The Heart as a Pump

Question 1

How does pulmonary arterial pressure differ from systemic pressure?

Answer 1

It’s lower as TVR in pulmonary vascular bed is much lower –> less pressure needed from R side to push same CO through pulmonary circuit

Question 2

Why is it important that both pulmonary and systemic circuits have the same cardiac output?

Answer 2

Blood would gradually accumulate in one side of heart

Question 3

How is blood flow calculated?

Answer 3

Flow = pressure/resistance (for both circuits separately)

Question 4

What is the tricuspid valve?

Answer 4

Right AV valve

Question 5

What is the bicuspid/mitral valve?

Answer 5

Left AV valve

Question 6

What is the pulmonary valve?

Answer 6

Semilunar valve between right ventricle and pulmonary artery

Question 7

What is the aortic valve?

Answer 7

Semilunar valve between the left ventricle and the aorta

Question 8

What is the role of papillary muscles?

Answer 8

First to contract in ventricular systole to pull chordae tendinae to close valves

Question 9

What are ‘chordae tendinae’?

Answer 9

Fibrous tendons which attach to valves to keep them in position (also attached to papillary muscles)

Question 10

Describe the valve sequence of the left side of the heart in a normal cardiac cycle

Answer 10

Start of systole - left ventricle starts to contract so mitral/bicuspid valve closes
During systole - pressure increase causes aortic valve to open
End of systole - aortic valve closes
Pressure near zero - mitral valve reopens

Question 11

How are ventricles usually filled?

Answer 11

As a result of the elastic recoil of ventricular wall during diastole

Question 12

What causes heart sounds?

Answer 12

Turbulent blood flow either due to normal valve closure or pathology of valves

Question 13

Describe the ‘lubb’/S1 heart sound

Answer 13

Due to closure of AV valves followed by opening of semilunar valves

Question 14

Describe the ‘dupp’/S2 heart sound

Answer 14

Closure of semilunar valves followed by opening of AV valves

Question 15

Describe the S3 heart sound

Answer 15

Faint, low-pitched sound and can be indicative of serious heart damage in adults, but is relatively common in children and young adults

Question 16

Where would you auscultate the aortic semilunar valve?

Answer 16

Left of sternum at 2nd intercostal space

Question 17

Where would you auscultate the pulmonary semilunar valve?

Answer 17

Right of sternum at 2nd intercostal space

Question 18

Where would you auscultate the bicuspid/mitral valve?

Answer 18

Mid-axillary line of the 5th intercostal space

Question 19

Where would you auscultate the tricuspid valve?

Answer 19

Just to right of sternum at bottom of 5th intercostal space

Question 20

State Starling’s law

Answer 20

Ventricular contractile force increase with increased end diastolic volume

Question 21

Explain Starling’s law

Answer 21

Increase in preload (blood delivered to ventricles) causes greater dilation of ventricular walls (due to greater EDV) and therefore greater recoil –> greater force of contraction –> greater SV –> greater CO

Question 22

When does Starling’s law fail?

Answer 22

If ventricle expands beyond certain volume the ventricles become overstretched and weaken (heart failure)

Question 23

Define ‘preload’

Answer 23

Degree of stretching of ventricle during diastole

Question 24

Define ‘afterload’

Answer 24

The effective flow impedence/resistance of the aorta and large arteries

Question 25

What mediated venous return to the heart?

Answer 25

One-way valves, muscular pumps (contraction of muscle –> propels blood), thoraco-abdominal pump

Question 26

What causes JVP?

Answer 26

When right atrium contracts, backpressure occurs (due to absence of valves) in the jugular vein which can be felt as feint pulse

Question 27

What is preload proportional to?

Answer 27

End diastolic volume

Question 28

What is the consequence of a large afterload?

Answer 28

Causes longer period of ventricular systole before semilunar valves open, and shorter ejection duration –> smaller SV and larger residual volume

Question 29

What is the thoraco-abdominal pump?

Answer 29

In inspiration; thoracic cavity pressure reduces –> pulls blood into IVC
Expiration; thoracic pressure increases and blood is forced into right atrium