The Heart as a Pump Flashcards
How does pulmonary arterial pressure differ from systemic pressure?
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
Why is it important that both pulmonary and systemic circuits have the same cardiac output?
Blood would gradually accumulate in one side of heart
How is blood flow calculated?
Flow = pressure/resistance (for both circuits separately)
What is the tricuspid valve?
Right AV valve
What is the bicuspid/mitral valve?
Left AV valve
What is the pulmonary valve?
Semilunar valve between right ventricle and pulmonary artery
What is the aortic valve?
Semilunar valve between the left ventricle and the aorta
What is the role of papillary muscles?
First to contract in ventricular systole to pull chordae tendinae to close valves
What are ‘chordae tendinae’?
Fibrous tendons which attach to valves to keep them in position (also attached to papillary muscles)
Describe the valve sequence of the left side of the heart in a normal cardiac cycle
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
How are ventricles usually filled?
As a result of the elastic recoil of ventricular wall during diastole
What causes heart sounds?
Turbulent blood flow either due to normal valve closure or pathology of valves
Describe the ‘lubb’/S1 heart sound
Due to closure of AV valves followed by opening of semilunar valves
Describe the ‘dupp’/S2 heart sound
Closure of semilunar valves followed by opening of AV valves
Describe the S3 heart sound
Faint, low-pitched sound and can be indicative of serious heart damage in adults, but is relatively common in children and young adults
Where would you auscultate the aortic semilunar valve?
Left of sternum at 2nd intercostal space
Where would you auscultate the pulmonary semilunar valve?
Right of sternum at 2nd intercostal space
Where would you auscultate the bicuspid/mitral valve?
Mid-axillary line of the 5th intercostal space
Where would you auscultate the tricuspid valve?
Just to right of sternum at bottom of 5th intercostal space
State Starling’s law
Ventricular contractile force increase with increased end diastolic volume
Explain Starling’s law
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
When does Starling’s law fail?
If ventricle expands beyond certain volume the ventricles become overstretched and weaken (heart failure)
Define ‘preload’
Degree of stretching of ventricle during diastole
Define ‘afterload’
The effective flow impedence/resistance of the aorta and large arteries
What mediated venous return to the heart?
One-way valves, muscular pumps (contraction of muscle –> propels blood), thoraco-abdominal pump
What causes JVP?
When right atrium contracts, backpressure occurs (due to absence of valves) in the jugular vein which can be felt as feint pulse
What is preload proportional to?
End diastolic volume
What is the consequence of a large afterload?
Causes longer period of ventricular systole before semilunar valves open, and shorter ejection duration –> smaller SV and larger residual volume
What is the thoraco-abdominal pump?
In inspiration; thoracic cavity pressure reduces –> pulls blood into IVC
Expiration; thoracic pressure increases and blood is forced into right atrium
