Chapter 9 - Guyton

Question 1

The ventricles then supply the main

pumping force that propels the blood either:

Answer 1

1) through the pulmonary circulation by the right ventricle or 2) through the peripheral circulation by the left ventricle

Question 2

three major types of cardiac muscle:

Answer 2

atrial muscle, ventricular muscle, and specialized excitatory and conductive muscle fibers

Question 3

cell membranes that separate individual cardiac muscle cells from one another

Answer 3

intercalated discs

Question 4

syncytium

Answer 4

cardiac cells are so interconnected that when one
of these cells becomes excited, the action potential spreads to all of them, spreading from cell to cell (atrial and ventricular

Question 5

Resting membrane potential of cardiac muscle is

Answer 5

-85 to -95 mV

Question 6

After the initial spike, the membrane remains depolarized for about 0.2 second, exhibiting a plateau as shown in the figure, followed at the end of the plateau by abrupt repolarization. What is the significance?

Answer 6

The presence of this plateau (0.2-0.3 s) in the action potential causes ventricular contraction to last as much as 15 times as long in cardiac muscle as in skeletal muscle.

Question 7

Why does the plateau in cardiac muscle occur?

Answer 7

prolonged period of depolarization through influx of both sodium and calcium, decreased outflow of potassium prevents return to normal resting level

Question 8

What are the fastest conducting fibers in the heart called?

Answer 8

Purkinje fibers

Question 9

The normal refractory period of the ventricle is ______ second, which is about the duration of the prolonged plateau action potential.

Answer 9

0.25 to 0.30

Question 10

Where does the calcium come from that contributes to the strength of the cardiac muscle contraction?

Answer 10

SR and T-tubules (with only SR calcium the contraction would not be strong enough)

Question 11

What is the significance of mucopolysaccharides?

Answer 11

bind calcium in the T-tubules to keep it available for contractions

Question 12

The strength of contraction of cardiac muscle
depends to a great extent on the concentration of
calcium ions in the:

Answer 12

extracellular fluid

Question 13

Each cycle is initiated by spontaneous generation of an action potential in the:

Answer 13

sinus node

Question 14

P wave

Answer 14

atrial depolarization

Question 15

QRS complex

Answer 15

ventricular depolarization

Question 16

T wave

Answer 16

ventricular repolarization

Question 17

If the atria fail to function, why might the person not notice?

Answer 17

the heart can continue to operate under most conditions even without this extra 20 per cent effectiveness because it normally has the capability of pumping 300-400% more blood than is required by the resting body

Question 18

a wave

Answer 18

atrial contraction (right and left atrial pressure increases)

Question 19

c wave

Answer 19

ventricles begin to contract (increasing pressure in ventricles)

Question 20

v wave

Answer 20

end of ventricular contraction

Question 21

The period of rapid filling lasts for about the first

_____ of diastole.

Answer 21

third

Question 22

What causes the A-V valves to open?

Answer 22

pressure increase in the atria during ventricular systole

Question 23

What is isovolumic contraction of the ventricles?

Answer 23

contraction is occurring in the ventricles but no emptying is occurring because the pressure is not significant enough to push the semilunar valves open

Question 24

During the period of rapid ejection, first third, how much blood is ejected?

Answer 24

70% (remaining 30% during the last two thirds - period of slow ejection)

Question 25

What is the end-diastolic volume?

Answer 25

filling of the ventricles during diastole (110-120mL)

Question 26

What is the stroke volume output?

Answer 26

ventricles empty during systole, volume decreases about 70 mL

Question 27

What is the end-systolic volume?

Answer 27

remaining volume in each ventricle, about 40-50 mL

Question 28

Fraction of the end-diastolic volume that is ejected is called the ejection fraction—usually equal to about ___%.

Answer 28

60

Question 29

Increasing the end-diastolic volume and decreasing the end-systolic volume have what effect on stroke volume?

Answer 29

increases

Question 30

prevent backflow of blood from the ventricles to the atria during systole

Answer 30

A-V valves (mitral and tricuspid)

Question 31

prevent backflow from the aorta and pulmonary arteries into the ventricles during diastole

Answer 31

semilunar valves (aortic and pulmonary artery valves)

Question 32

What is cardiac output?

Answer 32

the amount of blood pumped every minute

Question 33

What are two structural differences between the A-V and semilunar valves?

Answer 33

A-V valves: thin, large diameter so soft closure and slow velocity; semilunar valves: fast closure and high velocity

Question 34

What helps prevent the A-V valves bulging too far backward toward the atria during ventricular contraction?

Answer 34

papillary muscles by the chordae tendineae

Question 35

When listening to the heart with a stethoscope, do you hear the valves opening or closing?

Answer 35

closing

Question 36

first heart sound

Answer 36

closure of A-V valves

Question 37

second heart sound

Answer 37

semilunar valves close at the end of systole

Question 38

Work Output of the Heart

Answer 38

Phase I period of filling, Phase II period of isovolumic contraction, Phase III period of ejection, Phase IV period of isovolumic relaxation

Question 39

preload

Answer 39

degree of tension on the muscle when it begins to contract (end-diastolic pressure)

Question 40

afterload

Answer 40

load against which the muscle exerts its contractile force (aortic pressure)

Question 41

When a person is at rest, the heart pumps only ___

liters of blood each minute.

Answer 41

4-6

Question 42

The basic means by which the volume pumped by the heart is regulated:

Answer 42

1) intrinsic cardiac regulation of pumping in response to changes in volume of blood flowing into the heart and 2) control of heart rate and strength of heart pumping by the autonomic nervous system

Question 43

Within physiologic limits, the heart pumps

all the blood that returns to it by the way of the veins. What mechanism is this?

Answer 43

Frank-Starling mechanism

Question 44

As the ventricles fill in response to _____ atrial
pressures, each ventricular volume and strength of
cardiac muscle contraction increase, causing the
heart to pump increased quantities of blood into the arteries.

Answer 44

higher

Question 45

The cardiac output increases during increased sympathetic stimulation and decreases during increased parasympathetic stimulation. These changes in output caused by nerve stimulation
result both from:

Answer 45

changes in HR and changes in contractile strength of the heart

Question 46

How does excess potassium decrease the strength of heart contraction?

Answer 46

decreases the resting membrane potential in the cardiac muscle fibers (calcium would be opposite)