4. Cardiac Cycle

Question 1

At rest on average how much blood is pumped out of each ventricle per beat? What is this called?

Answer 1

70ml per beat

Stroke volume

Question 2

What causes the cardiac cells to contract?

Answer 2

In response to action potential in membrane

Action potential causes a rise in intracellular calcium

Question 3

How longs the cardiac action potential?

Answer 3

Lasts for duration of single contraction of heart
Around 280ms
Relatively long

Question 4

What are the cusps of mitral and tricuspid valves attached to?

Answer 4

Attach to papillary muscles via chordae tendineae

Prevents inversion of valves on systole

Question 5

Describe the conduction system in the heart

Answer 5

Pacemaker cells in sinoatrial generate an action potential
Activity spreads over atria - atrial systole
Reaches atrioventricular node and delayed for 120ms
From av node excitation spreads down septum between ventricles
Spreads through ventriclar myocardium from inner to outer surface
Ventricle contacts from apex up

Question 6

What are the 7 phases of the cardiac cycle?

Answer 6

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

Question 7

What happens to systole and diastole if heart rate increases?

Answer 7

Systole is always constant

Diastole gets shorter

Question 8

Look at notability for Wiggers diagram for each stage

Answer 8

Now

Question 9

What are the 2 types of abnormal valve function?

Answer 9

Stenosis

Regurgitation

Question 10

What happens in stenosis?

Answer 10

Valve doesn’t open enough

Obstruction to blood flow when valve normally open

Question 11

What happens in regurgitation?

Answer 11

Valve doesn’t close all the way
Back leakage when valve should be closed 
Increase stroke volume 
Systolic pressure increases
Diastolic pressure decreases
Bounding pulse
LV hypertrophy

Question 12

Where are abnormal valve functions usually?

Answer 12

On left side due to high pressure

Question 13

What causes aortic valve stenosis?

Answer 13

Degenerative (senile calcification/fibrosis)
Congential (bicuspid form of valve)
Chronic rheumatic fever - inflammation

Can cause hypertrophy

Question 14

What is microangiopathic haemolytic anaemia?

Answer 14

RBC burst open due to squeezing through a small gap

Question 15

What causes aortic valve regurgitation?

Answer 15

Aortic root dilation (leaflets pulled apart)
Valvular damage (endocarditis rheumatic fever)

Question 16

What happens in mitral valve regurgitation?

Answer 16

Chordae tendineae and papillary muscle normal prevent prolapse in systole
Myxomatous degeneration can weaken tissue leading to prolapse
Blood leaks back into LA and increases preload
Can cause LV hypertrophy

Question 17

What are some other causes of mitral valve regurgitation?

Answer 17

Damage to papillary muscle after heart attack
Left sided heart failure leads to LV dilation which can stretch valve
Rheumatic fencer can lead to leaflet fibrosis which disrupts seal formation

Question 18

What is the main cause of mitral valve stenosis?

Answer 18

Rheumatic fever

Question 19

What happens in mitral valve stenosis?

Answer 19

Commissural fusion of valve leaflets
Harder for blood to flow LA to LV
Increases LA pressure