Chapter 20 - The Heart - REVIEW

Question 1

Define automaticity

Answer 1

automaticity (autorhythmicity) is the ability of cardiac muscle to contract without neural or hormonal stimulation

Question 2

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

Answer 2

The sinoatrial (SA) node

Question 3

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

Answer 3

the heart would still continue to beat, but at a slower rate. The AV node would act as the pacemaker instead

Question 4

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

Answer 4

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

Question 5

the great cardiac vein drains blood from the heart muscle to the…

Answer 5

right atrium

Question 6

the autonomic centers for cardiac function are located in….

Answer 6

the cardiac centers of the medulla oblongata

Question 7

the serous membrane covering the outer surface of the heart is called the….

Answer 7

visceral pericardium

Question 8

the simple squamous epithelium covering the walls of the heart constitutes the…..

Answer 8

endocardium

Question 9

the heart lies in the……

Answer 9

mediastinum

Question 10

Name 2 functions of the cardiac skeleton of the heart

Answer 10

-physically isolates the muscle fibers of the atria from those of the ventricles

-maintains the normal shape of the heart

Question 11

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

Answer 11

During ventricular contraction, the tension in the papillary muscles pulls on the chordae tendineae, which keeps the cusps of the AV valves from swinging into the atria. This action prevents backflow or regurgitation of blood into the atrium as the ventricle contracts

Question 12

Describe the 3 distinct layers that make up the heart wall

Answer 12

1. epicardium (visceral pericardium) covers the outer surface of the heart
2. myocardium - muscular wall of the heart which forms the atria and ventricles. Contains cardiac muscle tissue and associated connective tissues, blood vessels, and nerves
3. endocardium - squamous epithelium that covers the inner surfaces of the heart, including the valves

Question 13

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

Answer 13

atrioventricular (AV) valves
-tricuspid valve - prevents backflow into the right atrium
-biscuspid/mitral valve - prevents backflow into the left atrium

semilunar valves
-aortic valve - prevents backflow into the left ventricle
-pulmonary valve - prevents backflow into the right ventricle

Question 14

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

Answer 14

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

Question 15

Which is longer — the refractory period of cardiac muscle or skeletal muscle

Answer 15

the refractory period of CARDIAC MUSCLE is longer

Question 16

if the papillary muscles failed to contract, what would happen?

Answer 16

The AV valves would not close properly

Question 17

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

Answer 17

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

Question 18

provide the technical terms for heart contraction and relaxation

Answer 18

heart contraction - systole
heart relaxation - diastole

Question 19

list the phases of the cardiac cycle

Answer 19

1. atrial systole
2. atrial diastole
3. ventricular systole
4. ventricular diastole

Question 20

is the heart always pumping blood when pressure in the left ventricle is rising? explain

Answer 20

no
when pressure in the left ventricle first rises, the heart is contracting but no blood is leaving the heart
during this initial phase of contraction, both the AV and 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 21

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

Answer 21

this would indicate a larger than normal amount of electrical activity during ventricular depolarization.
The cause could be an enlarged heart because more cardiac muscle is depolarizing and the magnitude of the electrical event would be greater

Question 22

Define cardiac output

Answer 22

HR*SV

the amount of blood pumped out by the left ventricle per minute

Question 23

Explain why drinking large amounts of caffeine would increase the heart rate

Answer 23

caffeine has effects on conducting cells and contractile cells that are similar to those of the NE

caffeine acts directly on the conducting system and the contractile cells of the heart, increasing the rate at which they depolarize

Question 24

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 24

this is part of the parasympathetic division of the autonomic nervous system so this would reduce parasympathetic action potentials to the heart.
The resulting sympathetic dominance would increase the heart rate

Question 25

how does a drug that increases the length of time required for the repolarization of pacemaker cells affect the heart rate

Answer 25

this would decrease the heart rate because the pacemaker cells would generate fewer action potentials per minute

Question 26

why is it a potential problem if the heart beats too rapidly?

Answer 26

a heart that beats too rapidly does not have sufficient time to completely fill between beats. thus, when the heart beats too fast, very little blood leaves the ventricles and enters circulation, so tissues suffer damage from inadequate blood supply

Question 27

what effect would stimulating the acetylcholine receptors of the heart have on cardiac output?

Answer 27

this would slow the heart rate.
this will also lower cardiac output because HR is a factor in the formula for cardiac output

(assuming stroke volume remains the same or less)

Question 28

what effect would an increase in venous return have on the stroke volume?

