Regulation Of Cardiac Contraction

Question 1

Length tension relationship: how does the sarcomere look when tension is at its max and min?

Answer 1

Max: sarcomere is relaxed
Min: sarcomere is shortened for a contracted muscle state. OR over stretching of sarcomere causes titin to break, no overlap between thick and thin filament causes there to be no tension (physiologically impossible condition)

Question 2

What is the normal length of sarcomere (resting)

Answer 2

LN- 2.2 micro m

Question 3

What is the optimal length of sarcomere

Answer 3

LO- 2.3 micro m

Question 4

Name the five factors that effect the length tension relationship

Answer 4

1. Overlap of actin and myosin
2. Increased myofilament Ca2+ sensitivity
3. Geometric changes- decreased spacing between myofilaments ( more likely to form crossbridge)
4. Stretch-activated Ca2+ channel activation
5. Increased SR Ca2+ release

Question 5

What do the active and passive length tension curves relate to

Answer 5

Active- contraction of muscle, shortening of sarcomere
Passive- resistance to stretch caused by titin. Sarcomere stiffness

Question 6

Roles of titin

Answer 6

Increase resistance to stretch
Maintain force generation

Question 7

Length tension relationship: does the passive component have more tension in cardiac or skeletal muscle? Explain

Answer 7

More tension in cardiac- can not have any overstretch
Skeletal- has more non-contractile components that can be “turned off” (distensible) allows muscle to be stretched more

Question 8

What are the axis for the frank-starling mechanism graph

Answer 8

Force or stroke volume VS end diastolic volume

Question 9

Define stroke volume

Answer 9

How much blood is pumped out of the heart by the left ventricle

Question 10

What is end diastolic volume

Answer 10

Amount of blood in the heart before contraction

Question 11

Frank-starling (F vs EDV): what kind of tension is provided by systolic and diastolic curves

Answer 11

Systole- active tension
Diastole- passive tension

Question 12

What creates the active tension

Answer 12

Contraction of heart

Question 13

What creates passive tension

Answer 13

Titin. Resistance to filling

Question 14

Frank-starling (F vs EDV): After ejection why does the force not decrease?

Answer 14

Although active tension has dropped, there is an increase in passive tension, thus causing the total force in the heart to remain the same. No descent because of titin and connective tissue

Question 15

With regards to the frank-starling mechanism, where would you label the preload and after load?

Answer 15

Preload= passive tension = diasole
After load= active tension= systole

Question 16

What factors increase EDV

Answer 16

Exercise- more active=sarcomeres stretch, larger chamber
Venous constriction- more blood return, greater volume
Decrease in heart rate- more filling time, amount of blood in chamber increases

Question 17

What things cause passive force in heart

Answer 17

Force of blood on wall and wall on the blood
Titin and non-contractile proteins increasing stiffness

Question 18

What is preload?

Answer 18

Force that stretches the relaxed muscle cells (ex. Blood filling and stretching walls during diastole)
Preload=end diastolic volume

Question 19

What is afterload?

Answer 19

Force against which the contracting muscle must act. Aortic pressure must be overcome to open aortic valve and eject blood.
Afterload=blood pressure

Question 20

Force-velocity curve: why can Vmax not be reached?

Answer 20

To have vmax we much have zero force/load. That would mean having no blood to move which doesn’t occur in living humans

Question 21

What are the axis of the force-velocity curve

Answer 21

Velocity of shortening VS force/load

Question 22

What is the name of the condition when max force is generated

Answer 22

Isometric

Question 23

What happens during isometric contraction

Answer 23

Ventricles contract but the valves are closed so no volume changes occur (isovolumetric). Force is max and velocity of shortening is zero (on force velocity curve)

Question 24

What is an isotonic contraction

Answer 24

Occurs when the heart muscles shorten and the force generated in greater than the load

Question 25

When we decrease the force in the heart, what load are we decreasing?

Answer 25

Preload

Question 26

When we decrease the force in the heart, how does the velocity of shortening change?

Answer 26

Slower velocity, less to push out

Question 27

How do we determine Vmax values experimentally?

Answer 27

Rate of cross bridge cycling