5. The Heart as a Pump

Question 1

Where does the L ventricle lie?

Answer 1

Under sternum and 4th intercostal space on left

Question 2

What are the 2 different types of circulations?

Answer 2

Systemic (L.vent -> aorta)

Pulmonary (R.vent -> pulmonary arteries)

NB. same cardiac output in both circulations

Question 3

Why are the lungs efficiently perfused at a lower pressure than the body?

Answer 3

Pulmonary vascular resistance is much lower than system vascular resistance because the total vascular resistance in the pulmonary vascular bed is much lower than that in systemic circulation.

Question 4

What is the difference between systemic and pulmonary arteries?

Give their mean pressures.

Answer 4

Systemic: moderate size, thick muscular walls, mean: 100mm/Hg

Pulmonary: large diameter, thin elastic walls, mean: 15mm/Hg

Question 5

What is Starling’s Law of the Heart?

Answer 5

Ventricular contractile force increases with increased end diastolic volume.

Thus if more blood delivered to R.vent, it expands to greater diameter, and contracts more strongle.

Question 6

What is preload, and what is it proportional to?

How does an increased preload demonstrate Starling’s Law of the Heart?

What happens to an increased preload in heart failure?

Answer 6

Degree of stretching experienced by the ventricle during diastole. Proportional to end diastolic volume.

An increased preload -> increased end diastolic volume -> increased end-diastolic muscle fibre length -> increased stroke volume and C.O.

Heart failure: ventricles overstretched and weakened, increased preload -> enlarges heart -> weakens it further -> stroke volume decreases

Question 7

Describe the mechanism underlying Starling’s Law of the Heart

Answer 7

A & M filaments have excess overlap at rest, and stretching INCREASES amount of OVERLAP and thus INCREASES CONTRACTION FORCE.

Thus ventricular contractile force increases in proportion to end disatolic volume.

Question 8

How is blood prevented from accumulating in the pulmonary or systemic circulation (due to uneven ventricular output)?

Answer 8

Averaged over several beats, the 2 ventricules eject the same volume of blood = balances the output of the 2 sides of the heart

Question 9

Why is an enlarged heart (detected on an X-ray) a bad sign?

Answer 9

If ventricles enlarged with no corresponding increase in ventricular wall thickness = contracts more weakly than a smaller heart b/c muscle fibres stretched to point where Starling Law does not work anymore, and a LARGE END DIASTOLIC VOLUME produces a SMALLER STROKE VOLUME = heart failure

Question 10

What is the stroke volume for a normal healthy adult male at rest?

Why is the stroke volume not the same as the end-diastolic volume?

What is the EDV ad ESV in a typical heart?

Answer 10

70ml

Always some blood left in the ventricle at end of systole - residual volume

120ml, 50ml

Question 11

What is afterload?

How is compliance connected to afterload?

Answer 11

Flow impedence (resistance) of aorta and large arteries. Depends on diameter and elasticity of tissue.

The HIGHER the compliance, the LOWER the afterload, and the LESS WORK the heart has to do

Question 12

In older people the elasticity of the aorta declines.

a) why is this?
b) what happens to the afterload?
c) how does this affect the stroke volume?

Answer 12

a) elastic tissue progressively lost from the wall and replaced with collagen
b) afterload increases
c) longer period of isovolumetric contraction of the ventricle before aortic valve opens and shorter duration of ejection -> smaller stroke volume -> larger end systolic (residual) volume

an increased afterload decreases C.O.

Question 13

What is ionotropy?

Answer 13

The contractility of the ventricular muscle. Can vary widely (neuronal and hormonal influence)

Question 14

How will an increase in contractility affect residual volume and stroke volume?

What factors increase contractility?

Answer 14

Decreases residual volume and thus increase stroke volume

• Increased blood Ca²⁺
• beta-adrenergic agonists (e.g. adrenaline)
• drugs which stimulate Ca²⁺ entruy into myocardium (e.g. levosimendan)
• cardiac glycosides (e.g. digoxin)
• insulin & glucagon

Question 15

Label A-D

Answer 15

A: pulmonary valve

B: aortic valve

C: mitral valve

D: tricuspid valve

Question 16

Label A-D

Answer 16

A: tricuspid valve

B: mitral valve

C: aortic valve

D: pulmonary valve

Question 17

What keeps the heart valves in position when closed?

