Cardiac Cycle

Question 1

How long does an action potential last?

Answer 1

280ms. It is a single contraction.

Question 2

How do pacemakers work?

Answer 2

They generate one action potential at regular intervals.

Question 3

What are the two phases of the cardiac cycle?

Answer 3

Systole (each action potential) and diastole (the intervals between the action potentials)

Question 4

Where is the natural pacemaker?

Answer 4

At the sino atrial node in the wall of the right atrium.

Question 5

What is the delay of the excitement at the atrio ventricular node?

Answer 5

Around 120ms.

Question 6

Describe the events that lead to ventricle contraction.

Answer 6

Signal received by the atrio ventricular node, this spreads the signal down the septum (between the ventricles).
This then spreads through the ventricular myocardium from inner to outer surface. (Endocardial to epicardial).
The ventricle then contracts from the apex up to force the blood up towards the outflow valves.

Question 7

How frequent does the sino atrial node generate an action potential at rest?

Answer 7

Once a second. This increases during activity.

Question 8

How long is ventricular systole?

Extra point - is atrial systole longer or shorter?

Answer 8

Ventricular systole is 280ms.

Extra point - atrial systole is shorter.

Question 9

How long is relaxation in the heart?

Answer 9

700ms.

Question 10

What fills the ventricles?

Answer 10

The veins during diastole.

Question 11

Where do the ventricles pump blood during systole?

Answer 11

Into the arteries for it to go around the whole body. (Or to the lungs if pulmonary artery)

Question 12

What causes the mitral valve to open and close?

Answer 12

It is open when the atrial pressure is higher than the ventricular pressure.
It is closed when the ventricular pressure is higher than the atrial pressure.

Question 13

What causes the aortic valve to open and close?

Answer 13

It is open when the intraventricular pressure is higher than the aortic pressure.
It is closed when the aortic pressure is higher than the ventricular pressure.

Question 14

Starting towards the end if ventricular systole, what is happening at this stage of the cardiac cycle?

Answer 14

The ventricles are contracted with a high intraventricular pressure. Blood is flowing through the outflow valves.

Question 15

What happens in the cardiac cycle when the ventricles begin to relax?

Answer 15

The intraventricular pressure falls and becomes less than the arterial pressure making the outflow valves close.
Isovolumetric relaxation occurs.

Question 16

What happens in the cardiac cycle during diastole?

Answer 16

The atrial pressure is higher than the atrial pressure so blood drains into it.

Question 17

What happens in the cardiac cycle at the beginning of diastole.

Answer 17

The atrioventricular valves open and blood flows to the ventricles because the ventricular pressure is lower than the atrial pressure.
this is called the rapid filling phase and lasts 200-300ms.

Question 18

What happens in the cardiac cycle during diastole.

Answer 18

The ventricles fill more slowly as the ventricular pressure matches the atrial pressure. Then filling stops.

Question 19

What happens in the cardiac cycle during atrial systole?

Answer 19

A small amount of extra blood is pumped into the ventricles.

Question 20

What happens in the cardiac cycle during ventricular systole?

Answer 20

Te ventricular pressure rises rapidly and exceeds the atrial pressure. All valves close.
isovolumetric contraction

Question 21

What is the rapid ejection phase?

Answer 21

When the outflow valves open and blood flows into the arteries.

Question 22

What happens in the cardiac cycle towards the end of systole?

Answer 22

The rate of blood flow falls. Atrial and ventricular pressure peaks and the outflow ceases. (There is still some blood in the ventricle)

Question 23

What are the 2 main sounds associated with the valves closing?

Answer 23

Lup - closure of the atrioventricular valves.

Dup - closure of the outflow valves.

Question 24

At which stage in the cardiac cycle would you hear a lup sound?

Answer 24

At onset of the ventricular systole.

Question 25

At which stage in the cardiac cycle would you hear a dup sound?

Answer 25

At the end if ventricular systole.

Question 26

How long is the interval between the lup and dup sounds?

Answer 26

At rest it is 280ms between the first and second.

The interval from the second back to the first is 700ms.