Session 2: Cardiac Cycle

Question 1

At rest, which part of the body does most of the cardiac output supply?

Answer 1

Gut

Question 2

What are resistance vessels?

Answer 2

Arterioles that restrict blood flow to areas of the body that are hard to perfuse

Question 3

What are capacitance vessels?

Answer 3

Veins - enable system to vary amount of blood pumped around the body

Question 4

What is systole?

Answer 4

Period when the myocardium is contracting

Question 5

What is diastole?

Answer 5

Period of relaxation between contractions (ventricles relax and fill with blood)

Question 6

What is stroke volume?

What is the approximate value for this?

Answer 6

Volume of blood pumped by each ventricle per beat at rest ~70ml/beat

Question 7

How much blood is pumped per minute at 70bpm?

What does this value correspond to?

Answer 7

5L/min ~ volume of blood in the body

Question 8

What does the myocardium consist of?

Answer 8

Individual specialised muscle cells joined by low electrical resistance connections (gap junctions)

Question 9

How is contraction of each cell produced?

Answer 9

Rise in intracellular Ca2+ concentration triggered by action potential (an all or none electrical event in the cell membrane)

Question 10

What is the cardiac cycle?

Answer 10

Sequence of pressure flow changes and valve operation that occur with each heartbeat

Question 11

Describe how excitation spreads throughout the different parts of the heart.

Answer 11

• action potential is generated spontaneously at the SA node (pacemaker cells) in the right atrium
• excitation spreads over the atria to the AV node
• it then moves down the muscular septum to excite the ventricular muscle from the endocardial side
• contraction then spreads through the ventricular myocardium and up towards the AV junction - valves located here

Question 12

Complete the sentence: Heart valves open or close depending on _______________________.

Answer 12

Differential blood pressure on either side of the valve.

Question 13

What do the cusps of mitral and tricuspid valves attach to?

Answer 13

Papillary muscles via chordae tendineae

Question 14

What is the function of chordae tendineae?

Answer 14

Anchor the valve leaflets to prevent them from inverting on systole

Question 15

Name the 7 phases of the cardiac cycle.

Answer 15

1. Atrial contraction
2. Isovolumetric contraction
3. Rapid ejection
4. Reduced ejection
5. Isovolumetric relaxation
6. Rapid filling
7. Reduced filling

Question 16

What does the A wave on the Wiggers Diagram denote?

Answer 16

Atrial pressure rising due to atrial systole

Question 17

What role does atrial contraction play in ventricular filling?

Answer 17

It only accounts for final ~10% of ventricular filling (varies with age and exercise)

Question 18

What is the state of all four valves in phase 1 of the cardiac cycle?

Answer 18

Mitral/Tricuspid: open

Aortic/Pulmonary: closed

Question 19

What happens in phase 2 of the cardiac cycle?

Answer 19

ISOVOLUMETRIC CONTRACTION:

• all valves are closed
• blood volume doesn’t change
• intraventricular pressure > atrial pressure (mitral valve shuts)
• rapid rise in ventricular pressure as ventricle contracts

Question 20

What does the C wave on Wiggers diagram denote?

Answer 20

Closing of mitral valve and slight inversion on atria causes this wave in atrial pressure curve

Question 21

What is the S1 sound?

Answer 21

Closure of mitral and tricuspid valves (‘Lub’ sound)