the cardiac cycle Flashcards
what are the 5 steps in the cardiac cycle?
The Cardiac Cycle:
[1] Late diastole —both sets of chambers are relaxed and ventricles fill passively.
[2] Atrial systole —atrial contraction forces a small amount of additional blood into the ventricles.
[3] Isovolumic ventricular contraction—ventricular contraction pushes AV valves closed & not enough pressure to open semilunar valves.
[4] Ventricular ejection—as ventricular pressure rises and exceeds the pressure in the arteries, the semilunar valves open and blood is ejected.
[5] Isovolumic ventricular relaxation—as ventricles relax, pressure in ventricles falls. Blood flows back into the cusps of semilunar valves and snaps them closed.
what are the semilunar valves?
aortic valve and pulmonary valve.
what is the minimum blood volume in ventricles?
The minimum blood volume in ventricles = end-systolic volume (ESV) seen in the Isovolumic ventricular relaxation stage
→ 60ml of blood
what is the maximum blood volume in the ventricles?
Maximum blood volume in ventricles = end-diastolic volume (EDV) seen in Isovolumic ventricular contraction stage
→ 140ml of blood
state the meaning of systolic and diastolic pressure and their values:
Systolic pressure is the peak arterial pressure = 120 mmHg
Diastolic pressure is the minimum arterial pressure = 80 mmHg
state what diastole and systole mean:
diastole = filling phase
systole = ejection phase
what happens to the mitral and atrial valves when the left ventricle changes?
When the LV pressure exceeds the pressure inside the left atrium, the mitral valve closes.
When the LV pressure is below the pressure inside the left atrium, the mitral valve opens.
When the LV pressure is above the aortic pressure, the aortic valve opens.
When the LV pressure is below the aortic pressure, the aortic valve closes.
define the pulse pressure:
the difference between the systolic and diastolic pressure.
define the mean arterial pressure:
the average arterial pressure throughout the cardiac cycle.
- the driving force pushing blood through the circulation
define the atrial pressures of an ECG:
a-wave → atrial contraction, which occurs right after the P wave on ECG.
c-wave → rises when ventricles contract, causing the mitral valve to bulge into the atrium, and descends when the aortic valve opens.
v-wave → blood flowing from the lung into the left atrium while the ventricles contract.
what is the ejection fraction?
the stroke volume (SV) divided by the end-diastolic volume (EDV)
EF = SV/EDV = usually around 2/3 in a healthy heart.
define the isometric contraction period:
the time between the closure of the atrioventricular valves and the opening of the semilunar valves.
Involves pressure going up in ventricles above the pulmonary trunk/aorta which pushes the semilunar valves open.
define the isometric relaxation period:
the time between the closure of the atrioventricular valves and the opening of the semilunar valves.
Involves pressure going up in ventricles above the pulmonary trunk/aorta which pushes the semilunar valves open.
what happens when the pressure within the ventricles drops below pressure in both the pulmonary trunk and aorta?
blood flows back toward the heart,
producing the dicrotic notch which is a small dip seen in blood pressure tracings.
when does the rapid and slow ejection phase occur?
rapid ejection phase occurs when the pressure rises in the ventricles enough to open the semilunar valves.
Occurs at the beginning of systole and involves a very quick drop in volume.
slower ejection phase occurs when the pressure falls in the ventricles until the semilunar valves close.
Occurs at the end of systole and involves a slower drop in volume.
