Cardiac cycle

Question 1

Phase 1 atrial systole

Answer 1

Blood enters ventricles when atria are relaxed during diastole
Last 20% occurs during systole = atrial boost
Atria contract simultaneously > blood pressure increases which opens AV valves
When atria contract blood is forced backwards into the superior and inferior vena cava as there are no one way valves to prevent back flow

Question 2

EDV

Answer 2

Volume of blood in the ventricle at the end of filling

Question 3

Phase 2 isovolumetric contraction

Answer 3

First phase of ventricular systole
Ventricles contract to push upwards on AV valves so they stay closed however not enough pressure is generated to open the SL valves
There is no change in vol but rapid increase in pressure as chamber is closed

Question 4

Phase 3 ventricular ejection

Answer 4

Ventricular pressure > arterial pressure, SL valves open
High pressure blood forced into the arteries displacing low pressure blood that fills them
The ventricular blood enters the aorta faster than blood can leave the arterial tree therefore arterial pressure rises + elastic expansion + collagen maintains shape
Ventricles relax, pressure falls below aortic, brief backflow closes aortic valve close

Question 5

Dicrotic notch

Answer 5

Valve closure gives rise to a brief increase in arterial pressure

Question 6

ESV

Answer 6

Final volume in ventricles

Question 7

Phase 4 isovolumetric relaxation

Answer 7

Aortic and pulmonary valves are both closed
Each ventricle briefly becomes a closed chamber
Elastic recoil of relaxing myocardium causes ventricular pressure to rapidly fall
Ends when pressure falls below atrial pressure meaning pressure difference pushes open AV valves

Question 8

Phase 5 late diastole

Answer 8

Both atria and ventricles relax
Blood enters atria via pulmonary vein and vena cava
Initial ventricle filling is rapid > ventricles still in elastic recoil hence have low pressure and suck blood in