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Flashcards in Cardiac cycle Deck (13)
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What is a cardiac cycle?

All events that occur from the beginning of one heart beat to the beginning of the next


What occurs during diastole and systole?

-Diastole: the heart ventricles are relaxed and fill with blood
-Systole: the heart ventricles contract and pump blood into the: aorta (LV) and pulmonary artery (RV)


At a heart rate of 75bpm, how long does both the diastole and systolic phase last?

diastole = 0.5sec
systole= 0.3 sec
so diastole lasts almost twice as long as systole


What are the 5 events during the cardiac cycle?

-Passive Filling
-Atrial Contraction
-Isovolumetric ventricular Contraction
-Ventricular Ejection
-Isovolumetric ventricular Relaxation


Describe passive filling.

-Pressure in atria and ventricles close to zero
-AV valves open so venous return flows into the ventricles
-Aortic pressure ~ 80 mmHg, and aortic valve is closed
-Similar events happen in the right side of the heart, but the pressures (right ventricular and pulmonary artery) are much lower
-Ventricles become ~ 80% full by passive filling


What is atrial contraction ?

Completes the end diastolic volume and is represented in the ECG between the P-wave (atrial depolarisation) and the QRS wave


Describe isovolumetric ventricular contraction.

-Ventricular contraction starts after the QRS (signals ventricular depolarization) in the ECG
-Ventricular pressure rises
-When the ventricular pressure exceeds atrial pressure the AV VALVES SHUT
-This produces the FIRST HEART SOUND (LUB)
-The aortic valve is still shut, so no blood can enter or leave the ventricle
-The tension rises around a closed volume “Isovolumetric Contraction”
-The ventricular pressure rises very steeply


What produces the first heart sound?

The "LUB" is produced by the closure of mitral and tricupsid valves


Describe ventricular ejection?

-When the ventricular pressure exceeds aorta/pulmonary artery pressure
-Aortic/pulmonary valve open - Remember this is a silent event
-Stroke Volume (SV) is ejected by each ventricle, leaving behind the End Systolic Volume (ESV)
= 135 – 65 = 70 ml
-Aortic pressure rises
-The T-wave in the ECG signals ventricular repolarization
-The ventricles relax and the ventricular pressure start to fall
-When the ventricular pressure falls below aortic/pulmonary pressure: aortic/pulmonary valves shut
-This produces the SECOND HEART SOUND (DUB)
-The valve vibration produces the dicrotic notch in aortic pressure curve


What produces the second heart sound?

The "DUB" sound -When ventricular pressure falls below aortic/pulmonary pressure , the aortic/pulmonary valves shut


Describe the isovolumetric ventricular relaxation ?

-Closure of aortic/and pulmonary valves signals the start of the isovolumetric ventricular relaxation
-Ventricle is again a closed box, as the AV valve is shut
-The tension falls around a closed volume “Isovolumetric Relaxation”
-When the ventricular pressure falls below atrial pressure, AV valves open (Remember this is a silent event), and the heart starts a new cycle


Why does arterial pressure does not fall to 0?

Due to elastic properties of arteries , they stretch when contracted and when they recoil so recoiling moves blood forward


When does jugular venous pulse occur?

Occurs after right atrial pressure waves (indirect measurement ofd central venous pressure )