What are these structures attached to?

Answer 17

Chordae tendinae - fibrous tedons attached to the valves

Papillary muscles (first part of ventricles to contract in systole)

Question 18

How do papillary muscles work?

Answer 18

Pull on chordae tendineae and pull the valves closed.

Question 19

Label A-H

Answer 19

A: opening of superior vena cava

B: tricuspid valve

C: myocardium of R ventricle

D: papillary muscles

E: mitral valve

F: chordae tendinae

G: interventricular septum

H: myocardium of L ventricle

Question 20

Describe the cardiac cycle

Answer 20

Atrial systole (atriack contraction forces small amount of blood into ventricle) - AS ends, atrial diastole begins -> ventricular systole (phase 1: isovolumetric contraction - vent. contraction pushes AV valves closed but does not create enough pressure to open semilunar valves) (phase 2: vent. pressure increases and exceeds artery = semilunar open and blood ejected) -> ventricular diastole (isovolumetric relaxation - pressure in vent decreases, blood flows back against cusps of semilunar valves and forces them closed, and blood flows into relaxed atria) -> all chambers relaxed, passive ventricular fill

NB: 800ms

Question 21

Why is atrial systole not needed at rest?

Why is it needed during exercise?

Answer 21

The elastic recoil of the ventricular walls as they enlarge during diastole is enough to suck blood into the ventricles without atrial contraction.

Needed during exercise b/c diastole is shortened with the increased heart rate - atria give blood extra push - helps fill expandind ventricles

Question 22

What is AF?

How is it usually detected by the patient?

What would you see on an ECG?

Answer 22

Asynchronous contraction of atria

Dizzy/breathless during exercise

No P waves

Question 23

Label A-F

Answer 23

A: mitral valve closes

B: aortic valve opens

C: aortic valve closes

D: mitral valve opens

E: isovolumetic contraction

F: isovolumetric relaxation

Question 24

What is the first heart S₁ lubb sound?

What is the second heart S2 dupp sound?

Answer 24

AV valve closure followed by opening of semilunar valves

Semilunar valve closure followed by opening of the AV valves

May be 3rd/4th sound (gallops)

Question 25

What is the third heart sound S₃, and what are the implications if heard in adults as opposed to young adults/children?

Where might S₄ be heard?

Answer 25

Heard 1/3 through diastole, coincides with rapid ventricular filling due to turbulent flow in children/young adults. May be heard in adults with heart disease - serious heart damage, poss. valves.

S₄: Immediately before first heart sound due to turbulent flow in ventricle, rare in normal adults.

Amplify with phonocardiogram to investigate.

Question 26

Label A-D, the optimal stethoscope positions for hearing different sounds.

Answer 26

A: aortic semilunar

B: pulmonary semilunar

C: left AV

D: right AV

Question 27

What is the jugular venous pulse?

What are the 3 peaks in a the JVP due to?

Answer 27

No valves between vena cava and R atrium, or pulmonary veins and L atrim, so when R. atrium contracts, a backpressure occurs in the jugular vein, can be felt as faint pulse.

a: atrial contraction just before tricuspid valve closes
c: pressure increasing in atrium just after the tricuspid closes b/c valve bulges back into the atrium
v: ventricles filling when tricuspid valve is closed. (venous pressure increases in people with heart failure)

Question 28

Label what A-C show

Answer 28

A: a wave - atrial contraction before tricuspid valve closes

B: c wave - pressure rising in atrium just after tricuspid closes b/c valve bulges back into atrium

C: v wave - venous filling when tricuspid valve is closed

Question 29

What three main factors mediate venous return to the heart?

Answer 29

1. one way valves in the veins
2. muscular pumps
3. thoraco-abdominal pump (during inspiration, pressures in thoracic cavity are reduced, pulling blood back into inferior vena cava. On exhalation thoracic pressures increase and this blood is forced into the R. atrium b/c/ veins squeezed).