Cardiac Cycle Flashcards
Describe the 3 phases of pacemaker potentials.
Phase 4:
• Pacemaker potentials – the ‘funny current – If’
• If – hyperpolarisation-activated Na channel.
• Inward diffusion of Na ions – slow depolarisation.
Phase 0:
• Depolarisation - activation of voltage-gated Ca channels – Ca influx .
Phase 3:
• Repolarisation - activation of voltage-gated K channels - K efflux.
Describe the 5 phases of the AV action potentials.
Phase 0: Rapid Depolarisation
• Voltage-gated Na channels open leading to Na influx.
• Voltage-gated Ca channels (VGCCs) start to open slowly.
Phase 1: Early Repolarisation - Na channels close.
Phase 2: Plateau Phase
• VGCCs fully open - Ca influx.
• Voltage-gated K channels start to open slowly.
Phase 3: Rapid Repolarisation- VGCCs channels close + K channel open fully – K efflux.
Phase 4: Resting Phase
• Na-K pump – Na out, K in.
• Membrane impermeable to Na
• Membrane permeable to K
Describe the electrical conduction in the heart and how it spreads.
First electrical activity is generated in the SA node which spreads out via the gap junctions and causes the atria to contract simultaneously.
Electrical impulse reaches AV node (which is fibrous and insulating tissue), it causes a delay which allows correct filling of ventricles.
Then there is conduction which occurs rapidly through the bundle of His into the ventricles. Finally, conduction through the Purkinje fibres spreads rapidly throughout the ventricles causing contraction. Contraction begins at the apex.
What are the different waves/segments of an ECG?
In order
P Wave = Atrial depolarisation
PR Segment = AV node delay
QRS Complex = Ventricular depolarisation and simultaneous atrial depolarisation.
ST Segment = Ventricles are contracting and emptying
T Wave = Ventricular repolarisation
TP Interval = Ventricles are relaxing and filling
Describe the ventricular filling phase of the Cardiac Cycle and what position its in (i.e. first, second etc.)
Tricuspid and Mitral valves are open and so blood is flowing into ventricles. This happens because the pressure in the atrium is higher than in the ventricle. Ventricles will then stop relaxing and continue filling leading to an increase in pressure. Atrial contraction occurs as a final push of remaining blood.
This is the first phase of the cardiac cycle.
Describe the Isovolumetric contraction phase of the Cardiac Cycle and what position its in (i.e. first, second etc.)
Ventricles are full and so pressure is now higher than in the atria this leads to the tricuspid and mitral valves closing. All valves in the heart are closed and so ventricles are a closed chamber. Ventricles start contracting and therefore pressure increases.
This is the second phase of the cardiac cycle.
Describe the Ejection phase of the Cardiac Cycle and what position its in (i.e. first, second etc.)
Pressure in ventricles while they’re contracting increases to the point where it is higher than pressure in the vessels. This causes the semilunar valves to open leading to blood moving out of the ventricles. At the same time we have blood entering the atria.
This is the third phase of the cardiac cycle.
Describe the Isovolumetric relaxation phase of the Cardiac Cycle and what position its in (i.e. first, second etc.)
Blood is leaving the ventricles and this causes the pressure in the ventricles to become lower than the pressure pressure in the arteries leading to the loss of kinetic energy in the blood. Semilunar valves then close and you now have a closed chamber. Ventricles relax causing the pressure to further decrease. Meanwhile pressure in atria is increasing and becomes greater than in the ventricles causing the AV valves to open.
This is the fourth and last phase of the cardiac cycle
Briefly describe the left ventricular volume changes during the cardiac cycle.
At the beginning, during phase 1, we have rapid filling of the ventricles so volume increases quickly and then plateaus. When atrial contraction occurs the speed of filling is high for just a moment. During phase 2 we have no change in volume because it is isovolumetric. In phase 3 the aortic valve opens and this means there is a sudden, rapid emptying of the ventricles which also plateaus as the pressure difference becomes smaller. In phase 4 we have the end systolic volume which stays the same because this phase is isovolumetric as well.
What are the equations from SV and ejection fraction?
SV = EDV (normally 120ml) – ESV (normally 40ml) EF = SV/EDV
Why doesn’t the aortic valve close as soon as the pressure in the left ventricle becomes lower than in the aorta?
This is because the blood flow as momentum/kinetic energy, it may not be under the high pressure but it still has a high enough momentum to get out (although slower).
What is incisura?
A small increase in pressure as semilunar valves close.
What are the different phases in the right atrial and jugular venous pressure changes?
“A” wave first which is an increase in venous pressure caused by atrial contraction. Then we get the AV valves closing, pressure starts to reduce but as the valves swing back and close they give a brief increase in pressure in the great veins, this is called “C”.
Now we have “X” descent, this a big drop in atrial/venous pressure caused by contraction in the ventricles, leading to atria getting larger and reducing pressure in the atria.
The drop in pressure is followed by an increase as blood starts to flow into the atria, this is the “V” wave. Pressure returns enough that the AV valves start to open, blood leaves the atria and enters the ventricles so pressure decreases (“Y” descent).
What does the area of a ventricular pressure-volume loop tell us?
Stroke work
What are the potential sources off heart sounds?
Caused by vibrations induced by closure of the cardiac valves. But you may also hear other sounds, like vibrations in the ventricular chambers or turbulent flow through the valves.
