CARDIOVASCULAR CHAPTER 17 Flashcards
1
Q
1) The apex of the heart is situated toward the: A) posterior rib cage. B) right shoulder. C) left hip. D) left shoulder.
A
C) left hip.
2
Q
2) The heart is situated in the middle of the thoracic cavity in a region known as the: A) dorsal cavity. B) mediastinum. C) pleural cavity. D) cardiac notch.
A
B) mediastinum.
3
Q
3) What surface groove separates the right and left ventricles? A) interatrial septum B) atrioventricular sulcus C) interventricular septum D) interventricular sulcus
A
D) interventricular sulcus
4
Q
4) Both the left and right atria receive blood from: A) the lungs. B) the ventricles. C) veins. D) arteries.
A
C) veins.
5
Q
5) The pulmonary circuit involves blood flow from the heart to the: A) lungs. B) body. C) liver. D) brain.
A
A) lungs.
6
Q
6) The right side of the heart receives:
A) oxygenated blood from the systemic circuit.
B) deoxygenated blood from the pulmonary circuit.
C) deoxygenated blood from the systemic circuit.
D) oxygenated blood from the pulmonary circuit.
A
C) deoxygenated blood from the systemic circuit.
7
Q
7) What is the most superficial layer of the pericardial sac? A) fibrous pericardium B) parietal pericardium C) visceral pericardium D) epicardium
A
A) fibrous pericardium
8
Q
8) What is found between the visceral pericardium and the parietal pericardium? A) the heart B) pericardial fluid C) fibrous pericardium D) the lungs
A
B) pericardial fluid
9
Q
9) The visceral pericardium is the same as the: A) epicardium. B) fibrous pericardium. C) myocardium. D) endocardium.
A
A) epicardium.
10
Q
10) Coronary circulation involves the delivery of oxygenated blood to the: A) liver. B) heart. C) lungs. D) brain.
A
B) heart.
11
Q
11) The right and left coronary arteries receive blood from the: A) aorta. B) pulmonary trunk. C) superior vena cava. D) coronary sinus.
A
A) aorta.
12
Q
12) Which two arteries arise from the right coronary artery?
A) the right anterior interventricular artery and the left posterior interventricular artery
B) the right anterior interventricular artery and the right circumflex artery
C) the left marginal artery and the right circumflex artery
D) the right marginal artery and the right posterior interventricular artery
A
D) the right marginal artery and the right posterior interventricular artery
13
Q
13) Generally, coronary veins empty into a vessel known as the: A) superior vena cava. B) aorta. C) coronary sinus. D) inferior vena cava.
A
C) coronary sinus.
14
Q
14) The coronary sinus does NOT receive blood from the: A) brachiocephalic vein. B) great cardiac vein. C) middle cardiac vein. D) small cardiac vein.
A
A) brachiocephalic vein.
15
Q
15) What is the function of the valves in the heart?
A) promote contraction of the ventricles
B) prevent backflow of blood through the heart
C) eliminate pressure variances within the heart
D) invert during contraction of the ventricles
A
B) prevent backflow of blood through the heart
16
Q
16) Which of the following does NOT return blood to the right atrium of the heart? A) superior vena cava B) coronary sinus C) inferior vena cava D) pulmonary vein
A
A) superior vena cava
17
Q
17) Which of the following vessels carries oxygenated blood? A) pulmonary vein B) superior vena cava C) pulmonary artery D) pulmonary trunk
A
A) pulmonary vein
18
Q
18) Which vessel supplies the systemic circuit with oxygenated blood? A) pulmonary trunk B) aorta C) superior vena cava D) coronary sinus
A
B) aorta
19
Q
19) Which opening in the interatrial septum of the fetal heart connects the right and left atrium? A) fossa ovalis B) ligamentum arteriosum C) foramen ovale D) ductus arteriosus
A
C) foramen ovale
20
Q
20) What muscles, present in the ventricles, anchor the atrioventricular valves by tendon-like chords called chordae tendineae? A) ligamentum arteriosum B) papillary muscles C) pectinate muscles D) trabeculae carneae
A
B) papillary muscles
21
Q
21) Which valve is situated between the left atrium and left ventricle? A) bicuspid (mitral) valve B) tricuspid valve C) aortic valve D) pulmonary valve
A
A) bicuspid (mitral) valve
22
Q
22) What valve prevents the backflow of blood from the right ventricle into the right atrium? A) tricuspid valve B) pulmonary valve C) bicuspid (mitral) valve D) aortic valve
A
A) tricuspid valve
23
Q
23) Which vessel is guarded by a semilunar valve at its base? A) pulmonary trunk B) coronary sinus C) pulmonary vein D) superior vena cava
A
A) pulmonary trunk
24
Q
24) An insufficient mitral valve (bicuspid valve, or left atrioventricular valve) would allow the backflow of blood into the: A) right atrium. B) left ventricle. C) aorta. D) left atrium.
