Cardiac Cycle

Question 1

ABP equation

Answer 1

ABP = SV x HR x TPR

Question 2

Why are there lots of gap junctions in the atria?

Answer 2

So impulses spread rapidly.

Question 3

Explain a cardiac contraction

Answer 3

Pressure will increase in a chamber when the muscle wall around it contracts. Valves will open when there is a pressure gradient across them. Blood will flow down a pressure gradient, when the valves are open, pressures in the neighbouring chambers change together. When the valves are closed, pressures in the neighbouring chamber can be different.

Question 4

Describe ventricular diastole

Answer 4

Rapid filling. A-V valve is open because the atrial pressure is greater than ventricular. The aortic valve is closed because the ventricular pressure is lesser than the aortic. Pulmonary vein pressure is greater than atrial and ventricular. The atrial contraction increases pressure contributes around 5ml of ventricular filling (very little).

Question 5

Describe ventricular systole

Answer 5

Isovolumetric contraction. Ventricular contraction increases ventricular pressure. When the ventricular pressure is greater than atrial pressure the AV valve closed. Aortic valve is closed and opens when the ventricular pressure is greater than the aortic pressure when the ventricle contracts and ejects into aorta.

Question 6

Describe ventricular diastole isovolumetric relaxation and rapid filling

Answer 6

Ventricle relaxes deceasing the pressure and the aortic valve closes. A-V valve are closed as the ventricular pressure is greater than the atrial pressure. When the atrial pressure increases the A-V valves open.

Question 7

How many phases in ventricular diastole?

Answer 7

3

Question 8

How many phases in ventricular systole?

Answer 8

2

Question 9

Stoke volume equation

Answer 9

End diastolic volume - end systolic volume

Question 10

What happens if there is an increase in heart rate?

Answer 10

You need to shorten the rate of the cardiac cycle by stimulating the p wave sooner. The p wave can move a long way to the left before ventricular filling is comprised.

Question 11

Normal pressures (mmHg) in the heart

Answer 11

Pressures are much lower in the right side of the heart than left, nearly half the pressure. 
aorta = 120/80
pulmonary artery = 25/10
left artery = 8
Left ventricle = 120/8
right artery = 4
right ventricle = 25/4

Question 12

Flow equation

Answer 12

pressure / resistance.

Question 13

Why is the left ventricle more muscular?

Answer 13

Because it needs to reach high pressures to pump the blood further.