Cardiac Cycle

Question 1

The AV node is an elongated structure which propagates an action potential slowly. Why is this important?

Answer 1

To give time fo atrial depolarisation to complete before ventricular depolarisation begins

Question 2

What is the name of the part of the heart conducting system that comes after the AV node but before the bundle branches?

Answer 2

Bundle of His

Question 3

What is the name of the large diameter conducting cells which rapidly distribute the action potential throughout the ventricles of the heart?

Answer 3

Purkinji fibres

Question 4

Contraction of cells at the apex of the heart starts slightly earlier so as go push blood up towards the valves.T/F?

Answer 4

True

Question 5

What is the name for the slow depolarisation at the start of an SA node action potential?

Answer 5

Pacemaker potential

Question 6

At the threshold potential, the influx of which ion at the SA node initiates a depolarisation?

Answer 6

Calcium ions

Question 7

How does repolrisation of the SA node occur?

Answer 7

Outward movement of potassium

Question 8

The influx of which ion in purkinji fibres causes a depolarisation?

Answer 8

Sodium ions

Question 9

Why is there not immediate repolarisation in Purkinji fibres?

Answer 9

Because of L-type calcium ion channels which still allow a calcium influx

Question 10

At what point in the cardiac cycle are all the heart valves closed?

Answer 10

Isovolumetric ventricular contraction

Question 11

Describe the events that occur in systole for ventricular ejection to initiate

Answer 11

The ventricles start to contract at the start of systole, whilst all of the heart valves are closed. This increases the pressure in the ventricles so that it exceeds that of the aorta and pulmonary trunk so that the semilunar valves open and the contraction of the ventricles pushes blood into the arteries

Question 12

Atrial contraction occurs after most of the ventricular filling has taken place. T/F?

Answer 12

True

Question 13

Describe the events of diastole.

Answer 13

As the ventricles relax, ventricular pressure decreases below that of the pressure in the arteries so the semilunar valves close. The atria starts to fill with blood which increases atrial pressure above that of ventricular pressure to open the Av valves so that blood flows into the ventricles. At the end of diastole, the SA node discharges and the atria depolarise - this is the atrial kick and pushes the last volume of blood in the atria into the ventricle.

Question 14

What is the starling mechanism?

Answer 14

This is the law which states that the more blood which fills the heart (the more stretched the heart is) , the harder the heart will work to pump the increased volume of blood out of the heart