A
D) left atrium.
25
```
25) Blood in the right ventricle arrived from the:
A) right atrium.
B) bicuspid (mitral) valve.
C) pulmonary trunk.
D) pulmonary valve.
```
A) right atrium.
26
```
26) Where should the left ventricle send blood?
A) left atrium
B) pulmonary trunk
C) aorta
D) coronary sinus
```
C) aorta
27
```
27) What vessel(s) deliver oxygenated blood to the left atrium?
A) pulmonary veins
B) pulmonary trunk
C) pulmonary arteries
D) aorta
```
A) pulmonary veins
28
```
28) What vessel delivers oxygenated blood to systemic capillaries for gas exchange?
A) pulmonary trunk
B) aorta
C) coronary artery
D) circumflex artery
```
B) aorta
29
```
29) Autorhythmicity in the heart is the responsibility of:
A) skeletal muscle cells.
B) cardiac pacemaker cells.
C) contractile cells.
D) smooth muscle cells.
```
B) cardiac pacemaker cells.
30
```
30) What characteristic differentiates cardiac muscle cells from skeletal muscle cells?
A) excitability
B) sarcoplasmic reticulum
C) striations
D) intercalated discs
```
D) intercalated discs
31
```
31) What ion movement changes the membrane potential in a contractile cell from negative to positive during the rapid depolarization phase?
A) influx of sodium ions
B) outflow of potassium ions
C) outflow of calcium ions
D) influx of calcium ions
```
A) influx of sodium ions
32
```
32) The rapid influx of calcium ions into pacemaker cells creates a positive membrane potential inside the cell and is responsible for the:
A) minimum potential phase.
B) repolarization phase.
C) full depolarization phase.
D) slow initial repolarization phase.
```
C) full depolarization phase.
33
```
33) During what phase of the action potential will calcium ions enter the contractile cell as potassium ions exit?
A) rapid depolarization phase
B) initial repolarization phase
C) repolarization phase
D) plateau phase
```
D) plateau phase
34
```
34) A contractile cell with a sustained membrane potential of 0 mV is experiencing the:
A) initial repolarization phase.
B) plateau phase.
C) rapid depolarization phase.
D) repolarization phase.
```
B) plateau phase.
35
35) How do cardiac cells sustain a membrane potential of around 0 mV during the plateau phase?
A) calcium channels remain open
B) increased membrane permeability to potassium ions
C) decrease in the amount of calcium diffusing across the membrane
D) increased membrane permeability to sodium ions
A) calcium channels remain open
36
36) The long length of the cardiac action potential, at 200-300 msec, allows for: A) an opportunity for the heart to fill with blood.
B) a reduction in strength of the heart's contraction.
C) less calcium ions to enter cells.
D) a faster heart rate.
A) an opportunity for the heart to fill with blood.
37
```
37) As a result of the long refractory period in the contractile cell, cardiac muscle can NOT exhibit:
A) oxygen debt.
B) tetany.
C) fatigue.
D) treppe.
```
B) tetany.
38
```
38) What do pacemaker cell action potentials lack?
A) plateau phase
B) depolarization
C) repolarization
D) threshold
```
A) plateau phase
39
```
39) Which of the following is NOT a population of pacemaker cells in the heart?
A) sinoatrial (SA) node
B) papillary muscles
C) atrioventricular (AV) node
D) Purkinje fiber system
```
B) papillary muscles
40
```
40) Which of the following pacemaker cell populations has the fastest intrinsic rate of depolarization at about 60-70 times or more per minute?
A) atrioventricular (AV) node
B) atrioventricular (AV) bundle
C) sinoatrial (SA) node
D) Purkinje fiber system
```
C) sinoatrial (SA) node
41
```
41) What normally serves as the pacemaker of the entire heart?
