CVS - The Heart As A Pump

Question 1

What is the difference between resistance and capacitance vessels?

Answer 1

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.

Question 2

Which has the higher pressure - the systemic or pulmonary circulation?

Answer 2

Systemic circulation has high, while pulmonary has low.

Question 3

What is systole?

Answer 3

When the heart contracts and ejects blood from the ventricles

Question 4

What is diastole?

Answer 4

When the heart relaxes and the ventricles fill.

Question 5

What is the rough amount of blood pumped by each ventricle per beat?

Answer 5

About 70 ml

Question 6

Is a cardiac action potential relatively long or short?

Answer 6

Relatively long - lasts for duration of a single contraction of heart (around 280ms)

Question 7

Which valve regulates flow from left atrium to left ventricle?

Answer 7

Mitral valve

Question 8

Which valve regulates flow from right atrium to right ventricle?

Answer 8

Tricuspid valve

Question 9

Which valve regulates flow out of the right ventricle?

Answer 9

Pulmonary valve

Question 10

Which valve regulates flow out of the left ventricle?

Answer 10

Aortic valve

Question 11

How do the cusps of the mitral and tricuspid valves attach to papillary muscle?

Answer 11

Via chordae tendineae, which prevent inversion of valves on systole.

Question 12

Describe the sequence of electrical conduction in the heart.

Answer 12

• 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

Question 13

What are the seven stages of the cardiac cycle?

Answer 13

1) atrial contraction
2) isovolumetric contraction
3) rapid ejection
4) reduced ejection
5) isovolumetric relaxation
6) rapid filling
7) reduced filling

Question 14

When the heart rate increases, what happens to the length of systole and diastole?

Answer 14

Systole remains the same, diastole shortens

Question 15

What does a Wiggers diagram show?

Answer 15

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)

Question 16

What is the relationship between left ventricle volume and left ventricle pressure?

Answer 16

As pressure increases, volume decreases. Aortic pressure also increases simultaneously.

Question 17

What happens in phase 1 of heart contraction?

Answer 17

ATRIAL CONTRACTION

Atrial pressure rises due to atrial systole - this is called the ‘A wave’. Ventricular volume peaks.

Question 18

What happens in phase 2 of heart contraction?

Answer 18

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

Question 19

What happens in phase 3 of heart contraction?

Answer 19

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’)

Question 20

What happens in phase 4 of heart contraction?

Answer 20

REDUCED EJECTION

• repolarisation of ventricle causes rate of contraction to fall
• atrial pressure rises (‘V wave’)
• T-wave of ECG

Question 21

What happens in phase 5 of heart contraction?

Answer 21

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)

Question 22

What happens in phase 6 of heart contraction?

Answer 22

RAPID FILLING

• fall in atrial pressure after mitral valve opens (Y-descent)
• third heart sound (S3) present in children and occasionally (abnormally) in adults

Question 23

What happens in phase 7 of heart contraction?

Answer 23

REDUCED FILLING

• rate of filling slows as ventricle reaches inherent relaxed volume

Question 24

What is aortic valve stenosis?

Answer 24

• 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

Question 25

Give some causes of aortic valve stenosis.

Answer 25

- degenerative (senile calcification/fibrosis) - congenital - chronic rheumatic fever

Question 26

Give some causes of aortic valve regurgitation

Answer 26

- aortic root dilation | - valvular damage

Question 27

What is it called when a valve doesn't close all the way?

Answer 27

Regurgitation

Question 28

What is it called when a valve doesn't open enough?

Answer 28

Stenosis

Question 29

What are the effects of aortic valve regurgitation?

Answer 29

- blood flows back into LV during diastole, which increases stroke volume - systolic pressure increases, diastolic pressure decreases

Question 30

Give some symptoms of aortic valve regurgitation

Answer 30

- bounding pulse (head bobbing, Quinke's sign) | - LV hypertrophy

Question 31

Give some causes of mitral valve regurgitation

Answer 31

- Myxomatous degeneration can weaken tissue leading to prolapse - damage to papillary muscle - left sided heart failure - rheumatic fever

Question 32

How does mitral valve regurgitation cause LV hypertrophy?

Answer 32

Some blood leaks back into LA, which increases pre-load and can cause LV hypertrophy

Question 33

What is the main cause of mitral valve stenosis?

Answer 33

Rheumatic fever

Question 34

What does increased LA pressure due to mitral valve stenosis cause?

Answer 34

- pulmonary oedema, dyspnea and pulmonary hypertension which can lead to RV hypertrophy - LA dilation, which can lead to: - atrial fibrillation -> thrombus formation - oesophagus compression -> dysphagia