Cardiovascular Physiology Flashcards
What does the P wave represent on an ECG?
Atrial depolarisation
What does the T wave represent on an ECG?
Ventricular repolarisation
What does the QRS complex represent on an ECG?
Ventricular depolarization
What is a positive chronotrope?
Something that increases heart rate
What is a positive inotropy?
Something that increases the contractility of the heart
Where does nervous system regulation of the heart originate?
The cardiovascular centre of the medulla oblongata
What neurotransmitter does the vagus nerve release?
Acetylcholine
What is the effect of the PSNS on the heart?
Decreased heart rate
What is the effect of the SNS on the heart?
Increased heart rate
What is cardiac reserve?
The difference between the cardiac output at rest and the maximum cardiac output
How does hypothermia affect the heart?
Decreases heart rate
What is cardiac output?
The amount of blood ejected into the aorta per minute
How does hyperthermia affect the heart?
Increases heart rate
What is the equation for cardiac output?
CO = HR x SV
What is stroke volume?
The amount of blood ejected out of the ventricle each cardiac cycle
What is contractility?
The forcefulness of contraction
What is after-load?
The amount of work the heart must do to generate ventricular pressure sufficient to eject blood.
What is pre-load?
The stretch on the heart before in contracts
What 3 factors affect SV?
Preload, afterload, contractility
Describe the Frank-Starling law
The stretch of the ventricular walls as the ventricle fills determines how forceful the contraction is - the more the muscle fibres are stretched, the more forceful the contraction.
What is TPR?
The amount of force affecting resistance to blood flow throughout the circulatory system
Is the mean blood pressure in the aorta closer to the systolic or diastolic blood pressure?
Diastolic
What is the speed of conduction from the SA node through the Atrial muscle?
Slow, 0.5m/s
What is the speed of conduction through the AV node?
Very slow, 0.05m/s
What is the speed of conduction through the AV bundles and purkinje fibres?
Fast, 5m/s
What is the time of delay of the AP through the AV node to the ventricels?
100ms
What is the purpose of the delay in AP through the AV node?
Allows for the atria to contract before the ventricles to fill them with a bit more blood
Where is the SA node located, precisely?
Right atrial wall just inferior to the opening of the superior vena cava
Approximately how many APs does the SA node fire a minute?
100
What is the intrinsic heart rate of the SA node?
40-60 BPM
What is the size of the AP produced by the SA node (mV)
1.5mV
Where is the AV node located, precisely?
Interatrial septum, just anterior to the opening of the coronary sinus
What is the last part of the heart to contract?
Apex
What kind of junctions are between cardiac myocytes?
Gap
What causes the gradual depolarisation of pacemaker cells?
Leaky Na+ channels
Approximately how long is a pacemaker cell AP?
0.8 seconds
What ion causes depolarisation of ventricular myocytes?
Na+
What causes the plateau phase of a ventricular myocyte AP?
VG slow Ca2+ channels inflow and K+ outflow
What ion causes the repolarization of the cardiac myocytes?
K+
What is the ion that rushes into the pacemaker cells once threshold is reached?
Ca2+
What causes the repolarisation of the ventricular myocyte?
Ca2+ channels closing and more K+ channels opening
How long does a ventricular myocyte AP last?
300ms
What is the change in MP in the ventricular myocyte AP (mV)
-90mV to +30mV
What is the change in MP in the pacemaker cell AP (mV)
-60mV to +10mV
How long does the depolarisation of ventricular myocytes take?
1-2ms
How long does the plateau phase of ventricular myocyte APs last?
200ms
How long is the repolarization phase of ventricular myocyte APs?
20-50ms
What is the refractory period?
The time in which a second AP cannot be triggered
Why is it good that the cardiac refractory period last longer than the normal AP?
To prevent tetanus from occuring
Do cardiac action potentials have after-hyperpolarisation phases?
No