Unit 1: CV System Part F

Question 1

What are the 2 stages of the cardiac cycle?

Answer 1

1. Diastole
2. Systole

Question 2

Diastole

Answer 2

period of relaxation and filling

Question 3

Systole

Answer 3

period of contraction and
emptying

Question 4

What does 1 cardiac cycle involve?

Answer 4

involves systole + diastole of the
atria and systole + diastole of the ventricles.

Question 5

Describe what happens during the phase of the cardiac cycle when the heart is at rest and filling

Answer 5

period of both atrial and ventricular diastole

Ø Pressure in ventricles is lower than in atria, so AV valves (tricuspid/ bicuspid) are open and passive ventricular filling occurs
– blood entering relaxed atria passes into the relaxed ventricles under its own pressure

Ø Ventricular volume increases.

Question 6

Describe what happens during the phase of atrial contraction

Answer 6

(atrial systole, end of ventricular diastole)
ØContraction of the atria drives the last ~20% of atrial blood
volume into the ventricles.

ØThe volume of blood now in each ventricle is called the End-diastolic volume (EDV

Question 7

Describe what happens during the phase of isovolumetric contraction of ventricles

Answer 7

(start of ventricular systole)
Ø early ventricular contraction that occurs prior to a change in
ventricular blood volume

Ø ventricular pressure quickly increases causing AV valves to close

ØTurbulent blood flow caused by closure of the AV valves causes first heart sound (“lub”)

Ø but pressure is not yet high enough to causes ejection, so blood is unable to enter or exit the ventricles

ØAt the same time, atria are in diastole and filling

**VOLUME OF BLOOD IN VENTRICLES ISN’T CHANGING **

Question 8

Describe what happens during the phase of Ventricular ejection

Answer 8

(ventricular systole, atrial diastole)

Ø increasing pressure in ventricles forces semilunar valves open

Ø ~ ½ of ventricular blood volume enters aorta from the left
ventricle (and pulmonary arteries via the right ventricle).

Volume of blood left in each ventricle at the end of ejection =
End Systolic Volume

Question 9

Describe what happens during the phase of Isovolumetric relaxation of ventricles

Answer 9

(start of ventricular diastole)
Ø once ventricular pressure declines below aortic pressure, the
semilunar valves close

ØTurbulent blood flow caused by semilunar valve closure results in second heart sound (“dup”)

Ø ventricular tension decreases, and pressure falls, but still too
high for AV valves to open, so no blood enters ventricles

**BLOOD VOLUME REMAINS THE SAME **