Physiology Week 9 Flashcards
(15 cards)
What does the P wave on an ECG represent?
Atrial depolarization, leading to atrial contraction (systole).
What does the QRS complex on an ECG represent?
Ventricular depolarization, initiating ventricular contraction (systole).
What does the T wave on an ECG represent?
Ventricular repolarization, leading to ventricular relaxation (diastole).
What are the main phases of the cardiac cycle?
Atrial systole, ventricular systole (isovolumetric contraction and ejection), and ventricular diastole (isovolumetric relaxation and ventricular filling).
What happens during atrial systole?
Atria contract, pushing remaining blood into the ventricles.
What occurs during isovolumetric contraction?
Ventricles contract, pressure rises, AV valves close (S1 heart sound), but semilunar valves remain closed.
What happens during ventricular ejection?
When ventricular pressure exceeds aortic/pulmonary pressure, semilunar valves open, and blood is ejected.
What happens during isovolumetric relaxation?
Ventricular pressure drops, semilunar valves close (S2 heart sound), but AV valves remain closed.
What occurs during ventricular filling?
AV valves open as atrial pressure exceeds ventricular pressure, allowing blood to flow into the ventricles.
How long does one complete cardiac cycle take at a heart rate of 75 beats/min?
About 0.8 seconds.
What does the Wiggers diagram represent?
The relationship between electrical (ECG), mechanical (pressure/volume), and heart sounds in one cardiac cycle.
How do electrical and mechanical events relate in the heart?
Electrical events (ECG) precede mechanical events:
P wave → Atrial contraction.
QRS complex → Ventricular contraction.
T wave → Ventricular relaxation.
What is stroke volume (SV)?
The volume of blood ejected by one ventricle per heartbeat.
Formula: SV = End-Diastolic Volume (135 mL) - End-Systolic Volume (65 mL) = ~70 mL/beat.
What is cardiac output (CO)?
The total volume of blood pumped by each ventricle per minute.
Formula: CO = Stroke Volume × Heart Rate.
Example: If HR = 75 bpm, CO = 70 mL × 75 = 5.25 L/min.
What factors influence stroke volume?
Preload (stretch of the heart), contractility (force of contraction), and afterload (resistance from blood pressure).
