The cardiac cycle (CVS5) Flashcards
1
Q
when does the heart normally produce sound
A
normally the heart valves produce a sound when they shut, they don’t normally produce a sound when they open
2
Q
what is the cardiac cycle
A
- refers to all events that occur from the beginning of one heart beat to the beginning of the next
- the orderly depolarization/repolarization sequence triggers a recurring cardiac cycle of atrial and ventricular contractions and relaxations
3
Q
diastole
A
the heart ventricles are relaxed and fill with blood
4
Q
systole
A
the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery (RV)
5
Q
approximate period of ventricular diastole/systole at heart rate of 75bpm
A
- ventricular diastole = ~0.5seconds
- ventricular systole = ~0.3seconds
6
Q
events during the cardiac cycle
A
- passive filling
- atrial contraction
- isovolumetric ventricular contraction
- ventricular ejection
- isovolumetric ventricular relaxation
7
Q
- passive filling
A
- 1st step in cardiac cycle
- pressure in atria and ventricles close to zero
- AV valves open so venous return flows into the ventricles
- aortic pressure= ~80mmHg, and aortic valve is closed
- similar events happen in the right side of the heart, but the pressures (right ventricular and pulmonary artery) are much lower
- ventricles become ~80% full by passive filling
8
Q
2.atrial contraction
A
- 2nd step in cardiac cycle
- the P wave in the ECG signals atrial depolarization
- the atria contracts between the P wave and the QRS
- atrial contraction complete the end diastolic volume (~130ml in resting normal adult) - the end diastolic pressure is few mmHg
9
Q
value of end diastolic volume in resting normal adult
A
~130ml
10
Q
3.isovolumetric ventricular contraction
A
- 3rd step of cardiac cycle
- ventricular contraction starts after the QRS (signals ventricular depolarization) in the ECG
- ventricular pressure rises
- when the ventricular pressure exceed atrial pressure the AV valves shut, which produces the first heart sound
- the aortic valve is still shut, so no blood can enter or leave the ventricle
- the tension rises around a closed volume ‘isovolumetric contraction’
- the ventricular pressure rises very steeply
11
Q
4.ventricular ejection
A
- 4th step of the cardiac cycle
- when the ventricular pressure exceeds aorta/pulmonary artery pressure
- aortic/pulmonary valve open (this is a silent event)
- stroke volume (SV) is ejected by each ventricle, leaving behind the end systolic volume (ESV)
- SV=EDV-ESV (=135-65=70ml)
- aortic pressure rises
- T wave in the ECG signals ventricular repolarization
- ventricles relax and the ventricular pressure starts to fall
- when the ventricular pressure falls below aortic/pulmonary pressure, the aortic/pulmonary valves shut (this produces the second heart sound)
- the valve vibration produces the dicrotic notch in the aortic pressure curve
12
Q
5.isovolumetric ventricular relaxation
A
- 5th step in cardiac cycle
- closure of aortic and pulmonary valves signals the start of isovolumetric ventricular relaxation
- ventricle is again a closed box, as the AV valve is shut
- the tension falls around a closed volume ‘isovolumetric relaxation’
- when the ventricular pressure falls below atrial pressure, the AV valves open (this is a silent event), and the heart starts a new cycle
13
Q
first heart sound
A
- S1
- caused by closure of mitral and tricuspid valves
- sounds like a lub
- signals the start/beginning of systole
14
Q
second heart sound
A
- S2
- caused by the closure of aortic and pulmonary valves
- sounds like a dub
- signals the end of systole and beginning of diastole
15
Q
how does the arterial pressure not fall to zero during diastole
A
- Elastic properties of arteries; aorta can expand when blood is ejected into it and when the heart relaxes they recoil back which keeps pushing the blood forward, maintaing the pressure in the aorta unlike the pressure in the ventricles which falls to 0 during diastole
- pressure within the heart falls to 0 during diastole but pressure remains in arteries
