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Chapter 20 the heart Flashcards

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1
Q

The heart contributes to homeostasis by

A

pumping blood through blood vessels to the tissues of the body to deliver oxygen and nutrients and remove wastes.

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2
Q

the cardiovascular system consists of

A

the blood, the heart, and blood vessels.

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3
Q

For blood to reach body cells and exchange materials with them,

A

it must be pumped continuously by the heart through the body’s blood vessels.

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4
Q

The heart beats about

A

100,000 times every day, which adds up to about 35 million beats in a year, and approximately 2.5 billion times in an average lifetime

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5
Q

The right side of the heart pumps blood through

A

the lungs, enabling blood to pick up oxygen and unload carbon dioxide.

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6
Q

your heart pumps more than about

A

14,000 liters (3600 gal) of blood in a day, or 5 million liters (1.3 million gal) in a year.

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7
Q

cardiology

A

The scientific study of the normal heart and the diseases associated with it is known as

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8
Q

the heart is relatively

A

small, roughly the same size (but not the same shape) as your closed fist

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9
Q

describe the dimensions and size of the heart

A

It is about 12 cm (5 in.) in its long axis, 9 cm (3.5 in.) wide at its broadest point, and 6 cm (2.5 in.) in depth (anterior to posterior), with an average mass of 250 g (8 oz) in adult females and 300 g (10 oz) in adult males.

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10
Q

The heart rests on

A

the diaphragm, near the midline of the thoracic cavity.

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11
Q

The heart lies in the

A

mediastinum (mē′-dē-as-TĪ-num), an anatomical region that extends from the sternum to the vertebral column, from the first rib to the diaphragm, and between the lungs (Figure 20.1a).

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12
Q

About two-thirds of the mass of the heart lies

A

to the left of the body’s midline

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13
Q

You can visualize the heart as

A

a cone lying on its side

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14
Q

The pointed apex is formed by the __________________and rests on the __________________

A

tip of the left ventricle (a lower chamber of the heart)
diaphragm

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15
Q

The base of the heart is

A

opposite the apex and is its posterior aspect.

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16
Q

The base of the heart is formed by

A

the atria (upper chambers) of the heart, mostly the left atrium (see Figure 20.3c).

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17
Q

The anterior surface of the heart .

A

is deep to the sternum and ribs

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18
Q

The inferior surface of the heart is the part of the heart

A

between the apex and right surface and rests mostly on the diaphragm

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19
Q

The right surface of the heart faces

A

the right lung and extends from the inferior surface to the base.

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20
Q

The left surface of the heart

A

faces the left lung and extends from the base to the apex.

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21
Q

pericardium

A

The membrane that surrounds and protects the heart

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22
Q

What is the function of the pericardium

A

It confines the heart to its position in the mediastinum, while allowing sufficient freedom of movement for vigorous and rapid contraction.

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23
Q

The pericardium consists of two main parts:

A

(1) the fibrous pericardium and (2) the serous pericardium

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24
Q

the fibrous pericardium

A

is superficial and composed of tough, inelastic, dense irregular connective tissue

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25
Q

What is the function of the fibrous pericardium

A

The fibrous pericardium prevents overstretching of the heart, provides protection, and anchors the heart in the mediastinum

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26
Q

The fibrous pericardium near the apex of the heart is

A

partially fused to the central tendon of the diaphragm and therefore movement of the diaphragm, as in deep breathing, facilitates the movement of blood by the heart.

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27
Q

The pericardium is

A

a triple-layered sac that surrounds and protects the heart.

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28
Q

Cardiopulmonary resuscitation (CPR) (kar-dē-ō-PUL-mo-nar′-ē rē-sus-i-TĀ-shun) refers to

A

an emergency procedure for establishing a normal heartbeat and rate of breathing

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29
Q

serous pericardium is

A

a deeper, thinner, more delicate mesothelial membrane than the fibrous pericardium that forms a double layer around the heart

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30
Q

The outer parietal layer of the serous pericardium

A

lines the inside of the fibrous pericardium.

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31
Q

The inner visceral layer of the serous pericardium

A

is one of the layers of the heart wall and adheres tightly to the surface of the heart.

