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Lecture 14

PSL201Y1 Lecture Notes - Lecture 14: Diastole, Circulatory System, Pulmonary Vein

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Michelle French

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PSL201 Lecture 14 Reading Notes; Cardiovascular Physiology 3
The Cardiac Cycle- Integrated Events in Cardiac Function
- One event is dependent upon the others
- Contraction produces pressure changes that leads to blood flow
- Blood flows from high pressure to low pressure
- Events on the right side are the same as the left side but the pressures are lower on the right side
Cardiac Cycle Terminology
- Diastole: rest cycle where the heart fills
- Systole: active cycle where the heart empties
- Isovolumic: volume doesn’t hange ut pressure does; applies to oth relaxation and ontration
Systole and Diastole Are Not Equal
- Most of the cardiac cycle is spend in diastole
- Longer diastole gives heart adequate time to fill with blood and gives heart muscle more time to
relax preventing fatigue
Cardiac Cycle Phase 1- Ventricular Filling
- During mid to late diastole blood returning to the heart via the systemic and pulmonary veins enters
the relaxed atria and passes through the AV valves and into the ventricles under its own pressure
Venous return (blood returning from veins to heart) occurs because pressure in veins is greater than
in the atria
- Later in diastole the atria contract driving more blood to ventricles (ventricular filling), shortly after
the aria relax and systole begins
Cardiac Cycle Phase 2: Isovolumetric Contraction
- Beginning of systole, ventricles contract which raises pressure within them
When ventricular pressure exceeds atrial pressure the AV valves close; semilunar valves remain close
because ventriular pressure is’t high eough = o lood flo through etriles eause ales
remain close
- Phase 2 ends when ventricular pressure is great enough to force open the semilunar valves so blood
can leave the ventricles
Cardiac Cycle Phase 3: Ventricular Ejection
- Remainder of systole, blood is ejected into the aorta and pulmonary arteries through the open
semilunar valves and ventricular volume falls
- During ventricular ejection (blood exits ventricles), ventricular pressure rises to a peak and begins to
- When it falls below aortic pressure the semilunar valves close, ending ejection and making the
beginning of diastole
Cardiac Cycle Phase 4: Isovolumetric Relaxation
- During early diastole, the ventricular myocardium is relaxing; some blood present in ventricles and
remains under pressure because takes time for tension in the ventricular muscle to wane
- Ventricular pressure is too low to keep semilunar valves open and too high for AV valves to open so
it’s alled isooluetri relaxatio phase
- Once ventricular pressure is less than atrial pressure, it allows the AV valves to open and blood
enters the ventricles and phase 1 restarts
Heart Sounds
- First sound (lubb) happens at the beginning of systole (phase 2)
- Second sound (dubb) happens at the beginning of diastole (phase 4)
- Sounds happen because of the blood rushing through the valves as they are narrowing about to
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