CVS - The Heart As A Pump Flashcards
What is the difference between resistance and capacitance vessels?
Resistance vessels - restrict blood flow to drive supply to hard to perfuse areas of the body, usually arteries.
Capacitance vessels - enable system to vary amount of blood pumped around body, usually veins.
Which has the higher pressure - the systemic or pulmonary circulation?
Systemic circulation has high, while pulmonary has low.
What is systole?
When the heart contracts and ejects blood from the ventricles
What is diastole?
When the heart relaxes and the ventricles fill.
What is the rough amount of blood pumped by each ventricle per beat?
About 70 ml
Is a cardiac action potential relatively long or short?
Relatively long - lasts for duration of a single contraction of heart (around 280ms)
Which valve regulates flow from left atrium to left ventricle?
Mitral valve
Which valve regulates flow from right atrium to right ventricle?
Tricuspid valve
Which valve regulates flow out of the right ventricle?
Pulmonary valve
Which valve regulates flow out of the left ventricle?
Aortic valve
How do the cusps of the mitral and tricuspid valves attach to papillary muscle?
Via chordae tendineae, which prevent inversion of valves on systole.
Describe the sequence of electrical conduction in the heart.
- pacemaker cells in SINOATRIAL NODE generate an action potential
- activity spreads over ATRIA
- reaches the AV NODE where it is delayed for 120 ms
- spreads down SEPTUM between ventricles
- spreads through VENTRICULAR MYOCARDIUM from inner to outer epicardial surface
- ventricle contracts from BASE up
What are the seven stages of the cardiac cycle?
1) atrial contraction
2) isovolumetric contraction
3) rapid ejection
4) reduced ejection
5) isovolumetric relaxation
6) rapid filling
7) reduced filling
When the heart rate increases, what happens to the length of systole and diastole?
Systole remains the same, diastole shortens
What does a Wiggers diagram show?
It illustrates the co-ordination of the cardiac cycle, using:
- aortic pressure
- left ventricular pressure
- left atrial pressure
- left ventricular volume
- ECG
- phonocardiogram (heart sounds)
What is the relationship between left ventricle volume and left ventricle pressure?
As pressure increases, volume decreases. Aortic pressure also increases simultaneously.
What happens in phase 1 of heart contraction?
ATRIAL CONTRACTION
Atrial pressure rises due to atrial systole - this is called the ‘A wave’. Ventricular volume peaks.
What happens in phase 2 of heart contraction?
ISOVOLUMETRIC CONTRACTION
- mitral valve closes, but aortic valve still closed so volume does not change
- first heart sound (S1) caused by closing of valves
- QRS complex in ECG and C wave in atrial pressure curve
What happens in phase 3 of heart contraction?
RAPID EJECTION
- ventricular pressure higher than in aorta so aortic valve opens
- ventricles contract
- atrial pressure initially decreases as atrial base is pulled downwards as ventricle contracts (‘X descent’)
What happens in phase 4 of heart contraction?
REDUCED EJECTION
- repolarisation of ventricle causes rate of contraction to fall
- atrial pressure rises (‘V wave’)
- T-wave of ECG
What happens in phase 5 of heart contraction?
ISOVOLUMETRIC RELAXATION
- brief backflow of blood into ventricle is stopped by aortic valve (dicrotic notch)
- rapid decline in ventricular pressure but volume remains constant as all valves are closed (these cause second heart sound - S2)
What happens in phase 6 of heart contraction?
RAPID FILLING
- fall in atrial pressure after mitral valve opens (Y-descent)
- third heart sound (S3) present in children and occasionally (abnormally) in adults
What happens in phase 7 of heart contraction?
REDUCED FILLING
- rate of filling slows as ventricle reaches inherent relaxed volume
What is aortic valve stenosis?
- valve doesn’t open enough, so less blood can get through
- can lead to increased LV pressure -> LV hypertrophy
- can lead to left sided heart failure -> syncope, angina
- shear stress can damage erythrocytes