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32
Q

The inner visceral layer of the serous pericardium,

A

is also called the epicardium

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33
Q

Between the parietal and visceral layers of the serous pericardium

A

is a thin film of a few mililiters of lubricating serous fluid. This slippery secretion of the pericardial cells, known as pericardial fluid, reduces friction between the layers of the serous pericardium as the heart moves.

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34
Q

the pericardial cavity.

A

The space that contains the few milliliters of pericardial fluid

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35
Q

Inflammation of the pericardium is called

A

pericarditis

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36
Q

The most common type, acute pericarditis,

A

begins suddenly and has no known cause in most cases but is sometimes linked to a viral infection.

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37
Q

Chronic pericarditis

A

begins gradually and is long-lasting

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38
Q

The wall of the heart consists of three layers (Figure 20.2a):

A

the epicardium (external layer), the myocardium (middle layer), and the endocardium (inner layer).

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39
Q

The epicardium is composed of two

A

tissue layers.

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40
Q

The outermost layer of the epicardium is called the visceral layer of the serous pericardium. This layer is

A

Thin and transparent and made of mesothelium

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41
Q

Beneath the mesothelium is

A

a variable layer of delicate fibroelastic tissue and adipose tissue. the adipose tissue predominates and becomes thickest over the ventricular surfaces, where it houses the major coronary and cardiac vessels of the heart.

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42
Q

The epicardium imparts

A

a smooth, slippery texture to the outermost surface of the heart.

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43
Q

The epicardium contains

A

blood vessels, lymphatics, and nerves that supply the myocardium.

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44
Q

The middle myocardium (mī′-ō-KAR-dē-um; myo- = muscle) is responsible for

A

the pumping action of the heart and is composed of cardiac muscle tissue.

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45
Q

The myocardium makes up

A

about 95 percent of the heart wall

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46
Q

The cardiac muscle fibers are organized in

A

bundles that swirl diagonally around the heart and generate the strong pumping actions of the heart

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47
Q

Although it is striated like skeletal muscle, recall that

A

cardiac muscle is involuntary like smooth muscle.

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48
Q

Myocarditis (mī-ō-kar-DĪ-tis) is

A

an inflammation of the myocardium that usually occurs as a complication of a viral infection, rheumatic fever, or exposure to radiation or certain chemicals or medications

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49
Q

Endocarditis (en′-dō-kar-DĪ-tis) refers to

A

an inflammation of the endocardium and typically involves the heart valves. Most cases are caused by bacteria (bacterial endocarditis).

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50
Q

The innermost endocardium (en′-dō-KAR-dē-um; endo- = within) is

A

a thin layer of endothelium overlying a thin layer of connective tissue.

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51
Q

the endocaardium

A

provides a smooth lining for the chambers of the heart and covers the valves of the heart.

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52
Q

The endocardium is continuous with

A

the endothelial lining of the large blood vessels attached to the heart.

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53
Q

The heart has

A

four chambers.

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54
Q

atria

A

The two superior receiving chambers

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55
Q

ventricles (= little bellies).

A

the two inferior pumping chambers

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56
Q

The paired atria

A

receive blood from blood vessels returning blood to the heart, called veins,

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57
Q

the ventricles

A

eject the blood from the heart into blood vessels called arteries

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58
Q

auricle

A

a wrinkled pouchlike structure On the anterior surface of each atrium

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59
Q

What is the function of the auricles on each atrium

A

Each auricle slightly increases the capacity of an atrium so that it can hold a greater volume of blood

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60
Q

sulci (SUL-sī),

A

a series of grooves on the surface of the heart that contain coronary blood vessels and a variable amount of fat

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61
Q

Each sulcus (SUL-kus; singular)

A

marks the external boundary between two chambers of the heart.

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62
Q

The deep coronary sulcus (coron- = resembling a crown)

A

encircles most of the heart and marks the external boundary between the superior atria and inferior ventricles.

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63
Q

The anterior interventricular sulcus (in′-ter-ven-TRIK-ū-lar)

A

is a shallow groove on the anterior surface of the heart that marks the external boundary between the right and left ventricles on the anterior aspect of the heart.

