Cardiac cycle Flashcards
1
Q
Define the SA node?
A
A group of cells located in the wall of the right atrium
2
Q
Define the characteristics of the SA node? (3pts)
A
- Ability to spontaneously produce an action potential that travels through the heart via the electrical conduction system
- It sets the rhythm of the heart and is known as the hearts natural pacemaker.
- The rate of each action potential production and therefore heart rate is influenced by the nerves that supply it.
3
Q
Define the AV node?
A
Is a part of the electrical conduction system of the heart. It electrically connects the right atrium and right ventricle delaying impulses so that atria have time to eject their blood into ventricles before ventricular contraction.
4
Q
Describe the sino-atrial node? (2pts)
A
- There is a resting negative voltage in the cell interior as compared to the cell exterior ranging from -40 to -80mv
- Normally there is high K+ inside and high Na+ and Cl- outside
- Sodium-potassium pump uses ATP to transport 3 sodiums ions out of the cell and 2 Potassium ions in.
5
Q
Describe the phases? (3pts)
A
- Phase 4 pacemaker- the funny current. not a genuine resting potential because it is unstable.
- Phase 0- voltage gated calcium channels open leading to calcium influx as calcium ions enter the cell. This causes rapid depolarisation.
- Phase 3- Repolarisation. the activation of K+ channels causes K+ out-flux.
6
Q
Describe atrial and ventricular muscle action potentials? (4pts)
A
- Phase 0= rapid depolarisation. Receives depolarization stimulus from SA node. This causes voltage gated Na+ channels to open and Na+ influx.
- Phase 1= early repolarisation. Na+ channels close beginning to repolarise
- Phase 2= Plateau phase. Voltage gated calcium channels will fully open causing an influx of calcium. This halts repolarisation.
- Phase 3= Rapid depolarisation. Ca2+ channels close and K+ channels open fully so K+ efflux occurs.
- Phase 4= Resting phase. Stable Na+/ K+ pimp. 3NA+ out and 2K+ in. The membrane is slightly impermeable to Na+ and is slightly permeable to K+.
7
Q
Describe electrical conduction through the heart? (4pts)
A
- Electrical activity is generated in the SA node which spreads out vida gap junctions into atria
- At the AV nose, conduction is delayed to allow correct filing of ventricles with blood
- Conduction occurs rapidly through the bundles of HIS into ventricles
- Conduction through Purkinje fibres spreads quickly throughout the ventricles.
8
Q
Where does ventricular contraction begin?
A
At the apex
9
Q
Describe an ECG ? (6pts)
A
- P wave= atrial depolarisation and contraction
- Pr segment= AV noval delay
- QRS complex= ventricular depolarization contraction. Atria repolarises simultaneously
- ST segment= ventricles contracting and emptying
- T wave= ventricular repolarisation
- TP interval= ventricles are relaxing and filling
10
Q
Name 5 cardiac cycle principles? (5pts)
A
- Electrical activity is generated at the SA node and conducted throughout the heart
- Electrical activity is converted into myocardial contraction which creates pressure changes within chambers
- Blood flows from an area of high pressure to an area of low pressure unless the flow is blocked by a valve
- The valve opens and closes depending on pressure changes in the chambers
- Events on the right and left sides of the heart are the same but pressure is lower on the right side of the heart.
11
Q
Name the stages in the cardiac cycle? (3pts)
A
- Cardiac diastole
- Relaxation of the heart muscles
- Blood returns to the heart and begins to fill the atria and the ventricles
- Low pressure in the ventricles allows the miral and tricuspid valves to open and the ventricles fill with blood.
- Atrial systole
- Atrial contraction causes blood to move into relaxed ventricles
- As the ventricles fill the increase in pressure in the ventricles forces mitral and tricuspid valves to close
- Ventricular systole
- The ventricles enter systole and begin contracting
- After a period of isovolumetric contraction pressure rises sufficiently to open aortic and pulmonary valves and blood is ejected from the ventricles.
12
Q
Describe left ventricle pressure changes? ( 5pts)
A
- Contraction of the left atrium pushes blood into the relaxed ventricle. Once the ventricle is full its pressure rises slightly and forces the mitral valve to close
- Pressure rises during isovolumetric contraction of ventricle.
- When ventricle pressure is higher than the aorta the aortic valve is pushed open and blood is ejected from the ventricle
- Ventricle empties and once its pressure is less than the aorta the aortic valve closes. This is followed by isovolumetric relaxation and large pressure drop below that of atrium causing mitral valve to open.
- Blood flows into the relaxed heart in preparation for another atrial systole.
13
Q
Explain the ventricular pressure-volume loop? (4pts)
A
- A= Diastole is occurring. The ventricles are relaxed and filling so the pressure remains low and the volume of blood is increasing
- B= end diastolic volume. The mitral valve closes and ventricle contracts. The volume doesn’t change as both mitral valves and aortic valves are closed but pressure increases.
- C= The pressure begins high enough to force aortic valves to open and blood begins to leave the ventricle. The volume decreases as pressure continues to rise because the heart is still contracting
- D= As the ventricle empties the aortic valve closes and the ventricles relaxes so the pressure falls dramatically.
14
Q
Describe heart sounds?
A
- S1- LUB- Closure of tricuspid/ mitral valves at the beginning of ventricular systole
- S2- DUB- Closure of aortic/ pulmonary valves ( semilunar valves) at the end of the ventricular systole.
- S3- occasional. it is turbulent blood flow into the ventricles. It is detected during near the end of the first 1/3 diastole especially in older people
- S4- Pathological in adults- forceful atrial contraction against a stiff ventricle
