4.18d Preload

Question 1

What two main factors influence cardiac contractility?

Answer 1

Preload and afterload.

Question 2

What is preload?

Answer 2

How much the ventricles fill with blood; the end-diastolic volume.

Question 3

What is afterload?

Answer 3

The resistance the ventricles must overcome to eject blood.

Question 4

According to the Frank-Starling mechanism, what happens when end-diastolic volume increases?

Answer 4

The heart contracts harder, increasing stroke volume.

Question 5

How does the balloon analogy explain preload?

Answer 5

The more you stretch a balloon, the stronger it recoils; similarly, the ventricle contracts harder when stretched more.

Question 6

How does ventricular elasticity affect stroke volume?

Answer 6

More stretch increases recoil force, pushing out more blood.

Question 7

What additional factor (beyond elasticity) makes the heart different from a balloon?

Answer 7

Cardiac muscle contains actin and myosin filaments.

Question 8

How does actin-myosin overlap influence contractility?

Answer 8

Too little or too much overlap reduces force; optimal overlap maximizes force.

Question 9

What happens to actin-myosin overlap as preload increases?

Answer 9

It moves toward the optimal overlap, increasing contractile force.

Question 10

How does optimal actin-myosin overlap affect stroke volume?

Answer 10

It maximizes contractile force, increasing stroke volume.

Question 11

What is the overall effect of greater end-diastolic volume on the heart?

Answer 11

It increases force of contraction and stroke volume.