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64
Q

the anterior ventricular sulcus continues around to the posterior surface of the heart as

A

the posterior interventricular sulcus, which marks the external boundary between the ventricles on the posterior aspect of the heart

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65
Q

Sulci are

A

grooves that contain blood vessels and fat and that mark the external boundaries between the various chambers.

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66
Q

The right atrium

A

forms the right surface of the heart and receives blood from three veins: the superior vena cava, inferior vena cava, and coronary sinus (Figure 20.4a).

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67
Q

Veins always carry blood

A

toward the heart.

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68
Q

The inside of the posterior wall of the right atrium

A

is smooth;

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69
Q

the inside of the anterior wall of the right atrium

A

is rough due to the presence of muscular ridges called pectinate muscles

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70
Q

The pectinate muscles

A

extend into the auricle

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71
Q

Between the right atrium and left atrium is

A

a thin partition called the interatrial septum

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72
Q

A prominent feature of the interatrial septum is an oval depression called the

A

fossa ovalis

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73
Q

fossa ovalis,

A

the remnant of the foramen ovale, an opening in the interatrial septum of the fetal heart that normally closes soon after birth

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74
Q

Blood passes from the right atrium into the right ventricle through

A

a valve that is called the right atrioventricular (tricuspid) valve

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75
Q

why is the right atrioventricular valve also called the tricuspid valve

A

because it consists of three cusps or leaflets

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76
Q

The valves of the heart are composed of

A

dense connective tissue covered by endocardium.

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77
Q

Blood flows into the right atrium through

A

the superior vena cava, inferior vena cava, and coronary sinus and into the left atrium through four pulmonary veins.

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78
Q

The right ventricle is

A

about 4–5 mm (0.16–0.2 in.) in average thickness and forms most of the anterior surface of the heart.

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79
Q

trabeculae carneae

A

a series of ridges formed by raised bundles of cardiac muscle fibers

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80
Q

The cusps of the right atrioventricular valve are connected to

A

tendonlike cords, called the chordae tendineae

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81
Q

The chordae tendineae

A

are connected to cone-shaped trabeculae carneae called papillary muscles

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82
Q

Internally, the right ventricle is separated from the left ventricle by

A

a partition called the interventricular septum.

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83
Q

Blood passes from the right ventricle through

A

the pulmonary valve into a large artery called the pulmonary trunk, which divides into right and left pulmonary arteries and carries blood to the lungs.

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84
Q

Arteries always take blood

A

away from the heart (a mnemonic to help you: artery = away).

85
Q

The left atrium

A

is about the same thickness as the right atrium and forms most of the base of the heart

86
Q

The left atrium recieves

A

receives blood from the lungs through four pulmonary veins.

87
Q

Like the right atrium, the inside of the left atrium has

A

a smooth posterior wall

88
Q

Because pectinate muscles are confined to the auricle of the left atrium,

A

the anterior wall of the left atrium also is smooth.

89
Q

Blood passes from the left atrium into the left ventricle through

A

the left atrioventricular (bicuspid or mitral) valve (bi- = two)

90
Q

The left ventricle is

A

the thickest chamber of the heart, averaging 10–15 mm (0.4–0.6 in.), and forms the apex of the heart

91
Q

Like the right ventricle, the left ventricle

A

contains trabeculae carneae and has chordae tendineae that anchor the cusps of the bicuspid valve to papillary muscles

92
Q

Blood passes from the left ventricle through

A

the aortic valve into the ascending aorta

93
Q

Some of the blood in the aorta flows into the

A

coronary arteries, which branch from the ascending aorta and carry blood to the heart wall. The remainder of the blood passes into the aortic arch and descending aorta

94
Q

Branches of the aortic arch and descending aorta

A

carry blood throughout the body

95
Q

During fetal life,

A

a temporary blood vessel, called the ductus arteriosus, shunts blood from the pulmonary trunk into the aorta. Hence, only a small amount of blood enters the nonfunctioning fetal lungs

96
Q

The ductus arteriosus normally

A

closes shortly after birth, leaving a remnant known as the ligamentum arteriosum (lig′-a-MEN-tum ar-ter-ē-Ō-sum), which connects the aortic arch and pulmonary trunk

97
Q

The thickness of the myocardium of the four chambers

A

varies according to each chamber’s function

98
Q

The thin-walled atria deliver blood

A

under less pressure into the adjacent ventricles.