A) Purkinje fiber system
B) atrioventricular (AV) bundle
C) atrioventricular (AV) node
D) sinoatrial (SA) node
```
D) sinoatrial (SA) node
42
42) Determine the impact if the connection between the sinoatrial (SA) node and the atrioventricular (AV) node becomes blocked.
A) The ventricles will contract more quickly.
B) The ventricles will contract more slowly.
C) The ventricular rhythm will not change.
D) The atria will contract more forcefully.
B) The ventricles will contract more slowly.
43
43) Place the following parts of the cardiac conduction system in the order in which they transmit the action potential.
1. atrioventricular (AV) bundle
2. Purkinje fibers
3. sinoatrial (SA) node
4. right and left bundle branches
5. contractile cells of cardiac muscle tissue
6. atrioventricular (AV) node
A) 3, 1, 6, 4, 2, 5
B) 3, 1, 6, 4, 5, 2
C) 3, 6, 1, 4, 2, 5
D) 3, 6, 4, 1, 2, 5
C) 3, 6, 1, 4, 2, 5
44
```
44) What is NOT part of the cardiac conduction system?
A) atrioventricular (AV) node
B) atrioventricular (AV) bundle
C) atrioventricular (AV) valve
D) sinoatrial sinoatrial (SA) node
```
C) atrioventricular (AV) valve
45
```
45) The right and left atria depolarize and contract following the arrival of the action potential from the:
A) Purkinje fibers.
B) sinoatrial (SA) node.
C) atrioventricular (AV) bundle.
D) atrioventricular (AV) node.
```
B) sinoatrial (SA) node.
46
46) A damaged right bundle branch will prevent the passage of the action potential to the:
A) sinoatrial (SA) node.
B) atrioventricular (AV) bundle.
C) Purkinje fibers in the right ventricle.
D) atrioventricular (AV) node.
C) Purkinje fibers in the right ventricle
47
```
47) The P wave on an electrocardiogram (ECG) represents the depolarization of cells in the:
A) atrioventricular (AV) node.
B) sinoatrial (SA) node.
C) atria.
D) ventricles.
```
C) atria.
48
48) On an electrocardiogram (ECG), atrial repolarization is obscured by the: A) P wave.
B) QRS wave.
C) T wave.
D) S-T segment.
B) QRS wave.
49
```
49) Which wave on the electrocardiogram (ECG) represents ventricular depolarization?
A) P wave
B) QRS wave
C) T wave
D) R-R interval
```
B) QRS wave
50
```
50) A damaged atrioventricular (AV) bundle or atrioventricular (AV) node will primarily affect the length of the:
A) P wave.
B) P-R interval.
C) T wave.
D) Q-T interval.
```
B) P-R interval.
51
```
51) Which part of the electrocardiogram (ECG) would most be affected by abnormally slow depolarization of the ventricles?
A) P wave
B) QRS wave
C) T wave
D) R-T interval
```
B) QRS wave
52
```
52) Which of the following can be used to measure heart rate?
A) R-R interval
B) S-T segment
C) Q-T interval
D) P-R interval
```
A) R-R interval
53
53) What activity is occurring in the heart during the Q-T interval on an electrocardiogram (ECG)?
A) The atrial cells are undergoing action potentials.
B) The ventricular cells are repolarizing.
C) The AV node delay occurs as the action potential spreads from the SA node to the atria to the ventricles.
D) The ventricular cells are undergoing action potentials.
D) The ventricular cells are undergoing action potentials.
54
```
54) Archie has a resting heart rate of 125 beats per minute. Classify his cardiac dysrhythmia.
A) tachycardia
B) asystole
C) bradycardia
D) heart block
```
A) tachycardia
55
55) Predict the position of the valves during the ventricular ejection phase.
A) The AV valves are shut while both semilunar valves are forced open.
B) The AV valves are forced open while both semilunar valves are shut.
C) The AV valves and semilunar valves are shut.
D) The AV valves and semilunar valves are forced open.
A) The AV valves are shut while both semilunar valves are forced open.
56
```
56) As ventricular systole begins, all four heart valves are closed during the:
A) ventricular ejection phase.
B) isovolumetric contraction phase.
C) isovolumetric relaxation phase.
D) ventricular filling phase.
```
B) isovolumetric contraction phase.
