Session 2 - Cardiac cycle & heart as a pump

Question 1

Define the term systole.

Answer 1

contraction & ejection of blood from ventricles

Question 2

Define the the term diastole.

Answer 2

relaxation & filling of ventricle

Question 3

Why does the LV have a thicker wall than the RV?

Answer 3

blood travels at higher pressure

Question 4

Which type of circulation occurs at the right side of the heart? Is this lower or higher pressure?

Answer 4

Pulmonary circulation, lower pressure

Question 5

Which type of circulation occurs at the left side of the heart? Is this lower or higher pressure?

Answer 5

Systemic circulation, higher pressure

Question 6

Describe the flow of blood in the right side of the heart

Answer 6

• Superior & inferior vena cava deliver deoxygenated blood to RA
• Tricuspid valve pumps blood from RA to RV
• Pulmonary valve pumps blood from RV to pulmonary artery to be oxygenated at the lungs

Question 7

Describe the flow of blood in the left side of the heart

Answer 7

• Oxygenated blood from lungs is carried by pulmonary veins to LA
• Mitral valve pumps blood from LA to LV
• Aortic valve carries blood from LV to aorta

Question 8

Explain the origin of the S1 heart sound. Describe what it sounds like.

Answer 8

Originates from closure of mitral & tricuspid valve as ventricular pressure > atrial pressure at beginning of systole (point A)

Lower-pitched, duller, longer

Question 9

Explain the origin of the S2 heart sound. Describe what it sounds like.

Answer 9

Originates from closure of aortic (A2) & pulmonary (P2) valves

Shorter, higher frequency, lower intensity

Question 10

What is aortic valve stenosis?

Answer 10

Valve doesn’t open enough => obstruction to blood flow when valve normally opens

Question 11

What are the 3 causes of aortic valve stenosis?

Answer 11

• Build up of calcium on aortic valve
• Congenital defect (bicuspid form of valve)
• Chronic rheumatic fever – inflammation – commissural fusion

Question 12

What can aortic valve stenosis lead to?

Answer 12

• LS heart failure => syncope & angina
• Increased LV pressure => LV hypertrophy => heart is doing more work
• Microangiopathic haemolytic anaemia => shear stress of RBCs passing through narrowed valves damages them -> removed from the blood by macrophages -> anaemia

Question 13

What are 4 causes of mitral valve regurgitation?

Answer 13

• Damage to chordae tendinea & papillary muscles which prevent prolapse in systole
• Damage to papillary muscles after MI
• LS heart failure leads to LV dilation (enlargement) which can stretch valve
• Rheumatic fever = lead to leaflet fibrosis => disrupt seal formation

Question 14

What is the main cause of mitral valve stenosis?

Answer 14

rheumatic fever

Question 15

How does mitral valve stenosis lead to atrial fibrillation & oesophagus compression?

Answer 15

causes increased LA pressure which leads to increased LA dilation

Question 16

What are the 2 causes of aortic valve regurgitation?

Answer 16

• Aortic root dilation -> leaflets pulled apart
• Valvular damage eg due to endocarditis rheumatic fever

Question 17

What is cardiac output and how is it calculated?

Answer 17

Cardiac output (CO) = volume of blood pumped per minute
CO = Stroke Vol (SV) x Heart Rate (HR)

Question 18

What is preload?

Answer 18

amount ventricles are filled thus stretched in diastole

• Central venous pressure – pressure in large veins draining into heart – higher pressure => heart will fill more & EDV will be greater & EDP will be greater, ventricles will stretch more

Question 19

What is afterload?

Answer 19

the load/resistance/pressure heart must eject blood against
- if pressure in aorta is greater => harder for heart to pump blood
- roughly equivalent to aortic pressure

Question 20

What is contractibility?

Answer 20

the force of contraction for a given fibre length
- increased by stimulation of sympathetic nervous system which increases HR & contractility
-↑ Contractility = greater force of contraction = ↑ stroke volume

• ↓ Contractibility = reduced sympathetic stimulation

Question 21

Explain the Frank-Starling Law of the heart

Answer 21

The more the heart fills (the more ventricles stretch) the harder it contracts (up to a limit)
- Harder the heart contracts = greater the stroke volume
- So in other words = greater EDV = greater contractibility

Question 22

How does aortic stenosis lead to left-side heart failure?

Answer 22

• Decreased outflow from LV to aorta due to stenosed aortic valve
• Causes LV to generate excess pressure to drive blood into aorta
• Leads to LV hypertrophy
• Leads to heart failure as harder for heart to pump blood effectively

Question 23

What are the extrinsic controls of cardiac output

Answer 23

• the contractility can be affected by neurotransmitters, hormones, or drugs acting on the myocardium.
• Noradrenaline & adrenaline increase contractibility
• Increases in sympathetic activity will increase stroke volume at given preload & afterload

Question 24

What are the intrinsic controls of cardiac output?

Answer 24

• rises in venous pressure lead to increased stroke volume
• falls in total peripheral resistance lead to increased stroke volume