99
Q

Because the ventricles pump blood under higher pressure over greater distances

A

, their walls are thicker

100
Q

Although the right and left ventricles act as two separate pumps that simultaneously eject equal volumes of blood,

A

the right side has a much smaller workload. It pumps blood a shorter distance to the lungs at lower pressure, and the resistance to blood flow is small.

101
Q

The left ventricle pumps blood

A

a greater distance to all other parts of the body at higher pressure, and the resistance to blood flow is larger.Therefore, the left ventricle works much harder than the right ventricle to maintain the same rate of blood flow.

102
Q

The anatomy of the two ventricles confirms this functional difference—

A

the muscular wall of the left ventricle is considerably thicker than the wall of the right ventricle

103
Q

the perimeter of the lumen (space) of the left ventricle is

A

roughly circular, in contrast to that of the right ventricle, which is somewhat crescent-shaped.

104
Q

In addition to cardiac muscle tissue, the heart wall also contains dense connective tissue that forms

A

the fibrous skeleton of the heart

105
Q

Essentially, the fibrous skeleton consists of

A

four dense connective tissue rings that surround the valves of the heart, fuse with one another, and merge with the interventricular septum

106
Q

In addition to forming a structural foundation for the heart valves, the fibrous skeleton prevents

A

overstretching of the valves as blood passes through them.

107
Q

the fibrous skeleton of the heart

A

serves as a point of insertion for bundles of cardiac muscle fibers and acts as an electrical insulator between the atria and ventricles.

108
Q

As each chamber of the heart contracts,

A

it pushes a volume of blood into a ventricle or out of the heart into an artery.

109
Q

Valves open and close in response to

A

pressure changes as the heart contracts and relaxes

110
Q

Each of the four valves helps ensure the one-way flow of blood by

A

opening to let blood through and then closing to prevent its backflow

111
Q

atrioventricular (AV) valves

A

The valves located between an atrium and a ventricle

112
Q

When an AV valve is open,

A

the rounded ends of the cusps project into the ventricle.

113
Q

When the ventricles are relaxed,

A

the papillary muscles are relaxed, the chordae tendineae are slack, and blood moves from a higher pressure in the atria to a lower pressure in the ventricles through open AV valves

114
Q

When the ventricles contract,

A

the pressure of the blood drives the cusps upward until their edges meet and close the opening (Figure 20.6b, e). At the same time, the papillary muscles contract, which pulls on and tightens the chordae tendineae. This prevents the valve cusps from everting (opening into the atria) in response to the high ventricular pressure.

115
Q

If the AV valves or chordae tendineae are damaged,

A

blood may regurgitate (flow back) into the atria when the ventricles contract.

116
Q

Heart valves function

A

prevent the backflow of blood.

117
Q

the aortic and pulmonary valves are known as

A

the semilunar (SL) valves (sem-ē-LOO-nar; semi- = half; -lunar = moon-shaped) because they are made up of three crescent moon–shaped cusps

118
Q

In the semilunar valves

A

Each cusp attaches to the arterial wall by its convex outer margin

119
Q

The SL valves allow

A

ejection of blood from the heart into arteries but prevent backflow of blood into the ventricles.

120
Q

in the semilunar valves

A

The free borders of the cusps project into the lumen of the artery

121
Q

When the ventricles contract in semilunar valves,

A

pressure builds up within the chambers. The semilunar valves open when pressure in the ventricles exceeds the pressure in the arteries, permitting ejection of blood from the ventricles into the pulmonary trunk and aorta

122
Q

As the ventricles relax in semilunar valves

A

blood starts to flow back toward the heart. This backflowing blood fills the valve cusps, which causes the free edges of the semilunar valves to contact each other tightly and close the opening between the ventricle and artery

123
Q

Surprisingly, there are no valves guarding

A

the junctions between the venae cavae and the right atrium or the pulmonary veins and the left atrium.

