Part 3: Cardiac cylce

Question 1

How are AV valves tethered?

Answer 1

cordae tendinae attach AV valves to papillary muscles - this prevents excessive bulging

Question 2

How much fluid in pericardial cavity?

Answer 2

5-30ml lubricating fluid

Question 3

What are the mechanical events of the cardiac cycle?

Answer 3

Late diastole
Atrial systole
Isovolumetric contraction
Ventricular ejection
Isovolumetric ventricular relaxation

Question 4

What happens in late diastole?

Answer 4

AV valves are open, ventricles receive blood. Pulmonary and aortic valves are closed

Question 5

What occurs in atrial contraction?

Answer 5

Drives 25-30% more blood into ventricles. Contraction narrows veins but some blood regurgitates back into vessels

Question 6

What happens in isovolumetric contraction of ventricle?

Answer 6

tension increases and AV valves close (1st heart sound). Until pressure exceeds arteries and pulmonary /aortic valves open

Question 7

What happens in ventricular ejection?

Answer 7

Ventricles continue to contract rapidly then more slowly. Muscles loose tension and thus pressure. Valves snap shut (second heart sound)

Question 8

What occurs in isovolumetric ventricular relaxation?

Answer 8

pressure falls below atria and AV valves open letting blood into ventricles. AV valves are pulled downwards in ventricular contraction pulling blood into atria which is ready to flow into ventricles when valves open.

Question 9

Systole begins when?

Answer 9

When the AV valves close and ventricular contraction begins

Question 10

Diastole begins when?

Answer 10

Closure of pulmonary and aortic valves and relaxation of ventricles

Question 11

How does the JVP wave occur?

Answer 11

RA is continuos with internal jugular vein functionally due to no valves. Flucuations in pressure is transmitted backwards from atria to give JVP.

Question 12

What are the wave forms of JVP?

Answer 12

a: increase P during atrial systole and decrease venous return
c: increase atrial P as ventricular systole begins (also augmented by carotid pulse)
x descent: following ventricular stretching
v: increase atrial P before AV valves open
y descent: following opening of valves

Question 13

What proportion of time is systole and diastole?

Answer 13

at HR 75bpm
1/3 systole, 2/3 diastole.
At high HR (eg 200bpm) systole can be slightly longer than diastole (160ms vs 140ms)

Question 14

Which atria contracts first?

Answer 14

RA

Question 15

Which ventricle contracts first?

Answer 15

RV - ejects first and the longest, pulmonary valve closes after aortic

Question 16

What is EF?

Answer 16

% EDV made up of stroke volume. Normally around 60%. Can rise in exercise.