L6 The Cardiac Cycle

Question 1

How long does one cycle last?

Answer 1

0.8s

Question 2

What is the effect of damaged papillary muscles?

Answer 2

The chordae tendineae cause the valves herniating. In a heart attack, this can cause damage to papillary muscles, causing them to rupture and ischaemic. This means that there is regurgitation in systole. In complete rupture in a server MI, a patient can die.

Question 3

What causes the ‘Lub’ sound?

Answer 3

The mitral and tricuspid valves closing.

Question 4

What causes the ‘Dub’ sound?

Answer 4

The aortic and pulmonary valves closing.

Question 5

What is isovolumetric contraction? When does it occur?

Answer 5

The ventricles are contracting, causing AV valves to close but the pressure in the ventricles has not yet exceeded that of the arteries. This means that the volume in the ventricles stays the same during contraction. This occurs in the initial stage of contraction.

Question 6

Describe the cardiac cycle.

Answer 6

1. Late diastole, both chambers and relaxed and the ventricles gain blood passively, through gravity.
   
   2. Atrial systole, contract and cause a small amount of blood to be pumped into the ventricles.
   3. Isovolumetric ventricular contraction - The first phase of ventricular contraction pushes AV valves closed but does not create enough pressure to open semi-lunar valves.
   4. As the ventricles contract and the pressures increase, the pressure in the ventricles overtake that of the arteries causing blood to push through the semi-lunar valves
      In ventricular diastole, the pressure in the ventricles decrease and the pressure in the aorta is high, this causes the semi-lunar valves to snap shut. This is isovolumetric relaxation.

Question 7

What is the resting stroke volume?

Answer 7

70ml