The Cardiac Cycle

Question 1

Cardiac Output

Answer 1

Stroke volume x heart rate

Question 2

End-diastolic volume (EDV)

Answer 2

Volume of blood in the heart at the end of diastole (100ml)

Question 3

End-systolic volume (ESV)

Answer 3

Volume of blood in the heart at the end of systole (40ml)

Question 4

Ejection fraction

Answer 4

Around 60ml is ejected.

- SV/EDV = 60/100 = 60%

Question 5

Stroke volume

- dependent on 3 factors

Answer 5

EDV - ESV

1. Contractility
2. Preload:
3. Afterload

Question 6

Contractility

Answer 6

Force of contraction of the myocardium

Question 7

Preload

Answer 7

Degree of stretch of cardiac myocytes at the end of diastole (Starling’s forces)

Question 8

Afterload

Answer 8

Resistance that the ventricle must overcome to eject blood from the heart

• vascular pressure: pressure in heart > pressure in elastic arteries
• valve damage: stenosis reduces CO

Question 9

Late diastole

Answer 9

Both sets of chambers are relaxed, and ventricles fill passively

• rapid filling phase
• slower filling phase

Question 10

Atrial systole

Answer 10

Atrial contraction forces a small amount of additional blood into ventricles

Question 11

Isovolumic ventricular contraction

Answer 11

First phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semilunar valves

Question 12

Ventricular ejection

Answer 12

Ventricular pressure rises and exceeds pressure in arteries.
Semilunar valves open and blood is ejected
- rapid ejection phase
- slower ejection phase

Question 13

Isovolumic ventricular relaxation

Answer 13

Ventricles relax
Pressure in ventricles falls
Blood flows back into cusps of semilunar valves and snaps them closed

Question 14

Pressure-volume loop

Answer 14

1 loop = 1 heartbeat

Question 15

Phonocardiogram

Answer 15

Sounds produced by turbulence in the blood

• valves closing
• rapid blood flow
• stenosis/regurgitation