Section 48.3.2 (Exam 4) Cardiac Cycle

Question 1

What is the cardiac cycle?

Answer 1

both sides contract at the same time—first the two atria, then the two ventricles

Question 2

Why do the atria contract before the ventricles?

Answer 2

When the atria contract, the blood moves into the ventricles

If both contracted simultaneously, the blood would not flow into the ventricles as easily as it does

Question 3

Describe the two phases of the cardiac cycle.

Answer 3

Systole—when ventricles contract

Diastole—when ventricles relax

Question 4

Describe the first heart sound or “lub” sound during the cardiac cycle.

Answer 4

It marks the beginning of systole (ventricular contraction)

The contraction causes the AV valves to close, which creates the sound, and the increasing pressure as the ventricles contract eventually trigger the pulmonary and aortic valves to open

Question 5

As blood is pumped out of the ventricles into the aorta and pulmonary artery, the second heart noise or “dup” sound is made. Describe what causes this sound.

Answer 5

The relaxation of the ventricles as blood is pumped out creates a loss of pressure

Since the pressure is lowered in the ventricles, the semilunar/aortic and pulmonary valves close, creating the sound

Question 6

What are the sounds of the cardiac cycle heard through a stethoscope caused by?

Answer 6

the heart valves slamming shut due to changes in pressure

Question 7

What can defective valves that do not close properly lead to?

Answer 7

A sound called heart murmurs

Question 8

What could happen if the AV valve closes incorrectly?

Answer 8

Backflow of blood, possibly leading to many serious heart conditions