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Anatomy & Physiology: Cardiac Physiology and ECG

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  • What is the role of the cardioacceleratory center in heart function?
    The cardioacceleratory center increases both heart rate and force by stimulating the SA and AV nodes and heart muscle.
  • How does the cardioinhibitory center affect the heart?
    The cardioinhibitory center decreases heart rate by inhibiting the SA and AV nodes via the vagus nerves.
  • What is the significance of the long action potential in contractile cardiac muscle cells?
    The long action potential and contraction ensure sustained contraction for efficient ejection of blood from the heart.
  • What does the P wave represent on an ECG?
    The P wave represents depolarization of the SA node and atria.
  • What electrical events are represented by the QRS complex on an ECG?
    The QRS complex represents atrial repolarization and ventricular depolarization.
  • What does the T wave on an ECG indicate?
    The T wave indicates ventricular repolarization.
  • Define the P-R interval on an ECG.
    The P-R interval is the time from the beginning of atrial excitation to the beginning of ventricular excitation.
  • What is the cardiac cycle?
    The cardiac cycle is the blood flow through the heart during one complete heartbeat, involving pressure and volume changes.
  • What is systole and diastole?
    Systole is the period of heart contraction, and diastole is the period of heart relaxation.
  • What causes the 'lub' and 'dup' heart sounds?
    'Lub' is caused by closing of AV valves at ventricular systole start; 'dup' is caused by closing of semilunar valves at ventricular diastole start.
  • How is cardiac output (CO) calculated?
    Cardiac output = Heart rate × Stroke volume (CO = HR × SV).
  • What is stroke volume (SV)?
    Stroke volume is the amount of blood pumped out of each ventricle during a heartbeat, calculated as SV = EDV - ESV.
  • Define end-diastolic volume (EDV) and end-systolic volume (ESV).
    EDV is the blood volume in ventricles at end of diastole; ESV is blood remaining in ventricles after systole.
  • Which hormones regulate heart rate chemically?
    Acetylcholine (via vagus nerve) slows heart rate; epinephrine and thyroxine increase heart rate.
  • Why is ion balance important for heart function?
    Intracellular and extracellular ion concentrations must be maintained for normal heart function; imbalances can be dangerous.
  • What causes the plateau phase in the cardiac muscle action potential?
    The plateau phase is due to Ca2+ influx through slow Ca2+ channels, keeping the cell depolarized while K+ channels are closed.
  • What happens during repolarization of cardiac muscle cells?
    Repolarization occurs when Ca2+ channels close and K+ channels open, allowing K+ to exit and restore membrane potential.
  • What is the absolute refractory period in cardiac muscle?
    The absolute refractory period is the time during which cardiac muscle cannot be re-excited, ensuring proper contraction and relaxation cycles.
  • What is a normal sinus rhythm on an ECG?
    A normal sinus rhythm shows regular P waves followed by QRS complexes, indicating normal SA node function.
  • What characterizes junctional rhythm on an ECG?
    Junctional rhythm occurs when the SA node is nonfunctional; P waves are absent and the AV node paces the heart at 40–60 beats per minute.
  • What is ventricular fibrillation?
    Ventricular fibrillation is chaotic, disorganized electrical activity causing ineffective ventricular contractions and is life-threatening.