124
Q

As the atria contract,

A

a small amount of blood does flow backward from the atria into these vessels. However, backflow is minimized by a different mechanism: as the atrial muscle contracts, it compresses and nearly collapses the weak walls of the venous entry points. Furthermore, the weak pumping pressure of the atria is not strong enough to overcome the hydrostatic pressure in the veins.

125
Q

In postnatal (after birth) circulation,

A

the heart pumps blood into two closed circuits with each beat—systemic circulation and pulmonary circulation

126
Q

the systemic circulation and the pulmonary circulation are arranged

A

are arranged in series: The output of one becomes the input of the other, as would happen if you attached two garden hoses

127
Q

The left side of the heart is the pump for

A

systemic circulation; it receives bright red oxygenated (oxygen-rich) blood from the lungs.

128
Q

The left ventricle ejects blood into

A

the aorta

129
Q

After The left ventricle ejects blood into the aorta. From the aorta, the blood

A

divides into separate streams, entering progressively smaller systemic arteries that carry it to all organs throughout the body—except for the pulmonary alveoli (air sacs) of the lungs, which are supplied by the pulmonary circulation

130
Q

In systemic tissues, arteries give rise to ,

A

smaller-diameter arterioles

131
Q

arterioles, finally lead into

A

extensive beds of systemic capillaries

132
Q

Exchange of nutrients and gases occurs

A

across the thin capillary walls, Blood unloads O2 (oxygen) and picks up CO2 (carbon dioxide).

133
Q

In most cases, blood flows through only one capillary and then

A

enters a systemic venule

134
Q

Venules carry

A

deoxygenated (oxygen-poor) blood away from tissues and merge to form larger systemic veins. Ultimately the blood flows back to the right atrium.

135
Q

The right side of the heart pumps

A

deoxygenated blood into the pulmonary circulation to the pulmonary alveoli of the lungs

136
Q

The right side of the heart is the pump for

A

pulmonary circulation; it receives all of the dark-red deoxygenated blood returning from the systemic circulation.

137
Q

Blood ejected from the right ventricle flows into

A

the pulmonary trunk

138
Q

The pulmonary trunk branches into

A

pulmonary arteries that carry blood to the right and left lungs.

139
Q

In pulmonary capillaries, around pulmonary alveoli,

A

blood unloads CO2, which is exhaled, and picks up O2 from inhaled air. The freshly oxygenated blood then flows into pulmonary veins and returns to the left atrium.

140
Q

Nutrients are not able to diffuse quickly enough from blood in the chambers of the heart to

A

supply all layers of cells that make up the heart wall.

141
Q

since Nutrients are not able to diffuse quickly enough from blood in the chambers of the heart to supply all layers of cells that make up the heart wall.

A

the myocardium has its own network of blood vessels, the coronary circulation or cardiac circulation (coron- = crown).

142
Q

The coronary arteries branch from

A

the ascending aorta and encircle the heart as a crown encircles the head

143
Q

While the heart is contracting,

A

little blood flows in the coronary arteries because they are squeezed shut.

144
Q

When the heart relaxes

A

the high pressure of blood in the aorta propels blood through the coronary arteries, into capillaries, and then into coronary veins

145
Q

stenosis

A

A narrowing of a heart valve opening that restricts blood flow is known as

146
Q

insufficiency (in′-su-FISH-en-sē) or incompetence

A

failure of a valve to close completely

147
Q

In mitral (left atrioventricular) stenosis,

A

scar formation or a congenital defect causes narrowing of the left atrioventricular valve

148
Q

One cause of mitral (left atrioventricular) insufficiency, in which there is backflow of blood from the left ventricle into the left atrium, is

A

mitral (left atrioventricular) valve prolapse (MVP).

149
Q

In MVP

A

one or both cusps of the left atrioventricular valve protrude into the left atrium during ventricular contraction.

150
Q

In aortic stenosis

A

the aortic valve is narrowed

151
Q

in aortic insufficiency

A

there is backflow of blood from the aorta into the left ventricle.

152
Q

Two coronary arteries, the left and right coronary arteries,

A

branch from the ascending aorta and supply oxygenated blood to the myocardium

153
Q

The left coronary artery

A

passes inferior to the left auricle and divides into the anterior interventricular and circumflex arteries.

