Chap 20

Question 0

2. What prevents the AV valves from swinging into the arial?

Answer 0

Contraction of the papillary muscles (just before the rest of the ventricular myocardium contracts) pulls on the chordae tendineae, which prevent the AV valves from opening back into the atria.

Question 1

1. Damage to the semilunar valve of the right ventricle would effect blood flow into which vessel?

Answer 1

Damage to the semilunar valve of the right ventricle would effect blood flow to the pulmonary trunk.

Question 2

3. Why is the left ventricle more muscular than the right ventricle?

Answer 2

The left ventricle is more muscular than the right ventricle because the left ventricle must generate enough force to propel blood throughout the body, except the lungs; whereas the right ventricle must generate only enough force to propel blood a few centimeters to the lungs.

Question 3

4. Define automaticity.

Answer 3

Automaticity, or autorhythmicity, is the ability of cardiac muscle tissue to contract without neural or hormonal stimulation.

Question 4

5. Which structure of the heart is known as the cardiac pacemaker or the natural pacemaker?

Answer 4

The sinoatrial (SA) node is knkow as the cardiac pacemaker or the natural pacemaker.

Question 5

6. If the cells of the SA node did not function, how would the heart rate be affected?

Answer 5

If the cells of the sA node did not function, the heart would still continue to beat, but at a slower rate; the AV node would act as the pacemaker.

Question 6

7. Why is it important for impulses from the atria to be delayed at the AV node before they pass into the ventricle?

Answer 6

If the impulses from the atria wre not delayed at the AV node, they would be conducted through the ventricles so quickly by the bundle branches and Purkinje cells that the ventricles would begin contracting immediately, before the atria had finished their contraction. As a result, the ventricles would not be as full of blood as they could be, and the pumping of the heart would not be as efficient, especially during activity.

Question 7

8. Provide the technical terms for heart contractions and heart relaxation.

Answer 7

The technical term for contraction is systole, and the other term for relaxation is diastole.

Question 8

9. List the phases of the cardiac cycle.

Answer 8

The phases of the cardiac cycle are atrial systole, atrial diastole, ventricular systole, and ventricular diastole.

Question 9

10. Is the heart always pumping blood when pressure in the left ventricle is rising? Explain.

Answer 9

No. When pressure in the left ventricle first rises, the heart is contacting but no blood is leaving the heart. During this initial phase of contraction, both the AV valves and the semilunar valves are closed. The increase in pressure is the result of increased tension as the cardiac muscle contracts. When the pressure in the ventricle exceeds the pressure in the aorta, the aortic semilunar valves are forced open, and blood is rapidly ejected from the ventricle.

Question 10

11. What factor could cause an increase in the size of the QRS complex in an electrocardiogram?

Answer 10

One possible cause for an increase in the size of the QRS complex, which indicates a loarger-than-normal amount of electrical activity during ventricular depolarization, is an enlarged heart. Because more cardiac muscle is depolarizing, the magnitude of the electrical event would be greater.

Question 11

12. Define cardiac output.

Answer 11

Caridac output is the amount of blood pumped by the left ventricle in one minute.

Question 12

13. Caffeine has effects on conducting cells and contractile cells that are similar to those of NE. What effect would dringing large amonts of caffeinated drinks have on the heart?

Answer 12

Caffeine acts directly on the conducting system and contractile cells of the heart, increasing the rate at which they depolarize. Drinking large amounts of caffeinated drinks would increase the heart rate.

Question 13

14. If the cardioinhibitory center of the medulla oblongata were damaged, which part of the autonomic nervous system would be affected, and how would the heart be influenced?

Answer 13

Damage to the cardioinhibitory center of the medulla oblongata, which is part of the parasympathetic division of the autonomic nervous system, would reduce parasympathetic action potentials to the heart. The resulting sympathetic dominance would increase the heart rate.

Question 14

15. How does a drug that increases the length of time required for the repolarizaion of pacemaker cells affect the heart rate?

Answer 14

A drug that increases the length of time required for the repolarizaion of pacemaker cells would decrease the heart rate, because the pacemaker cells would generate fewer action potentials per minute.

