Physiology 3120 Lecture Notes - Vascular Resistance, Aortic Valve, Heart Valve

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26 Nov 2011
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Human Physiology
Monday, January 11, 2010
Cardiac Cycle
Ratio of stroke volume to end diastolic volume = ejection fraction
Normally about 60% of E.D.V. ejected in stroke volume
Venous capacitance (VC)
If VC decreases, volume of blood in ventricle increases
Relationship to pressure changes in ventricle
When ventricle begins to relax, very little blood is ejected (protodiastole)
When ejection is over, and the ventricle continues to relax, the high pressure in the aorta causes
momentary backflow of blood into the ventricle, which causes the semilunar valves to close
Aortic pressure
Diastolic = 80mmHg (doesn’t fall to 0 because of the resistance)
Systolic = 120mmHg
As blood enters the aorta as the ventricle contracts, pressure rises (depends not only on blood
volume, but also on peripheral vascular resistance)
Incisura: small hump in aortic pressure curve
Momentary backflow of blood, causing closure of the aortic valve
The pressure relationships are the same in the pulmonary artery, but the pressure are about 1/6
The sounds are caused by the closing of the heart valves (much more rapid than opening of the
valves), which cause vibrations of the surrounding fluid
1st sound
Ventricular pressure rises, and atrial pressure is low
Causes rapid closure of AV valves
2nd sound
Closure of SL valves
3rd sound
Not always present
Middle of diastole, when ventricle is almost fully filled
Believed to be due to small amounts of blood trickling into ventricle
Abnormal sounds in diseases
Aortic stenosis = valves stick together & can’t open well, so opening is narrow
During systole, blood jets through narrow opening of aortic valve, causing a
prolonged 1st sound
Mitral stenosis
Blood flowing into ventricle must jet through narrow opening, causing a
prolonged sound
Aortic regurgitation
During diastole, valves don’t work, so blood flows backward
Mitral regurgitation
Valvular lesions (caused by rheumatic fever)
Stenosis = damaged edges of valve leaflets stick together; narrow opening
Regurgitation = valve edges destroyed by scar tissue; fails to close properly
Function of Myocardial Cells