Lecture 21: Cardiac Output

Question 1

Preload

Answer 1

• Extent of ventricular filling
• Workload imposed on the heart before contraction begins
• Also called end-diastolic volume

Question 2

Afterload

Answer 2

The resistance that the ventricles must overcome to empty its content

Question 3

Contractility

Answer 3

• The strength of contraction at any given end-diastolic volume
• Agents that produce an increase in contractility are said to have positive inotropic effects

Question 4

Positive inotropic agents increase

Answer 4

rate and force of contraction

Question 5

Examples of positive inotrophic agents

Answer 5

• Norepinephrine

- Epinephrine

Question 6

Sympathetic stimulation increases stroke volume by

Answer 6

strengthening cardiac contraction and also by enhancing venous return

Question 7

What shifts the Frank-Starling curve to the left

Answer 7

sympathetic stimulation

Question 8

Agents that produce a decrease in contractility are said to have what kind of effects

Answer 8

Negative inotropic effect

Question 9

Negative inotropic agents decrease both

Answer 9

the rate of tension development and the peak tension

Question 10

Example of negative inotropic agent

Answer 10

Propranol

Question 11

Two types of control influence stroke volume

Answer 11

Intrinsic control

Extrinsic control

Question 12

Intrinsic control

Answer 12

The inherent ability of the heart to vary the stroke volume

Question 13

Intrinsic control depends on

Answer 13

the length-tension relationship of cardiac muscle

Question 14

Length tension relationship of skeletal muscle

Answer 14

Resting muscle length is approx. at optimal length (I0) at which maximal tension can be developed during a subsequent contraction

Question 15

When the skeletal muscle is longer or shorter than the optimal length, the subsequent contraction

Answer 15

is weaker

Question 16

For cardiac muscle, the resting cardiac muscle fiber length is _____ than optimal

Answer 16

less

Question 17

An increase in cardiac muscle fiber length

Answer 17

increases the contractile force of the heart on the following systole

Question 18

Main determinant of cardiac muscle fiber length is

Answer 18

the degree of diastolic filling

Question 19

The greater the extent of the diastolic filling,

Answer 19

the larger the end-diastolic volume and the more the heart is stretched

Question 20

The more the heart is stretched,

Answer 20

the longer the initial cardiac fiber length before contraction

Question 21

An increased cardiac muscle fiber length before contraction leads to

Answer 21

a greater force on the subsequent cardiac contraction which leads to a greater stroke volume

Question 22

The intrinsic relationship between the end-diastolic volume and stroke volume is known as

Answer 22

The Frank-Starling Law of the Heart

Question 23

Two factors that extrinsically control the stroke volume

Answer 23

1. Cardiac sympathetic nerves
2. Epinephrine

These factors enhance the contractility of the heart

Question 24

Increased contractility triggered by norepinephrine and epinephrine

Answer 24

• Increased Ca influx
• Extra Ca allows the myocardial fibers to generate more force through greater cross-bridge cycling than they would without sympathetic influence

Question 25

Heart failure

Answer 25

-The inability of cardiac output to keep pace with the demands of the body for supplies and removal of waste

Question 26

Does the parasympathetic system have an effect on ventricular muscle

Answer 26

Nope

Question 27

Affect of parasympathetic system on the atria

Answer 27

negative inotropic effect

Question 28

Mechanism of parasympathetic system on atria

Answer 28

• Acetylcholine increases K+ efflux thus shortening the duration of the action potential leading to decreased ca influx
• Decreases amount of ca entering atrial cells during the action potential, trigger Ca, and the amount Ca released from the SR

Question 29

Parasympathetic system effect on atria is mediated by

Answer 29

muscarinic (M2) receptors