Question 15

16. Why is it a potential problem if the heart beats too rapidly?

Answer 15

The heart pumps in proportion to the amount of blood that enters. A heart that beats too rapidly does not have sufficient time to fill completely between beats. Thus, when the heart beats too fast, very little blood leaves the ventricles and enters the circulation, so tissues suffer damage from inadequate blood supply.

Question 16

17. What effect would stimulating the Acetylochoine receptors of the heart valve have on cardiac output?

Answer 16

Stimulating the acetylcholine receptors of the heart would slow the rate. Since cardiac output is the product of stroke volume and heart rate, a reduction in heart rate will lower the cardiac output (assuming that the stoke volume remains the same or doesn’t increase).

Question 17

1. label the diagram

Answer 17

a. superior vena cava
b. auricle of right atrium
c. right ventricle
d. left ventricle
e. aortic arch
f. left pulmonary artery
g. pulmonary trunk
h. auricle of left atrium

Question 18

2. The great cardiac vein drains blood from the heart muscle to the

Answer 18

right atrium

Question 19

3. The autonomic centers for cardiac function are located in

Answer 19

the cardiac centers of the medulla oblongata.

Question 20

4. The serous membrane covering the outer surface of the heart is the

Answer 20

myocardium

Question 21

5. The simple squamous epithelium covering the valves of the heart constitutes the

Answer 21

endocardium

Question 22

6. The heart lies in the

Answer 22

mediastinum

Question 23

7. Identify the structures in the following diagram of a sectional view of the heart.

Answer 23

a. ascending aorta
b. opening of coronary sinus
c. right atrium
d. cusp of right AV (tricupid) valve
e. chordae tendineae
f. right ventricle
g. pulmonary valve
h. left pulmonary veins
i. left atrium
j. aortic valve
k. cusp of left AV (mitral) valve
l. left ventricle
m. interventricular septum

Question 24

8. The cardiac skeleton of the heart has which two of the following functions?

Answer 24

It physically isolates the muscle fibers of the atria from those of the ventricles.
It maintains the normal shape of the heart.

Question 25

9. Cardia output is equal to the

Answer 25

product of heart rate and stroke volume

Question 26

10. During diastole, a chamber of the heart

Answer 26

relaxes and fills with blood

Question 27

11. During the cardiac cycle, the amount of blood ejected from the left ventricle when the semilunar valve opens is the

Answer 27

stroke volume (SV)

Question 28

12. What role do the chordae tendineae and papillary muscles play in the normal function of the AV valves?

Answer 28

During ventricular contraction, tensions in the papillary muscles pulls against the chordeae, which keeps the cusps of the AV valve from swinging into the atrium. This action prevents the backflow swinging into the atrium. This action prevents the backflow, or regurgitation, of blood into the atrium as the ventricle contracts.

Question 29

13. Describe the three distinct layers that make up the heart wall.

Answer 29

1. The epicardium is the visceral pericardium, which covers the outer surface of the heart.
2. The myocardium is the muscular wall of the heart, which forms both atria and ventricles. It contains cardiac muscle tissue and associated connective tissues, blood vessels, and nerves.
3. The endocardium is a squamous epithelium that covers the inner surfaces of the heart, including the valves.

Question 30

14. What are the valves in the heart, and what is the function of each?

Answer 30

The right atrioventricular (AV) valve (the tricuspid valve) and the left AV valve (bicuspid valve) prevent the backflow of blood from the ventricles into the atria. The pulmonary and aortic semilunar valves prevent the backflow of blood from the pulmonary trunk and aorta into the right and left ventricles.

Question 31

15. Trace the normal pathway of an electrical impulse through the conducting system of the heart.

Answer 31

SA node —> AV node —> AV bundle —> right and left bundle branches —> Purkinje fibers (into the mass of ventricular muscle tissue).

