Cardiac Cycle Flashcards
(24 cards)
What generates the S1 heart sound?
Closure of the AV valves
Mitral valve (left) and tricuspid valve (right)
What generates the S2 heart sound?
Closure of the semi-lunar valves
Aortic (left) and pulmonary (right)
How is systole identified on auscultation?
The gap between S1 and S2.
What generates the S3 heart sound?
Passive filling of the ventricles (early diastole)
In early diastole, the ventricles relax and rapidly fill with blood, causing the walls to ‘vibrate’.
What generates the S4 heart sound?
Active filling of the ventricles (late diastole)
Toward the end of diastole, when the ventricles are mostly full (and therefore stiff and non-compliant), the atria contract to force the remaining blood in, causing the ventricles to ‘creak’.
What events of the cardiac cycle are represented by the P wave, QRS complex, and T wave on an ECG?
P wave: atrial depolarization
QRS complex: ventricular depolarization
T wave: ventricular re-polarization
The SA node fires spontaneously because of the rhythmic inflow of ____ and ____ ions and outflow of ____ ions.
inflow of Ca2+ and Na+ ions
outflow of K+ ions
The influx of calcium and sodium ions causes the L atrium to depolarize (i.e. become more positive), and the outflow of potassium ions facilitates its repolarization (i.e. return to -60mV)
Which ion is involved in the funny current (If)?
Na+
The neurotransmitters of the sympathetic nervous system are ________ and ________.
Noradrenaline and adrenaline
How does the sympathetic nervous system increase heart rate?
Opens more calcium and funny channels
Noradrenaline and adrenaline open more calcium and funny channels, resulting in an increased influx of Ca2+ and Na+ and therefore an increased rate of SA node firing.
The main neurotransmitter of the parasympathetic nervous system is _______________.
Acetylcholine (ACh)
How does the parasympathetic nervous system decrease heart rate?
Closes calcium and funny channels opens more potassium channels
Acetylcholine (ACh) closes Ca2+ and funny channels AND opens more K+ channels, resulting in a hyperpolarized cell membrane. This makes it difficult for the SA node to fire again, as it is further away from the level of positivity needed to depolarize and start an action potential.
Sympathetic effects on the SA and AV node are via ____ receptors.
Beta-1 receptors
Vagal effects of the SA and AV node are via ____________ receptors.
Muscarinic (M2) receptors
The vagus effects on the heart are mediated through the parasympathetic nervous system.
Purkinje and myocardial action potentials rely on ____ to initiate an action potential and ____ to prolong the action potential and initiate excitation-contraction coupling.
Na+ influx to initiate it
Ca2+ influx to prolong it and initiate excitation-contraction coupling
How does the sympathetic nervous system increase contractility?
Increases the amount of Ca2+ available to initiate myocardial contractions
Noradrenaline binds to B1 receptors –> increased Ca2+ –> Ca2+ binds Troponin C and initiates myocardial contractions
How does the sympathetic nervous system’s effect on contractility impact diastole?
Enhances myocardial relaxation
Ca2+ detachment from Troponin C initiates diastole
SERCA ATPase pumps Ca2+ back into sarcoplasmic reticulum —> enhances myocardial relaxation
How does inspiration affect preload?
Increases preload
Increased negative pressure —> increased vena cava filling —> increased volume going to LA
What is the basic function of the Frank-Starling mechanism?
Increase contractility in response to increased preload
Increased preload —> increased end-diastolic volume —> increased stroke volume
How does the Frank-Starling differ from contractility?
Increases when preload increased
Does not require ATP
Not directly affected by sympathetic NS stimulation
What is afterload?
Resistance of a tube/blood vessel varies inversely to the radius
How does Poiseuille’s law relate to afterload?
Small change in vasculature diameter has a significant impact on resistance/blood pressure
R = 1/r4
What is cardiac compliance?
Distensibility of the heart
Which nerve is closely involved with parasympathetic regulation of the heart?
Vagal nerve