Answer 28

stroke volume = amt of blood pumped out by the ventricles per beat

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.
the more forceful the contraction, the more blood the heart will eject with each beat (stroke volume)

therefore, increased venous return would increase stroke volume (asssuming all other factors are constant)

Question 29

how would an increase in sympathetic stimulation affect the end-systolic volume?

Answer 29

sympathetic stimulation = faster heart rate

end systolic volume = amt left in ventricles after contraction (systole)

LOWER ESV

Question 30

joe’s end-systolic volume is 40mL and his end diastolic volume is 125mL.
what is his stroke volume?

Answer 30

SV=EDV-ESV

125-40=85ML

Question 30

joe’s end-systolic volume is 40mL and his end diastolic volume is 125mL.
what is his stroke volume?

Answer 30

SV=EDV-ESV

125-40=85M

Question 31

During diastole, a chamber of the heart is….

Answer 31

relaxing and filling with blood

Question 32

cardiac output is….

Answer 32

the product of heart rate and stroke volume

Question 33

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

Answer 33

stroke volume

Question 34

What is the cardiac cycle?
What phases and events are needed to complete a cardiac cycle?

Answer 34

the cardiac cycle compromises the events in a complete heartbeat including a contraction/relaxation period for both atria and ventricles

the cycle begins with atria systole as the atria contract and push blood into the relaxed ventricles.

As the atria relax (atrial diastole), the ventricles contract (ventricular systole), forcing blood through the semilunar valves and 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 diastole; passive filling occurs

Question 35

what 3 factors regulate stroke volume to ensure that the left and right ventricles pump equal amounts of blood?

Answer 35

1. Preload (the stretch on the heart before it contracts)
2. Contractility (the forcefulness of contraction of involved ventricular muscle fibers)
3. Afterload (the pressure that must be exceeded before blood can be ejected from the ventricles)

Question 36

How do the cells of the conducting system differ from the contractile cells of the heart?

Answer 36

contractile cells do not normally exhibit automaticity

Question 37

What are the sources and significance of the 4 heart sounds?

Answer 37

S1 - closing of AV valves. “LUBB” marks the start of ventricular contraction

S2 - closing of semilunar valves “DUBB”
marks the start of ventricular diastole

S3 and S4 are quiet

S3=blood flow into the atria

S4=atrial contraction

listening to heart sounds = auscultation

Question 38

differentiate between stroke volume and cardiac output

how is cardiac output calculated

Answer 38

stroke volume is the volume of blood ejected by a ventricle in a single contraction.

cardiac output is the amount of blood pumped by the left ventricle in 1 min

CO=HR*SV

Question 39

what factors influence cardiac output

Answer 39

stroke volume and heart rate

Question 40

what effect does sympathetic stimulation have on the heart?

Answer 40

increases the heart rate and force of contractions

Question 41

describe the effects of epinephrine, norepinephrine, glucagon, and thyroid hormones on that contractility of the heart

Answer 41

all these hormones have positive inotropic effects which means they increase the strength and contraction of the heart

Question 42

Vern is suffering from cardiac arrythmias and is brought to the ER. in the ER he begins to exhibit tachycardia and loses consciousness. explain why vern lost consciousness

Answer 42

when cardiac output decreases to a point where not enough blood reaches the brain, loss of consciousness occurs

during tachycardia, there is little time between contractions for the heart to fill with blood again. thus, the heart pumps less blood out

Question 43

harvey has a heart murmur in his left ventricle that produces a loud “gurgling” sound at the beginning of a systole. which valve is probably faulty?

Answer 43

mitral/bicuspid valve is regurgitating.
When an AV valve fails to close properly, blood flowing back into the atrium produces a murmur.

a murmur at the BEGINNING of a systole indicates an AV valve because this period is when the valve has just closed and the blood in the ventricle is under increasing pressure–thus the likelihood of backflow is the greatest

a sound heard at the END of a systole or even the beginning of a diastole would indicate a semilunar valve (in this case aortic)

Question 44

Person 1: heart rate 75bpm, stroke volume 60mL

Person 2: heart rate 90bpm
stroke volume 95mL

Which person has a greater venous return?

Which person has the longer ventricular filling time?

Answer 44

longer filling time = person 1
(lower heart rate)

greater venous return= person 2
(higher cardiac output. Starling’s law of the heart: greater CO=greater venous return)

Question 45

Karen is taking Verapamil, a calcium channel blocker in cardiac muscle cells.

What effect should this medication have on Karen’s stroke volume?

Answer 45

By blocking calcium channels, verapamil will decrease the force of cardiac contraction, which directly lowers Karen’s stroke volume