Question 32

16. What is the cardiac cycle? What phases and events are necessary to complete a cardiac cycle?

Answer 32

The cardiac cycle comprises the events in a complete heartbeat, including a contraction / relaxation period for both atria and ventricles. The cycle begins with atrial systole as the atria contact and push blood into relaxed ventricles. As the atria relax (atrial diastole), the ventricles contract (ventricular systole), forcing blood through the semilunar valves into the pulmonary trunk and aorta. The ventricles then relax (ventricular diastole). For the rest of the cardiac cycle, both the atria and ventricles are in a diastole; passive filling occurs.

Question 33

17. What three factors regulate stroke volume to ensure that the left and right ventricles pump equal volumes of blood?

Answer 33

The factors that regulate stroke volume are:

1. preload, the stretch on the heart before it contracts;
2. contractility, the forcefulness of contraction of individual ventricular muscle fibers, and
3. afterload, the pressure that must be exceeded before blood can be efected from the ventricles.

Question 34

18. The cells of the conducting system differ from the contractile cells of the heart in that

Answer 34

contractile cells do not normally exhibit automaticity.

Question 35

19. Which of the following is longer?

Answer 35

the refractory period of cardiac muscle

Question 36

20. If the papillary muscles fail to contract,

Answer 36

the AV valves will not close properly.

Question 37

21. Cardiac output cannot increase indefinitely becuase

Answer 37

the available filling time becomes shorter as the heart rate increases.

Question 38

22. Describe the function of the SA node in the cardiac cycle. How does this function differ from that of the AV node?

Answer 38

The SA node, which is composed of cells that exhibit rapid prepotential, is the pacemaker of the heart. The AV node slows teh impulse that signals contraction, because its cells are smaller than those of the conduction pathway.

Question 39

23. What are the sources and significance of the four heart sounds?

Answer 39

The first sound (“lubb”), which marks the start of ventricular contraction, is produced as the AV valves close and the semilunar valves open. The second sound (“dubb” or “dupp”) occurs when the semilunar valves close, marking the start of ventricular diastole. The third heat sound is associated with atrial contraction. Listening to the heart sounds (auscultation) is a simple and effective diagnostic tool.

Question 40

24. Differentiate between stroke volume and cardiac output. How is cardiac output calculated?

Answer 40

Stroke volume (SV) is the volume of blood ejected by a ventricle in a single contraction. Cardiac output (CO) is the amount of blood pumped by the left ventricle in 1 minute: CO (in mL/min) = HR (in beats/min) x SV (in mL/beat).

Question 41

25. What factors influence cardiac output?

Answer 41

Stroke volume and heart rate influence cardiac output.

Question 42

26. What effect does sympathetic stimulation have on the heart? What effect does parasympathetic stimulation have on the heart?

Answer 42

Sympathetic activation increases the heart rate and the force of contractions; parasympathetic stimulation decreases the heart rate and the force of contractions.

Question 43

27. Describe the effects of epinephrine, norepinephrine, glucagon, and thyroid hormones have on the contractility of the heart?

Answer 43

All these hormones have positive inotropic effects, which means that they increase the strength of contraction of the heart.

Question 44

18. What effect would an increase in venous return have on the stroke volume?

Answer 44

The venous return fills the heart with blood, stretching the heart muscle. According to the Frank-Starling principle, the more the heart muscle is stretched, the more forcefully it will contract (to a point). The more forceful the contraction, the more blood the heart will eject with each beat (stroke volume). Therefore, increased venous return would increase the stroke volume (if all other factors are constant).

Question 45

19. How would an increase in sympathetic stimulation of the heart affect the end-systolic volume?

Answer 45

An increase in sympathetic stimulation of the heart would increase heart rate and force of contraction. The end-systolic volume (ESV) is the amount of blood that remains in a ventricle after a contraction (systole). The more forcefully the heat contracts, the more blood it ejects and the lower the ESV is. Therefore, increased sympathetic stimulation should result in a lower ESV.

Question 46

20. Joe’s end-systolic volume is 40 mL, and his end-diastolic volume is 125 mL. What is Joe’s stroke volume?

Answer 46

SV = EDV - ESV, so SV = 125 mL - 40 mL = 85mL.