57
57) What produces the "lub dub" heart sounds?
A) the contraction of the atria, and then the ventricles
B) the relaxation of the atria, and then the ventricles
C) the sound of blood traveling through the heart
D) the vibrations of the ventricular and blood vessel walls when valves shut
D) the vibrations of the ventricular and blood vessel walls when valves shut
58
```
58) End-diastolic volume (EDV) for each ventricle at the end of atrial systole is normally about:
A) 25 ml.
B) 50 ml.
C) 70 ml.
D) 120 ml.
```
D) 120 ml.
59
```
59) The amount of blood remaining in each ventricle at the end of the ventricular ejection phase is normally about:
A) 30 ml.
B) 50 ml.
C) 70 ml.
D) 120 ml.
```
B) 50 ml.
60
60) When is the S2 heart sound heard? A) ventricular filling
B) isovolumetric contraction phase
C) ventricular ejection phase
D) isovolumetric relaxation phase
D) isovolumetric relaxation phase
61
```
61) How much blood is pumped from each ventricle during the ventricular ejection phase?
A) 50 ml
B) 70 ml
C) 90 ml
D) 120 ml
```
B) 70 ml
62
```
62) During what phase does blood flow from the ventricles into the pulmonary trunk and aorta?
A) isovolumetric contraction phase
B) ventricular ejection phase
C) isovolumetric relaxation phase
D) ventricular filling
```
B) ventricular ejection phase
63
```
63) Which chamber experiences a maximum pressure of around 118 mm Hg during contraction?
A) right atrium
B) right ventricle
C) left atrium
D) left ventricle
```
D) left ventricle
64
```
64) Which wave on the electrocardiogram (ECG) corresponds with the ventricular filling phase of the cardiac cycle?
A) P wave
B) S wave
C) T wave
D) S-T segment
```
A) P wave
65
```
65) What wave on the electrocardiogram (ECG) occurs during the ventricular ejection phase of the cardiac cycle?
A) P wave
B) Q wave
C) R wave
D) T wave
```
D) T wave
66
```
66) Calculate the stroke volume (SV) if end-systolic volume (ESV) is 50 ml and the end- diastolic volume (EDV) in a resting heart is 110 ml.
A) 10 ml
B) 50 ml
C) 60 ml
D) 160 ml
```
C) 60 ml
67
```
67) Which of the following volumes should be the greatest?
A) end-diastolic volume (EDV)
B) cardiac output (CO)
C) end-systolic volume (ESV)
D) stroke volume (SV)
```
B) cardiac output (CO)
68
```
68) Calculate cardiac output if the heart rate is 85 beats/minute, end-diastolic volume (EDV) is 130 ml, and end-systolic volume (ESV) is 60 ml.
A) 5950 ml/min
B) 5100 ml/min
C) 7800 ml/min
D) 16,140 ml/min
```
A) 5950 ml/min
69
```
69) Calculate the cardiac output if the heart rate is 100 beats per minute and the stroke volume is 65 ml.
A) 0.65 ml/min
B) 65 ml/min
C) 650 ml/min
D) 6500 ml/min
```
D) 6500 ml/min
70
70) What two values are needed in order to calculate cardiac output (CO) for a ventricle?
A) heart rate (HR) and end-diastolic volume (EDV)
B) stroke volume (SV) and heart rate (HR)
C) stroke volume (SV) and blood pressure (BP)
D) end-diastolic volume (EDV) and end-systolic volume (ESV)
B) stroke volume (SV) and heart rate (HR)
71
```
71) The volume of blood pumped by each ventricle in one heartbeat is known as:
A) end-diastolic volume (EDV).
B) stroke volume (SV).
C) heart rate (HR).
D) cardiac output (CO).
```
B) stroke volume (SV).
72
```
72) Stroke volume averages about:
A) 25 ml per heartbeat.
B) 70 ml per heartbeat.
C) 120 ml per heartbeat.
D) 180 ml per heartbeat.
```
B) 70 ml per heartbeat.
73
```
73) The degree of stretch experienced by the sarcomeres in the ventricle cells before they contract is called:
A) afterload.
B) contractility.
C) stroke volume.
D) preload.
```
D) preload.
74
```
74) What largely determines preload?
A) stroke volume
B) end-diastolic volume (EDV)
C) end-systolic volume (ESV)
D) afterload
```
B) end-diastolic volume (EDV)
75
75) What best describes the Frank-Starling law?
