start in the heart?

  In the right atrium at the SA node
• What is the function of the AV node during depolarization?

  It slows down the depolarization to allow for complete ventricular filling
• What is the plateau phase in ventricular action potential caused by?

  Increased influx of Ca2+ at the same time as K+ efflux
• What prevents the heart from tetanic contraction?

  The plateau and refractory period of the cardiac action potential
• What are the four valves in the heart?

  Mitral, tricuspid, aortic, and pulmonary valves
• What happens to ventricular pressure during diastole?

  It drops to 0 mmHg as the chamber enlarges
• What occurs during isovolumetric contraction?

  No ejection occurs until the semi-lunar valves open
• What is the ejection fraction during systole?

  Approximately 60% of end-diastolic volume
• What does the P wave in an ECG represent?

  Depolarization of the atria

  
• What does the QRS complex in an ECG indicate?

  Depolarization of the ventricles
• What does the T wave in an ECG represent?

  Ventricular repolarization

  
• What does the PR interval in an ECG measure?

  Conduction through the AV node
• What does the QT interval represent?

  The time taken for ventricular depolarization and repolarization
• What causes the first heart sound during the cardiac cycle?

  Closing of the AV valves as the ventricles contract
• What is the significance of the third heart sound?

  It indicates the transition between rapid and slow filling of the ventricle
• What does a phonocardiogram detect?

  Heart sounds including the third and fourth heart sounds
• What are the main components of the cardiac cycle?

  • Systole: contraction phase
  • Diastole: relaxation phase
  • Heart rate influences duration
  • Volume and pressure changes throughout

  
• What are the key features of cardiac muscle?

  • Myogenically active (involuntary)
  • Irregular Y-shaped fibers
  • Mostly single nucleated (can be binucleated)
  • Striated appearance
  • Connected by intercalated discs
• What is the conduction pathway of the heart?

  1. Depolarization starts at the SA node
  2. Spreads through the atria
  3. Reaches the AV node (slowed)
  4. Rapid spread down Bundle of His and Purkinje fibers
  5. Spreads through ventricular muscle

  
• What are the phases of the ventricular action potential?

  1. Phase 0: Fast Na+ influx
  2. Phase 1: Initial repolarization (K+)
  3. Phase 2: Plateau (K+ and Ca2+)
  4. Phase 3: Repolarization (K+)
  5. Phase 4: Resting potential
• What are the types of heart sounds and their significance?

  • 1st heart sound: Closing of AV valves ("Lubb")
  • 2nd heart sound: Closing of aortic and pulmonary valves ("Dub")
  • 3rd heart sound: Transition between rapid and slow filling
  • 4th heart sound: Atrial systole (pathological)
• What are the ways to measure the cardiac cycle?

  • Electrocardiogram (ECG)
  • Phonocardiogram (heart sounds)

  
• What are the intervals and segments in an ECG and their significance?

  • PR Interval: Conduction through AV node
  • QT Interval: Time for ventricular depolarization and repolarization
  • ST Segment: Interval between depolarization and repolarization