Module 1 Lesson 3 Flashcards
What ensures atrial excitation and contraction are completed before ventricular events?
Electrical conduction system of the heart
What is the primary function of the sinoatrial (SA) node?
Acts as the heart’s pacemaker, initiating electrical impulses
What does an electrocardiogram (ECG) measure?
The electrical activity induced in body fluids by the cardiac impulse that reaches the body surface.
What are the two phases of the cardiac cycle?
Systole (contraction) and diastole (relaxation)
How long is the cardiac cycle at a heart rate of 75 beats per minute?
0.8 seconds
What happens to ventricular diastole when heart rate increases from 75 to 180 beats per minute?
Ventricular diastole duration is reduced by about 75%.
What are the two main factors that regulate cardiac output?
Heart rate and stroke volume
How does parasympathetic stimulation affect heart rate?
It decreases heart rate by slowing SA node activity and increasing AV node delay.
How does sympathetic stimulation affect heart rate?
It increases heart rate by accelerating SA node activity and conduction velocity at the AV node.
What neurotransmitter is involved in sympathetic stimulation of the heart?
Noradrenaline (Norepinephrine)
Why is it important that atrial contraction occurs before ventricular contraction?
It ensures the ventricles are properly filled with blood before pumping.
How does the cardiac conduction system allow for coordinated heartbeats?
The SA node generates impulses that spread rapidly through the atria, delay at the AV node, and then conduct quickly through the ventricles.
What is the significance of the AV node delay?
It ensures the ventricles contract after the atria have emptied their blood into them.
Why does heart rate increase when the heart is removed from the body?
The parasympathetic nervous system normally slows the heart rate; without it, the intrinsic SA node rate is higher.
Why does parasympathetic stimulation hyperpolarize the SA node?
It increases K⁺ permeability, making it harder for the membrane potential to reach the threshold for an action potential.
Why does sympathetic stimulation increase the rate of depolarization?
It decreases K⁺ permeability and increases inward Ca²⁺ currents, allowing faster reaching of the threshold potential.
How does the cardiac cycle ensure one-way blood flow?
Pressure changes open and close heart valves at the right time.
Why does stroke volume decrease at very high heart rates?
Less time for ventricular filling leads to lower end-diastolic volume.
If a patient’s ECG shows no P waves, what might be happening?
The SA node is not firing, possibly due to sinoatrial block or atrial fibrillation.
How would an AV node block affect the ECG?
It would cause prolonged PR intervals or dissociation between P waves and QRS complexes.
If a patient has a resting heart rate of 50 beats per minute, what could be the cause?
Increased parasympathetic (vagal) activity, which slows the SA node.
How does the body compensate for a decrease in stroke volume?
By increasing heart rate to maintain cardiac output.
If a patient has excessive sympathetic stimulation, what ECG changes might be observed?
Increased heart rate (tachycardia) and possibly shorter PR and QT intervals
How would a beta-blocker affect heart rate?
It would reduce sympathetic activity, leading to a slower heart rate.
Why does the dicrotic notch appear in the aortic pressure curve?
It represents the brief backflow of blood that closes the aortic valve after ventricular systole.
How does a pacemaker help patients with arrhythmias?
It delivers electrical impulses to regulate heart rate and rhythm.