A) The Frank-Starling law states that the greater the volume of blood discharged from the heart, the greater the pressure required to discharge the blood.
B) The Frank-Starling law states that the slower the heart rate, the greater the cardiac output.
C) The Frank-Starling law states that the greater the stroke volume, the greater the heart rate.
D) The Frank-Starling law states that the more the ventricular muscle cells are stretched, the more forcefully they contract.
D) The Frank-Starling law states that the more the ventricular muscle cells are stretched, the more forcefully they contract.
76
76) Afterload is described as:
A) the ability to generate tension.
B) the force the ventricles must overcome to eject blood into their respective arteries.
C) the length or degree of stretch of the sarcomeres in the ventricular cells before they contract.
D) the amount of blood that has drained into the ventricle by the end of the filling phase.
B) the force the ventricles must overcome to eject blood into their respective arteries.
77
```
77) Inotropic agents affect:
A) contractility.
B) depolarization.
C) heart rate.
D) stroke volume.
```
A) contractility.
78
```
78) Which of the following is a chronotropic agent that decreases heart rate?
A) glucagon
B) norepinephrine
C) acetylcholine
D) epinephrine
```
C) acetylcholine
79
```
79) Which cranial nerves have a negative chronotropic effect on heart rate?
A) glossopharyngeal nerves (CN IX)
B) vagus nerves (CN X)
C) trochlear nerves (CN IV)
D) hypoglossal nerves (CN XII)
```
B) vagus nerves (CN X)
80
```
80) Which hormone decreases cardiac output by decreasing blood volume and preload?
A) atrial natriuretic peptide (ANP)
B) aldosterone
C) antidiuretic hormone (ADH)
D) norepinephrine
```
A) atrial natriuretic peptide (ANP)
81
81) The left side of the heart is often called the systemic pump due to blood flow to the body
TRUE
82
82) From superficial to deep, the pericardial sac consists of the fibrous pericardium, visceral pericardium, parietal pericardium, and the epicardium.
FALSE
83
83) The left ventricle has greater muscle mass than the right ventricle since it pumps against greater resistance.
TRUE
84
84) Desmosomes present between adjacent cardiac muscle cells allow ions to rapidly pass from one cell to another, permitting communication among cardiac muscle cells.
FALSE
85
85) The cardiac conduction system is normally regulated by a population of pacemaker cells known as the sinoatrial (SA) node.
TRUE
86
86) Heart rate can be determined by measuring the time between two successive R waves on an electrocardiogram (ECG), known as the R-R interval.
TRUE
87
87) There are two phases of the cardiac cycle in which all four heart valves are open: the isovolumetric contraction phase and the isovolumetric relaxation phase.
FALSE
88
88) Pressure in the aorta is greater than pressure in the pulmonary trunk; therefore, the left ventricle has to generate a greater pressure than the right ventricle in order to eject blood from the heart.
TRUE
89
89) Stroke volume (SV) can be calculated by subtracting the end-diastolic volume (EDV) from the end-systolic volume (ESV).
FALSE
90
90) The sympathetic nervous system increases cardiac output by increasing both heart rate and stroke volume.
TRUE
91
91) The sinoatrial (SA) node fires more rapidly at higher body temperatures, increasing cardiac output.
TRUE
92
92) Identify the right atrium.
| SEE DIAGRAM OF HEART
B
93
93) Identify the left ventricle.
| SEE DIAGRAM OF HEART
J
94
94) Identify the papillary muscle.
| SEE DIAGRAM OF HEART
I
95
95) Identify the pulmonary trunk.
| SEE DIAGRAM OF HEART
E
96
96) Identify the interventricular septum.
| SEE DIAGRAM OF HEART
K
97
97) Identify the mitral (bicuspid) valve.
| SEE DIAGRAM OF HEART
G
98
105) Explain how the right side and left side of the heart cooperate as a double pump.
The heart is divided functionally into right and left sides. The right side of the heart is sometimes called the pulmonary pump while the left side of the heart is sometimes called the systemic pump. The right side of the heart pumps blood into a series of blood vessels leading to and within the lungs for gas exchange, collectively called the pulmonary circuit. The left side of the heart receives oxygenated blood from the pulmonary veins and pumps it into the blood vessels that serve the rest of the body through the systemic circuit for another gas exchange event.
