Cardiovascular Physiology 32

Question 1

What is Ejection Fraction?

Answer 1

The amount or percentage of blood that is pumped or ejected out of the ventricles with each contraction

Question 2

What is ventricular ejection fraction?

Answer 2

The fraction of the end-diastolic ventricular volume that is ejected

Question 3

What is the stroke volume in a normal heart?

Answer 3

70mL

Question 4

What measure of ejection fraction indicates problems with the heart?

Answer 4

Less than 55%

Question 5

What is the difference between the ejection fractions of the left and right ventricle?

Answer 5

They are equal, and pump out the same stroke volume

Question 6

Which ventricle is ejection fraction measured in clinically?

Answer 6

Left ventricular ejection fraction

Question 7

How is a Passive-Length tension diagram obtained?

Answer 7

By holding a piece of resting muscle at several predefined lengths and then measuring the tension at each length

Question 8

How is an active length tension diagram obtained?

Answer 8

By stimulating a muscle at each predefined length and then measuring the increments in tension from its resting of passive value

Question 9

What is the difference between the passive-tension curve in cardiac muscle and skeletal muscle?

Answer 9

The passive tension curve rises at lower sarcomere lengths than in skeletal muscle

Question 10

Why can cardiac muscle be stretched further than skeletal muscle?

Answer 10

Because the non contractile components of cardiac muscle are less distensible than in skeletal muscle

Question 11

What component of muscle is distensible?

Answer 11

Titin

Question 12

What does Titin do in muscle cells?

Answer 12

It is distensible and acts as a spring opposing muscle stretch and restoring force during shortening. Allowing a muscle to stretch without breaking

Question 13

How is tension affected by myofilament overlap in active skeletal muscle?

Answer 13

Increased overlap increases tension

Question 14

Why does the active length tension curve rise sharply in cardiac muscle but not in skeletal muscle?

Answer 14

In cardiac muscle there is an increased sensitivity of calcium of the myofilaments and as we stretch the sarcomere more, the spacing is less between the filaments so the probability of cross bridge cycling increases

Question 15

What does increased crossbridge formation in stretched cardiac myocytes do?

Answer 15

Increases calcium affinity of troponin C and this recruits more cross bridges producing greater force

Question 16

What is the result of an increased preload in cardiac muscle?

Answer 16

This increases the stretching of the sarcomere and at the same time increases the sensitivity to calcium resulting in more cross bridges produced and greater force

Question 17

What leads to an increase in active tension in cardiac muscle cell?

Answer 17

Increases in preload

Question 18

What does an increase in preload lead to in cardiac muscle cells?

Answer 18

An increase of active tension and an increases in the rate of active tension development

Question 19

What are the changes in active tension caused by preload related to in cardiac muscles?

Answer 19

Changes in the number of cross bridges formed which depends on the sarcomere length

Question 20

How do changes in preload affect calcium in cardiac muscle cells?

Answer 20

They alter the sensitivity to troponin C to calcium

Question 21

What does skeletal muscle modulate its force generation with?

Answer 21

Changes in motor nerve activity and motor unit recruitment

Question 22

What does changes in contractility allow the heart to do?

Answer 22

Beat harder or less harder to modulate the force generated by contraction

Question 23

What is contractility?

Answer 23

The intrinsic force with which the heart contracts or the measure of the forcefulness of contraction in any given preload

Question 24

What is another term to describe contractility?

Answer 24

The inotropic state of the heart

Question 25

What is an Ionotrope?

Answer 25

A factor that alters the force of contraction in the heart

Question 26

What is an example of a positive ionotrope agent?

Answer 26

Catecholamines, epinephrine or norepinephrine or exercise

Question 27

What does the addition of a positive ionotrope do?

Answer 27

Increases cardiac performance or stroke volume or cardiac output

Question 28

What do positive inotropic agents do?

Answer 28

Increase contractility

Question 29

What is an example of a negative ionotropic agent?

Answer 29

Heart failure

Question 30

What does the addition of a negative ionotrope do?

Answer 30

Decreases ventricular performance by decreasing contractility

Question 31

What does the ability to produce changes in force during contraction result from?

Answer 31

Incremental changes in binding between filaments of myosin and actin

Question 32

What does the degree of binding of actin and myosin depend on?

Answer 32

The calcium concentrations in a cardiac cell

Question 33

What is the action or response of the sympathetic nervous system driven by?

Answer 33

Precisely timed releases of a catecholamine

Question 34

How do factors that cause an increase in contractility work?

Answer 34

They work by causing an increase in intracellular calcium ions during contraction

Question 35

How do factors that cause an increase contractility work?

Answer 35

By increasing the amount of calcium into a myocyte or maintaining higher calcium levels in the cytosol of cardiac myocytes during an action potential

Question 36

How is decreases contractility acheived?

Answer 36

Primarily by decreasing the influx of calcium into the myocyte or maintaining lower calcium levels in the cytosolic myocytes during an action potential

Question 37

What kind of inotropic effect do catecholamines (epinephrine and norepinephrine) have?

Answer 37

A positive inotropic effect increasing contractility

Question 38

What are the mechanisms that the positive inotropic factors use to increase contractility of the heart?

Answer 38

• Increase calcium influx into the cell increasing calcium induced calcium release
• increase sensitivity of the SR calcium release channel to calcium
• Stimulate SERCA to increase calcium stores for later release in the sarcoplasmic reticulum
• Increase calcium influx into the cell which increases stores into the sarcoplasmic reticulum