The Cardiac Cycle

Question 1

How does blood flow into the ventricles?

Answer 1

1. There is a higher blood pressure in the atria as the atria are contracting
2. There is a lower blood pressure in the ventricles because the ventricles are relaxing and emptying of blood
3. So blood flows from the atria into the ventricles down a pressure gradient pushing open the AV valves

Question 2

How do the atrioventricular valves close?

Answer 2

1. There is a higher pressure in the ventricles because the ventricles are contracting and filling
2. There is a lower pressure in the atrium because the atrium are relaxing and emptying
3. So blood flows from the ventricles to the atrium down a pressure gradient
4. Forcing the atrioventricular valves to close

Question 3

How does blood flow out of the heart?

Answer 3

1. There is a higher pressure in the ventricles due to the ventricles contracting and filling
2. There is a lower pressure in the arteries due to the arteries emptying of blood
3. So the blood flows from the ventricles up to the arteries down a pressure gradient
4. Forcing the semi-lunar valves to open

Question 4

How do semi-lunar valves close?

Answer 4

1. There is a higher pressure in the arteries because the arteries are filling with blood
2. There is a lower pressure in the ventricles as the ventricles are relaxing and emptying of blood
3. Blood flows from the arteries back down into the ventricle down a pressure gradient
4. Forcing the semi-lunar valves closed

Question 5

What is the equation for calculating cardiac output?

Answer 5

Stroke volume x heart rate