154
Q

The anterior interventricular artery or left anterior descending (LAD) artery

A

is in the anterior interventricular sulcus and supplies oxygenated blood to the walls of both ventricles.

155
Q

The circumflex artery (SER-kum-fleks)

A

lies in the coronary sulcus and distributes oxygenated blood to the walls of the left ventricle and left atrium.

156
Q

The right coronary artery supplies

A

small branches (atrial branches) to the right atrium It continues inferior to the right auricle and ultimately divides into the posterior interventricular and marginal branches.

157
Q

The inferior (posterior) interventricular artery

A

follows the posterior interventricular sulcus and supplies the walls of the two ventricles with oxygenated blood.

158
Q

The marginal branch beyond the coronary sulcus

A

runs along the right margin of the heart and transports oxygenated blood to the wall of the right ventricle.

159
Q

The left and right coronary arteries

A

deliver blood to the heart

160
Q

; the coronary veins

A

drain blood from the heart into the coronary sinus.

161
Q

Most parts of the body

A

receive blood from branches of more than one artery, and where two or more arteries supply the same region, they usually connect.

162
Q

where two or more arteries supply the same region, they usually connect. These connections, are called

A

anastomoses

163
Q

anastomoses (a-nas′-tō-MŌ-sēs), provide

A

alternate routes, called collateral circulation, for blood to reach a particular organ or tissue.

164
Q

The myocardium contains many

A

anastomoses that connect branches of a given coronary artery or extend between branches of different coronary arteries. They provide detours for arterial blood if a main route becomes obstructed.

165
Q

After blood passes through the arteries of the coronary circulation,

A

it flows into capillaries, where it delivers oxygen and nutrients to the heart muscle and collects carbon dioxide and waste, and then moves into coronary veins

166
Q

Most of the deoxygenated blood from the myocardium

A

drains into a large vascular sinus in the coronary sulcus on the posterior surface of the heart, called the coronary sinus

167
Q

vascular sinus

A

a thin-walled vein that has no smooth muscle to alter its diameter

168
Q

The deoxygenated blood in the coronary sinus

A

empties into the right atrium.

169
Q

What veins flow into the coronary sinus

A

Great cardiac vein
Middle cardiac vein
small cardiac vein
anterior cardiac veins

170
Q

Describe the location and function of the great cardiac vein

A

in the anterior interventricular sulcus, which drains the areas of the heart supplied by the left coronary artery (left and right ventricles and left atrium)

171
Q

Describe the location and function of the middle cardiac vein

A

in the posterior interventricular sulcus, which drains the areas supplied by the inferior interventricular artery of the right coronary artery (left and right ventricles)

172
Q

Describe the location and function of the small cardiac vein

A

in the coronary sulcus, which drains the right atrium and right ventricle

173
Q

Describe the function of the anterior cardiac veins

A

drain the right ventricle and open directly into the right atrium

174
Q

When blockage of a coronary artery deprives the heart muscle of oxygen,

A

reperfusion (re′-per-FYŪ-zhun), the reestablishment of blood flow, may damage the tissue further

175
Q

why When blockage of a coronary artery deprives the heart muscle of oxygen, does reperfusion (re′-per-FYŪ-zhun), the reestablishment of blood flow, damage the tissue further

A

the formation of oxygen free radicals from the reintroduced oxygen.

176
Q

free radicals are

A

molecules that have an unpaired electron

177
Q

free radicals

A

cause chain reactions that lead to cellular damage and death.

178
Q

To counter the effects of oxygen free radicals,

A

body cells produce enzymes that convert free radicals to less reactive substances.

179
Q

What enzymes are produced to combat the effets of free radicals

A

superoxide dismutase (dis-MŪ-tās) and catalase (KAT-a-lās).

180
Q

nutrients such as vitamin E, vitamin C, beta-carotene, zinc, and selenium serve as antioxidants, which

A

remove oxygen free radicals from circulation.

181
Q

Partial obstruction of blood flow in the coronary arteries may cause

A

myocardial ischemia

182
Q

myocardial ischemia (is-KĒ-mē-a; ische- = to obstruct; -emia = in the blood),

A

a condition of reduced blood flow to the myocardium.