99
106) Determine the effects to blood flow if a heart attack has caused damage to the left side of the heart.
The left side of the heart, often called the systemic pump, receives oxygenated blood from the pulmonary veins and pumps it into the blood vessels that serve the rest of the body, collectively called the systemic circuit. In the systemic circuit, arteries deliver oxygenated blood to the smallest blood vessels, the systemic capillaries. Here gas exchange occurs: Oxygen diffuses from the blood into the tissues, and carbon dioxide diffuses from the tissues into the blood. If the left side of the heart has been damaged, delivery of oxygenated blood to the body's cells and tissues may be impaired.
100
107) Describe the structures and functions of the two layers that compose the pericardium surrounding the heart.
The pericardium is a sac with two components: the fibrous pericardium, a tough outer layer that attaches the heart to surrounding structures, and the serous pericardium, a thin inner serous membrane that produces serous fluid. The fibrous pericardium is composed of collagen bundles that make it tough and enable it to anchor the heart to structures such as the diaphragm and the great vessels. The collagen bundles also give the fibrous pericardium low distensibility. It doesn't change shape or size considerably when stretching forces are applied. This helps to prevent the chambers of the heart from overfilling with blood. The serous pericardium is composed of an outer parietal layer and an inner visceral layer. The parietal pericardium is fused to the inner surface of the fibrous pericardium. When the parietal pericardium reaches the great vessels, it folds under itself to form another layer that directly adheres to the heart, the visceral pericardium (epicardium).
101
108) Describe the coronary circulation.
The heart is supplied and drained by a set of blood vessels collectively called the coronary circulation. The right and left coronary arteries branch off the ascending aorta and deliver oxygenated blood to the coronary capillary beds, where gas and nutrient exchange takes place within the myocardium. Then the deoxygenated blood drains from capillaries into a series of coronary veins. Generally, the majority of the heart's veins empty into a large venous structure on the posterior heart, called the coronary sinus. The coronary sinus drains into the posterior right atrium.
102
109) Explain the benefit of anastomoses in coronary artery circulation.
Anastomoses are systems of channels formed between blood vessels. Coronary arteries may form anastomoses with one another, with branches from the pericardium, or even with arteries outside the coronary circulation entirely. The benefit of anastomoses in coronary circulation comes when blood flow to the myocardium is insufficient. Occasionally, new anastomoses will form to provide alternate routes of blood flow, known as collateral circulation, to the myocardium. Collaterals help protect muscle cells from damage that could result from blocked vessels.
103
110) Discuss the location and function of valves in the heart.
Right and left atrioventricular valves, present between the atria and ventricles, prevent the backward flow of blood into the atria when the ventricles contract. One semilunar valve is located between the left ventricle and the aorta while another semilunar valve is situated between the right ventricle and the pulmonary trunk. These semilunar valves prevent the backward flow of blood from the pulmonary trunk and aorta into the ventricles when the ventricles relax as a result of higher pressure in the arteries and gravity.
104
111) Predict the effects on valve function and blood flow through the heart for a patient who has ruptured chordae tendineae that anchor the mitral valve.
For a patient who has ruptured chordae tendineae anchoring the mitral valve, the valve may not be able to adequately prevent the backward flow of blood from the left ventricle into the left atrium during ventricular contraction. The tendon-like chordae tendineae anchor the atrioventricular valves, such as the mitral valve, to papillary muscles in the ventricles. The papillary muscles contract just before the ventricles begin ejecting blood. Tension on the chordae tendineae keeps the valves closed and prevents the cusps on the atrioventricular valves from everting.
105
112) Explain how cardiac contractile cells differ from cardiac pacemaker cells.
Cardiac contractile cells are striated cardiac muscle cells that respond to excitation from cardiac pacemaker cells by conducting an action potential and contracting. Cardiac pacemaker cells are noncontractile and nonstriated cardiac muscle cells that coordinate electrical activity rhythmically. They spontaneously generate action potentials that trigger cardiac contractile cells to have action potentials, known as autorhythmicity. Cardiac pacemaker cells do not require stimulation from the nervous system to generate action potentials.
106
113) Explain the significance of the plateau period during the action potential of a cardiac contractile cell.
