Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

All events associated with the flow of blood through the heart during one heart beat

Question 2

How long does one cycle last?

Answer 2

0.8 sec

Question 3

What does cardiac cycle involve?

Answer 3

 Series of coordinated Electrical and mechanical events resulting in volume and pressure changes within the heart

Question 4

What are the left valves?

Answer 4

• Bicuspid / mitral valve

- Aortic valve

Question 5

What does contraction of atria follow?

Answer 5

Depolarisation

Question 6

What represents contraction of atria on ECG?

Answer 6

P wave

Question 7

Why does atrial systole only contribute 20-30% of blood to ventricles?

Answer 7

At start of atrial systole, ventricles are normally filled with 70-80% capacity due to passive inflow during diastole

Question 8

What direction do atrial muscles contract?

Answer 8

Contract from superior portion of atria toward atrioventricular septum

Question 9

What happens to pressure in atria during atrial systole?

Answer 9

Pressure rises within atria and blood pumped into ventricles through open AV valve

Question 10

What does ventricular systole follow?

Answer 10

Depolarisation of ventricles

Question 11

What represents ventricular systole on ECG?

Answer 11

QRS complex

Question 12

What 2 phases can ventricular systole be divided into?

Answer 12

1. Isovolumic contraction (1st phase)

2. Ventricular ejection (2nd phase)

Question 13

What happens in isovolumic contraction of ventricles and why does this mean volume of blood in chamber stays constant?

Answer 13

Pressure within chamber rises but not high enough to open SL valves and eject blood

Since blood is not being ejected from the ventricles at this early stage, the volume of blood within the chamber remains constant

Question 14

Why does isovolumic contraction of ventricles cause AV valves to close?

Answer 14

• Pressure quickly rises above that of atria that are now relaxed (in diastole)
• Increase in pressure causes blood to flow back toward the atria, closing the tricuspid and mitral valves

Question 15

Why do SL valves open and blood is ejected during ventricular ejection (2nd phase of ventricular systole)?

Answer 15

Contraction of ventricular muscle has raised pressure within ventricle to greater than pressures in pulmonary trunk and aorta. Blood pumped from heart, pushing SL valves open.

Question 16

Why is pressure generated by left ventricle be greater than right?

Answer 16

Since the existing pressure in the aorta will be so much higher

Question 17

Despite difference in pressure generated by ventricles, how does volume of blood pumped compare?

Answer 17

Both ventricles pump the same amount of blood. This quantity is referred to as stroke volume. Stroke volume will normally be in the range of 70–80 mL

Question 18

What does ventricular diastolic follow?

Answer 18

Repolarisation of ventricles

Question 19

What represents ventricular diastole on ECG?

Answer 19

T wave

Question 20

What are 2 phases of ventricular diastole?

Answer 20

1. Isovolumic ventricular relaxation phase (1st phase)

2. Late ventricular diastole (2nd phase)

Question 21

What happens during isovolumic ventricular relaxation phase?

Answer 21

Pressure within the ventricles drops below pressure in both the pulmonary trunk and aorta, blood flows back toward the heart, producing the dicrotic notch (small dip) seen in blood pressure tracings

The semilunar valves close to prevent backflow into the heart

Question 22

Why is there no change in volume of blood in ventricle during isovolumic ventricular relaxation phase?

Answer 22

Since the atrioventricular valves remain closed at this point

Question 23

What occurs during late ventricular diastole?

Answer 23

As the ventricular muscle relaxes, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria

Question 24

What happens when ventricle pressure drops below atrial pressure?

Answer 24

Blood flows from atria to ventricles and pushes open AV valves.

Blows from major veins into relaxed atria and from there into ventricles

Both chambers are in diastole, the atrioventricular valves are open, and the semilunar valves remain closed

The cardiac cycle is complete.