Session 2

Question 0

Describe in general terms the properties of cardiac muscle which allow the heart to operate as a pump

Answer 0

Striations, branching, centrally positioned nuclei, intercalated discs, Adherens type junctions, gap junctions, T tubules in line with Z bands.
Pacemaker cells.

Question 1

Describe the basic structure of the heart, naming the chambers, valves and main vessels

Answer 1

Superior/inferior vena cava –> right atrium –> tricuspid valve –> right ventricle –> pulmonary valve –> pulmonary artery
Pulmonary vein –> left atrium –> mitral valve –> left ventricle –> aortic valve –> aorta

Question 2

Define the terms ‘systole’ and ‘diastole’

Answer 2

Systole - period when the myocardium is contracting (280 ms)

Diastole - relaxation in between contractions (700 ms)

Question 3

Describe how the organisation of the muscle in ventricular walls facilitates the pumping of blood

Answer 3

Myocardium is organised into figure of 8 bands that squeeze the ventricular chambers forcefully in a way most effective for ejection. The apex of the heart contracts first and relaxes last to prevent back flow.

Question 4

Describe the main differences between right and left heart

Answer 4

Right heart - pumps deoxygenated blood to the lungs, has the pacemaker (SAnode)
Left heart - pumps oxygenated heart to the rest of the body, thicker myocardium

Question 5

Describe the sequence of pressure and volume changes in the atria and ventricles over a complete cardiac cycle in the normal individual

Answer 5

In early diastole ventricular mass relaxes so interventricular pressure falls below atrial pressure. When pressure in LA>pressure in LV, the inflow valves open and blood is forced rapidly into the ventricles (rapid filling phase)
Filing of the ventricles continues through diastole until intraventriuclar pressure matches atrial pressure.
Atrial systole is contraction of the atria, forcing a small amount of blood into ventricles.
After a short delay, the ventricles begin to contract, causing intraventriuclar pressure to rise above atrial pressure. A little blood flows back through the mitral valve causing turbulence which causes the valve to close forcibly.
The ventricles contract isovolumetrically and intraventricular pressure increases until it exceeds the diastolic pressure in the atria and the outflow valves open (rapid ejection period).
Towards the end of systole, intraventricular pressure falls, and when it is below atrial pressure the outflow valves close due to back flow of blood.

Question 6

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

Answer 6

Early diastole - mitral/tricuspid valves open
Early systole - mitral/tricuspid valves close
Start of systole - aortic/pulmonary valves open
End of systole - aortic/pulmonary valves close

Question 7

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

Answer 7

1st heart sound - AV valves close, lup

2nd heart sound - semi lunar valves close, dub

Question 8

Define the terms ‘cardiac output’, ‘stroke volume’ and ‘heart rate’

Answer 8

Cardiac output - volume pumped per minute by the left heart
Stroke volume - volume ejected per cardiac cycle
Heart rate - number of cycles per minute