The plateau period of contractile cell action potential slows the heart rate, allows the heart to fill with blood, increases the strength of the heart's contraction, and prevents tetany by lengthening the heart's refractory period. The prevention of tetany allows the heart to relax and the ventricles to refill with blood before the cardiac muscle cells are stimulated to contract again.
107
114) Predict the effects of hypocalcemia (low blood calcium ion levels) on the strength and length of contraction in a cardiac contractile cell.
Calcium ions normally enter the cardiac contractile cells as potassium ions continue to leave during the plateau phase in order to slow the heart rate and allow the heart to fill with blood. Normally, as calcium ions enter and potassium ions leave, the net membrane potential remains largely unchanged. However, in the case of hypocalcemia, the balance of ions entering and leaving would be disturbed. Since more potassium ions would be leaving than calcium ions entering, the cardiac contractile cell would not able to maintain a net charge of 0 mV. Thus, the length of the action potential would be shorter, the contraction potentially less forceful, and the heart would have less of an opportunity to fill with blood between action potentials.
108
115) Describe the pathway of the action potential through the cardiac conduction system.
Under normal conditions, the sinoatrial (SA) node generates an action potential that spreads to the atrioventricular (AV) node. Conduction slows once the action potential reaches the AV node and bundle due to a low number of gap junctions between AV nodal cells and the presence of nonconducting fibrous skeleton that surrounds the AV node. During this time, the atria depolarize and contract before the ventricles, giving the ventricles time to fill with blood. The action potential is conducted from the AV bundle to the right and left bundle branches. Depolarization spreads to the Purkinje fibers and then to the cardiac contractile muscle cells of the ventricles. As a result, the ventricles contract and blood is ejected from the heart through the aorta and pulmonary trunk.
109
116) Predict the effect on the ventricles if the AV node delay was shorter than normal.
Ventricles would not have the opportunity to fill with blood before contraction if the AV node delay was shorter than normal. The action potential may flow backward from the AV bundle into the AV node and atria as well. AV node delay is the time it takes for the action potential to spread from the SA node to the AV bundle. This time delay allows the atria an opportunity to depolarize and contract before the ventricles, giving the ventricles time to fill with blood. The AV node delay also prevents current from flowing backward from the AV bundle into the AV node and atria.
110
117) Explain why the QRS wave on an electrocardiogram (ECG) is normally larger than a P wave.
The QRS wave on an electrocardiogram is normally much larger in magnitude than the P wave because of the size differences between the atria and ventricles. The ventricles have greater cardiac muscle mass than the atria. Thus, the amplitude of their respective depolarizations correlates to their sizes.
111
118) Define the terms diastole and systole.
Each cardiac cycle consists of one period of relaxation known as diastole and one period of contraction known as systole for each set of chambers of the heart.
112
119) List the four phases of the cardiac cycle.
The four phases of the cardiac cycle are the 1) ventricular filling phase, 2) isovolumetric contraction phase, 3) ventricular ejection phase, 4) isovolumetric relaxation phase.
113
120) Summarize the two phases of the cardiac cycle during which all four heart valves are briefly closed.
The first phase during which all four heart valves are closed, known as the isovolumetric contraction phase, occurs at the beginning of ventricular systole. Pressure rises in the ventricles as they begin to contract. The high pressure closes the AV valves, producing the heart sound S1. Since ventricular pressure is not yet great enough to push open the semilunar valves, they remain closed. Ventricular volume does not change during this shortest phase of the cardiac cycle. The second phase during which all four heart valves are closed, known as the isovolumetric relaxation phase, occurs at the beginning of ventricular diastole. Pressure declines in the ventricles causing the semilunar valves to snap shut, producing the heart sound S2. The pressure in the ventricles is still somewhat higher than that in the atria, so the AV valves remain closed. Once again, ventricular volume does not change during this brief phase.
114
121) Explain how to calculate cardiac output (CO).
To determine cardiac output for a ventricle, we need to know both its stroke volume and heart rate. Stroke volume (SV) can be easily calculated by subtracting the amount of blood in the ventricle at the end of a contraction (the end-systolic volume, or ESV) from the amount of blood in the ventricle after it has filled during diastole (end-diastolic volume, or EDV). In an average heart, the resting stroke volume is equal to about 70 ml while the resting heart rate (HR) averages 60-80 cardiac cycles per minute. In summary, the calculation for cardiac output is:
CO = HR × SV.
