Heart 7

Question 1

Four factors that determine cardiac output

Answer 1

Heart rate, afterload, preload, and contractility

Question 2

Preload

Answer 2

The muscle load BEFORE contraction is initiated; dependent on ventricular filling

Question 3

Afterload

Answer 3

Muscle load AFTER contraction initiation; determined by arterial pressure

Question 4

What is the difference in muscle tension between preload and afterload?

Answer 4

Preload will generate passive tension on the heart while the ventricles are filling; afterload will be any force within the heart that resists muscle shortening

Question 5

Contractility

Answer 5

The inherent ability of actin and myosin to form cross-bridges and generate contractile force

Question 6

What does contractility have to do with preload and afterload?

Answer 6

Nothing

Question 7

What primarily determines contractility?

Answer 7

Intracellular calcium concentration

Question 8

Contraction

Answer 8

Process by which muscle generates tension or force

Question 9

Two types of muscle contraction

Answer 9

Isometric contraction and isotonic contraction

Question 10

Isometric contraction

Answer 10

Contraction without shortening; usually occurring when the heart can’t generate enough force to meet the afterload

Question 11

Isotonic contraction

Answer 11

Contraction with shortening and constant force; occurs whenever the heart is able to meet the afterload

Question 12

Contraction types during a normal cardiac cycle

Answer 12

Initially the muscle generates isometric contractions until the semilunar valves blow open, in which case they become isotonic contractions

Question 13

Length-Tension relationship of cardiac muscle

Answer 13

Increase in resting cardiac muscle length will increase contraction strength

Question 14

Which cardiac factor is related to the length-tension relationship?

Answer 14

Preload

Question 15

Resting tension

Answer 15

Amount of tension that develops passively by stretching the muscle (i.e., increasing the preload).

Question 16

Graphic view of compliance

Answer 16

Slope of the resting tension curve is determined by this

Question 17

Active tension

Answer 17

Amount of isometric tension that is developed by muscle contraction at a particular muscle length

Question 18

Graphic view of contractility

Answer 18

Slope of the active tension curve on the length-tension graph

Question 19

Compliance

Answer 19

Change in volume in relation to a change in pressure: primary determinant of resting cardiac tension

Question 20

Which type of muscle has a lower compliance: skeletal or cardiac?

Answer 20

Cardiac

Question 21

What is another word for contractility?

Answer 21

Inotropy

Question 22

What would changes in inotropy do to the length-tension graph?

Answer 22

Positive inotropic effect: active curve goes up and to the left
Negative inotropic effect: active curve goes down and to the right

Question 23

How does an increase in preload cause an increase in tension development?

Answer 23

Creates more optimal overlap between thick and thin filaments;
increases calcium sensitivity of myofilaments

Question 24

Changes in preload and their effect on muscle shortening

Answer 24

Increase in preload: more muscle shortening

Decrease in preload: less muscle shortening

Question 25

Changes in afterload and their effect on muscle shortening

Answer 25

Increase in afterload: less muscle shortening

Decrease in afterload: more muscle shortening

Question 26

Increase in contractility achieved by sympathetic nerve stimulation increases what three things?

Answer 26

Amount of muscle shortening, velocity of shortening, and rate of relaxation

Question 27

Force generated by the muscle determines . . .

Answer 27

velocity of shortening.

Question 28

Index of contractility

Answer 28

Maximal velocity of shortening with no load”

Question 29

Maximal isometric force

Answer 29

When the muscle is unable to meet the afterload

Question 30

Increasing preload has what effect on the force-velocity graph?

Answer 30

It has no effect on Vmax, but will increase the velocity of shortening, moving the X-intercept over to the right

Question 31

Increasing contractility has what effect on the force-velocity curve?

Answer 31

Both increases Vmax and the velocity of shortening, increasing both the X- and Y-intercepts