Session 2

Question 0

Where are the pacemaker cells located in the heart?

Answer 0

In the sino atrial node.

Question 1

Describe myocardium

Answer 1

Consists of individual cells joined by low electrical resistance connections. Contraction of each cell is produced by a rise in intracellular calcium concentration triggered by an all or none electrical event in the cell membrane.

Question 2

How does an action potential spread through the heart?

Answer 2

Excitation spreads over the atria to the AVN. It is then propagated down the septum between the ventricles to excite the ventricular muscle from the endocardial side. From here the contraction spreads through the ventricular myocardium and towards the AV junction where the valves are located

Question 3

Describe ventricular systole

Answer 3

Due to the structure of the ventricular muscle (figure of eight bands) the ventricular chamber forcefully contracts for maximal ejection through the out flow valve

Question 4

What is the rapid filling phase?

Answer 4

The phase when the ventricles fill following distension of the atria.

Question 5

Describe the pressure changes ventricular systole

Answer 5

Intra-ventricular pressure rises, blood flows the ‘wrong’ way through AV valves, closing them. Ventricles then contract isovolumetrically and intraventricular pressure rises until it exceeds diastolic pressure. Outflow valves open and there’s a period of rapid ejection of blood. Both intraventricular and arterial pressure rise to a maximum.

Question 6

What does the first heart sound sound like?

What causes this?

Answer 6

‘lup’ - caused by the AV valves closing, causing oscillations in other structures including the column of blood in the arteries. Crescendo-descendo quality

Question 7

What does the second heart sound sound like?

What causes this?

Answer 7

‘dup’ - caused by semi-lunar valves closing, inducing oscillations in other structures. Has a shorter duration, higher frequency and lower intensity than the first sound.

Question 8

What is a murmur?

Answer 8

Heart sound produced by turbulent blood flow e.g. through a narrowed valve or back flow through an incompetent valve

Question 9

How is cardiac output measured?

Answer 9

Volume pumped per minute by the left heart. Product of stroke volume and heart rate.

Question 10

Outline the basics of circulation

Answer 10

Heart –> resistance vessels –> exchange vessels –> capacitance vessels –> heart.

Question 11

How long does systole last?

Answer 11

280ms

Question 12

How long does ventricular relaxation last?

Answer 12

700ms

Question 13

How long does the rapid filling phase last?

Answer 13

200-300ms

Question 14

Define stenosis

Answer 14

Narrowing of valves

Question 15

Define incompetence

Answer 15

Valve not closing properly