2 The heart as a pump & CVS development

Question 1

Describe the properties of cardiac muscle fibres

Answer 1

straited, branching, central nuclei (1/2 per cell), intercalated discs, gap junctions
T tubules in line with Z bands (not A-I bands)
cells contract in response to AP, influx of Ca2+, excitation spread from cell to cell

Question 2

How does the organisation of the ventricular walls facilitate pumping?

Answer 2

ventricular muscles organised into figure of 8 bands, squeezes chambers to eject blood through outflow valve (pulmonary & aortic)
apex contracts first, then relax LAST - to prevent backflow

Question 3

What are the fundamental changes of a cardiac cycle?

Answer 3

pressure flow changes & valve operation

Question 4

Describe a cycle of myocardium contraction

Answer 4

AP generated by SAN regularly & spontaneously (specialised pacemaker cells)
excitation spreads over atria (internodal tract) to AVN (delay 120ms) - atria completely contract
down muscular septum (between 2 ventricles) through bundle of His (then L bundle branch to R) through to apex then purkinje fibres
exxcitation: endocardium –> epicardium UP towards AV junction where tricuspid & mitral valves are

Question 5

Define systole

Answer 5

contraction & ejection of blood (from ventricles)

Question 6

Define diastole

Answer 6

relaxation & filling (of ventricles)

Question 7

What are the main differences between the right & left heart?

Answer 7

Right: has pacemaker SAN on RA, much lower pressure (only travel to lungs
Left: thicker myocardium, generate enough force to get blood around entire body

Question 8

What happens when pressure in right heart increases?

Answer 8

pulmonary hypertension

Question 9

Describe the sequence of pressure & volume changes in the left atrium & ventricle over a complete cardiac cycle in the normal individual, including when valves shut and open

Answer 9

atrial systole: high atrial pressure
AV valves open: atrial pressure > ventricular pressure
early diastole: intraventricular pressure falls (ventricles fill)
rapid filling: ventricules fill until intraventricular pressure = atrial pressure (more increase in ventricular pressure closes AV valves)
ventricles contract: isovolumerically at first (ventricles contract with no change in volume, both set of valves closed), intraventricular pressure rise until > diastolic pressure in arteries (aortic & pulmonary valves open)
arterial pressure > IV pressure, outflow valves shut

Question 10

Describe when in the cardiac cycle each valve in the heart opens & closes, and the pattern of flow through each valve

Answer 10

AV valves open when atrial pressure > ventricular pressure
AV valves shut when IV pressure > atrial pressure (prevent backflow)
outflow valves open when IV pressure > diastolic pressure of arteries
outflow valves shut when diastolic pressure of arteries > IV pressure

Question 11

Explain the origin of the 1st & 2nd heart sounds

Answer 11

1st heart sound: when the AV valves close ‘lub’

2nd heart sound: when the semilunar valves close (outflow) ‘dub’

Question 12

When does the 3rd & 4th heart sound appear?

Answer 12

3rd: ventricular filling (early diastole) - normal in children, pathology in adults
4th: atrial contraction

Question 13

What do murmurs at rest show?

Answer 13

disturbed flow e.g. through stenosed valve (narrowed) or backflow in faulty valve

Question 14

What are cusps of mitral & tricuspid valves attached to? What are their functions?

Answer 14

papillary muscles via chordae tendinae (fibrous strings attached to valves to papillary muscles) - prevents inversion of valves on systole

Question 15

Describe the structure of the heart, naming the chambers, valves, & main vessels

Answer 15

right: superior & inferior vena cava (from body) enters RA, through tricuspid valves into RV out through pulmonary valve into pulmonary artery to lungs
left: pulmonary vein into LA pass mitral valves into LV out through aortic valves into aorta to rest of body