183
Q

Usually, ischemia causes

A

hypoxia (hī-POKS-ē-a = reduced oxygen supply), which may weaken cells without killing them.

184
Q

Silent myocardial ischemia, ischemic episodes without pain, is particularly dangerous because

A

the person has no forewarning of an impending heart attack.

185
Q

A complete obstruction to blood flow in a coronary artery may result in a

A

myocardial infarction (MI) (in-FARK-shun), commonly called a heart attack.

186
Q

Infarction is

A

the death of an area of tissue because of interrupted blood supply

187
Q

Compared with skeletal muscle fibers (cells), cardiac muscle fibers are

A

shorter in length and less circular in transverse section

188
Q

cardiac muscle fibers

A

exhibit branching, which gives individual cardiac muscle fibers a “stair-step” appearance

189
Q

in cardiac muscle fibers

A

Usually one centrally located nucleus is present, although an occasional cell may have two nuclei.

190
Q

The ends of cardiac muscle fibers connect to neighboring fibers by

A

irregular transverse thickenings of the sarcolemma called intercalated discs (in-TER-ka-lāt-ed; intercalat- = to insert between)

191
Q

intercalated discs contain

A

desmosomes, which hold the fibers together, and gap junctions, which allow muscle action potentials to conduct from one muscle fiber to its neighbors.

192
Q

Gap junctions allow

A

the entire myocardium of the atria or the ventricles to contract as a single, coordinated unit.

193
Q

Mitochondria are

A

larger and more numerous in cardiac muscle fibers than in skeletal muscle fibers.

194
Q

In a cardiac muscle fiber, mitochondria take up

A

25% of the cytosolic space; in a skeletal muscle fiber only 2% of the cytosolic space is occupied by mitochondria

195
Q

Cardiac muscle fibers have the same arrangement of ___________________as skeletal muscle fibers

A

actin and myosin, and the same bands, zones, and Z discs,

196
Q

The T (transverse) tubules of cardiac muscle are

A

wider but less abundant than those of skeletal muscle; the one T tubule per sarcomere is located at the Z disc

197
Q

The sarcoplasmic reticulum of cardiac muscle fibers is

A

somewhat smaller than the SR of skeletal muscle fibers. As a result, cardiac muscle has a smaller intracellular reserve of Ca2+.

198
Q

autorhythmic fibers

A

a network of specialized cardiac muscle fibers (cells) and The source of electrical activity in the heart

199
Q

autorythmic fibers are

A

self excitable

200
Q

Autorhythmic fibers repeatedly

A

generate action potentials that trigger heart contractions.

201
Q

During embryonic development, only about 1% of the cardiac muscle fibers

A

become autorhythmic fibers

202
Q

auto rythmic fibers have two main functions

A

They act as a natural pacemaker, setting the rhythm of electrical excitation that causes contraction of the heart.
They form the cardiac conduction system, a network of specialized cardiac muscle fibers that provide a path for each cycle of cardiac excitation to progress through the heart.

203
Q

The conduction system ensures that

A

cardiac chambers become stimulated to contract in a coordinated manner, which makes the heart an effective pump.

204
Q

Cardiac muscle fibers connect to neighboring fibers by

A

intercalated discs, which contain desmosomes and gap junctions.

205
Q

Where does the cardiac conduction system begin

A

Cardiac excitation normally begins in the sinuatrial (SA) node, located in the right atrial wall just inferior and lateral to the opening of the superior vena cava

206
Q

SA node cells do not have a stable resting potential. Rather,

A

they repeatedly depolarize to threshold spontaneously. The spontaneous depolarization is a pacemaker potential.

207
Q

What is the first step in the cardiac conduction system

A

When the pacemaker potential reaches threshold, it triggers an action potential (Figure 20.10b). Each action potential from the SA node propagates throughout both atria via gap junctions in the intercalated discs of atrial muscle fibers. Following the action potential, the two atria contract at the same time.

208
Q

in the cardiac conduction system what happens after the two atria contract

A

By conducting along atrial muscle fibers, the action potential reaches the atrioventricular (AV) node, located in the interatrial septum, just anterior to the opening of the coronary sinus

Bio 139 (4 decks)

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