CVS S2 - The heart as a pump

Question 1

How does the organisation of cardiac muscle in the ventricular walls facilitate pumping?

Answer 1

Ventricular muscle is organised into figure of eight bands that squeeze the ventricular chamber forcefully, ejecting blood through the outflow valve

Question 2

What part of the heart contracts first in ventricular systole and what is the purpose of that?

Answer 2

Apex of the heart contacts first and relaxes last to prevent backflow

Question 3

Describe the structure of myocardial cells

Answer 3

• Discrete cells connected electrically via intercalated discs and gap junctions
• Striated, branched, single central nuclei, adherence junctions

Question 4

Define systole

Answer 4

Period when myocardium is contracting

Question 5

Define diastole

Answer 5

Period of relaxation between contractions

Question 6

How long does systole and diastole last for

Answer 6

Systole - 280ms

Diastole - 700ms

Question 7

What is the function of pacemaker cells and where are they found?

Answer 7

• Generate cardiac action potential

- Wall of right atrium

Question 8

What is the difference between the stimulation of cardiac muscle and skeletal muscle?

Answer 8

Cardiac muscle is stimulated by the influx of calcium ions into the cell, causing the release of calcium ions from the sarcoplasmic reticulum to initiate muscle contraction

Skeletal muscles are stimulated by the influx of sodium ions which cause depolarisation of the membrane as an action potential travels down T-tubules, causing the release of calcium ions from the sarcoplasmic reticulum

Question 9

What determines whether the atrioventricular valves are open or closed?

Answer 9

Open when pressure in the atria is greater than the ventricles

Closed when pressure in the ventricles is greater than the aorta

Question 10

What physical process causes valves to close?

Answer 10

Back flow of blood

Question 11

Describe the rapid filling phase of the cardiac cycle

Answer 11

• Atrioventricular valves open so ventricles fill rapidly
• Rate decreases as the pressure in ventricles increases as the ventricle walls stretch and pressure in the atria decreases, resulting in a lesser pressure gradient

Question 12

How is it possible that the heart can have normal function without atrial systole?

Answer 12

Ventricles are 75-80% filled before atrial systole and so contraction of the atria only forces small amount of blood into the ventricles

Question 13

What is isovolumetric contraction?

Answer 13

Contraction causing increase in intra-ventricular pressure but no change in volume as all valves are closed

Question 14

Where does the action potential, generated at the SA node, travel to next?

Answer 14

Spreads over atria causing atrial systole

Question 15

How long is the cardiac action potential delayed at the AV node for?

Answer 15

120ms

Question 16

What structure in the septum enables transmission of the action potential from the AV node to the apex of the heart?

Answer 16

Bundle of His

Question 17

What is the origin of the first heart sound?

Answer 17

Closure of the Atrioventricular valves (mitral and tricuspid)

Question 18

What is the origin of the second heart sound?

Answer 18

Closure of the semi-lunar valves (aortic and pulmonary)

Question 19

What is the CAUSE of the second heart sound?

Answer 19

Oscillations in other structures such as the column of blood in the arteries

Question 20

When may a third heart sound be heard?

Answer 20

Early in diastole

Question 21

When may a fourth heart sound be heard?

Answer 21

Atrial systole

Question 22

Why would a heart murmur be a concern if heard at rest but not if heard during exercise?

Answer 22

• Murmurs during exercise are caused by turbulent flow
• At rest a murmur may be due to disturbed flow caused by problems such as a narrowed valve or back flow of blood through an incompetent valve

Question 23

In what order does the cardiac action potential innervate the layers of the heart tissue in the ventricles?

Answer 23

Endocardial surface first to the epicardial surface through the ventricular myocardium