115
122) Describe the Frank-Starling law.
According to the Frank-Starling law, the more the ventricular muscle cells are stretched, the more forcefully they contract. The relationship between contraction and stroke volume ensures that the volume of blood discharged from the heart is equal to the volume that enters it.
116
123) Discuss the chronotropic effects of the sympathetic and parasympathetic nervous systems on the heart.
The sympathetic nervous system releases a neurotransmitter, norepinephrine, which has a positive chronotropic effect on the heart. Due to the influence of the sympathetic nervous system, the sinoatrial (SA) node fires more quickly and the calcium ion concentration in the cardiac muscle cells increases. Both effects increase stroke volume, heart rate, and cardiac output. The parasympathetic nervous system releases a neurotransmitter, acetylcholine, from the vagus nerves (CN X). Acetylcholine has a negative chronotropic effect on the heart by slowing the rate of the sinoatrial (SA) node. Thus, heart rate and cardiac output decreases.
117
124) Trace the pathway of blood flow through the heart. Begin and end the pathway with the systemic capillaries.
The blood flow through the heart is as follows: 1) Systemic capillaries deliver oxygen to body cells. 2) Systemic veins return deoxygenated blood to the right atrium. 3) Blood passes from the right atrium through the tricuspid valve to the right ventricle. 4) The right ventricle pumps blood through the pulmonary valve to the pulmonary trunk. 5) The pulmonary trunk delivers blood to the right and left pulmonary arteries and then pulmonary capillaries of the left and right lungs, where blood becomes oxygenated. 6) The pulmonary veins return oxygenated blood to the left atrium. 7) Blood passes from the left atrium through the mitral (bicuspid) valve to the left ventricle. 8) The left ventricle pumps blood through the aortic valve to the aorta. 9) The aorta delivers blood to the systemic arteries and then capillaries.
118
125) Discuss the five waves seen on an electrocardiogram (ECG) and explain what they represent.
The five waves seen on an electrocardiogram (ECG) are the P wave, QRS wave, and the T wave. The P wave represents the depolarization of all cells in the atria except for the sinoatrial (SA) node and is normally an upward deflection. The QRS wave represents ventricular depolarization and is actually three separate waves. The Q wave is the first downward deflection, the R wave is the large upward deflection, and the S wave is the following downward deflection. The T wave follows the S wave of the QRS complex and represents ventricular repolarization. The T wave is normally an upward deflection.
119
126) An electrocardiogram (ECG) shows extra P waves. Determine and discuss the part of the conduction pathway that is not working.
Extra P waves indicate that some action potentials from the sinoatrial (SA) node are not being conducted through the atrioventricular (AV) node at all. Extra P waves are characteristic of heart block.
120
127) Predict the effect on the length of the R-R interval of an electrocardiogram (ECG) if a patient experiences bradycardia.
The R-R interval is the time between two successive R waves on the electrocardiogram (ECG). This interval represents the entire duration of the generation and spread of an action potential through the heart, and can be measured to determine the heart rate. Bradycardia is a heart rate slower than 60 beats per minute. The length between successive R waves will increase as the heart rate slows due to bradycardia.
121
128) A patient learns he has a heart murmur. His physician hears abnormal sounds during the S1 heart sound. Determine a potential cause of his heart murmur.
This patient probably has a heart murmur caused by a defective valve. Since his physician hears abnormal sounds during the timing for the S1 heart sound, his defective valve is either the tricuspid valve or the mitral (bicuspid) valve. The S1 sound, or "lub" is heard when the atrioventricular (AV) valves (tricuspid and mitral valves) close.
122
129) Calculate cardiac output given an end-diastolic volume of 140 ml, an end-systolic volume of 60 ml, and a heart rate of 85 beats/minute.
```
First, determine stroke volume. Stroke volume can be easily calculated by subtracting the amount of blood in the ventricle at the end of a contraction (the end-systolic volume, or ESV) from the amount of blood in the ventricle after it has filled during diastole (end-diastolic volume, or EDV).
SV =EDV−ESV
= 140 ml − 60 ml
= 80 ml
Next, determine cardiac output. To find the cardiac output, you simply multiply the heart rate by the stroke volume.
CO =HR×SV
= 85 beats/minute × 80 ml
= 6800 ml/min (or 6.8 L/min)
```
