Chapter 23 respiratory

Question 1

The respiratory system contributes to homeostasis by

Answer 1

providing for the exchange of gases—oxygen and carbon dioxide—among the atmospheric air, blood, and tissue cells. It also helps adjust the pH of body fluids.

Question 2

Your body’s cells continually use oxygen (O2) for

Answer 2

the metabolic reactions that generate ATP from the breakdown of nutrient molecules.

Question 3

Because an excessive amount of CO2 produces acidity that can be toxic to cells,

Answer 3

excess CO2 must be eliminated quickly and efficiently.

Question 4

The cardiovascular and respiratory systems cooperate to

Answer 4

supply O2 and eliminate CO2

Question 5

Failure of eitherthe cardiovascular system or the respiratory system disrupts homeostasis by

Answer 5

causing rapid death of cells from oxygen starvation and buildup of waste products.

Question 6

In addition to functioning in gas exchange, the respiratory system also participates in

Answer 6

regulating blood pH, contains receptors for the sense of smell, filters inspired air, produces sounds, and rids the body of some water and heat in exhaled air.

Question 7

As in the digestive and urinary systems, which will be covered in subsequent chapters, in the respiratory system there is

Answer 7

an extensive area of contact between the external environment and capillary blood vessels.

Question 8

respiration is

Answer 8

The process of supplying the body with O2 and removing CO2

Question 9

respiration has three basic steps

Answer 9

Pulmonary ventilation
external (pulmonary) respiration
internal (tissue) respiration

Question 10

Pulmonary ventilation (pulmon- = lung), or breathing, is

Answer 10

the inhalation (inflow) and exhalation (outflow) of air and involves the exchange of air between the atmosphere and the pulmonary alveoli of the lungs. Inhalation permits O2 to enter the lungs and exhalation permits CO2 to leave the lungs.

Question 11

External (pulmonary) respiration is

Answer 11

the exchange of gases between the pulmonary alveoli of the lungs and the blood in pulmonary capillaries across the respiratory membrane. In this process, pulmonary capillary blood gains O2 and loses CO2.

Question 12

Internal (tissue) respiration is

Answer 12

the exchange of gases between blood in systemic capillaries and tissue cells. In this step the blood loses O2 and gains CO2. Within cells, the metabolic reactions that consume O2 and give off CO2 during the production of ATP are termed cellular respiration

Question 13

The respiratory system (RES-pi-ra-tōr-ē) consists of

Answer 13

the nose, pharynx (throat), larynx (voice box), trachea (windpipe), bronchi, and lungs

Question 14

Structurally, the respiratory system consists of two parts:

Answer 14

(1) The upper respiratory system
(2) the lower respiratory system

Question 15

The upper respiratory system includes

Answer 15

the nose, nasal cavity, pharynx, and associated structures;

Question 16

the lower respiratory system includes

Answer 16

the larynx, trachea, bronchi, and lungs.

Question 17

Functionally, the respiratory system also consists of two parts.

Answer 17

(1) The conducting zone
2) the respiratory zone

Question 18

The conducting zone consists of

Answer 18

a series of interconnecting cavities and tubes both outside and within the lungs. These include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles

Question 19

What is the function of the conducting zone

Answer 19

to filter, warm, and moisten air and conduct it into the lungs.

Question 20

The respiratory zone consists of

Answer 20

tubes and tissues within the lungs where gas exchange occurs. These include the respiratory bronchioles, alveolar ducts, alveolar saccules (sacs), and pulmonary alveoi

Question 21

What is the main function of the respiratory zone

Answer 21

the main sites of gas exchange between air and blood.

Question 22

During respiration

Answer 22

the body is supplied with O2 and CO2 is removed.

Question 23

otorhinolaryngology

Answer 23

The branch of medicine that deals with the diagnosis and treatment of diseases of the ears, nose, and throat (ENT)

Question 24

What are the functions of the respiratory system

Answer 24

Provides for gas exchange: intake of O2 for delivery to body cells and removal of CO2 produced by body cells.
Helps regulate blood pH.
Contains receptors for sense of smell, filters inspired air, produces vocal sounds (phonation), and excretes small amounts of water and heat.

Question 25

The nose is

Answer 25

a specialized organ at the entrance of the respiratory system that consists of a visible external portion (external nose) and an internal portion inside the skull called the nasal cavity (internal nose).

Question 26

The external nose is

Answer 26

the portion of the nose visible on the face and consists of a supporting framework of bone and hyaline cartilage covered with muscle and skin and lined by a mucous membrane.

Question 27

the bony framework of the external nose consists of

Answer 27

The frontal bone, nasal bones, and maxillae

Question 28

The cartilaginous framework of the external nose consists of

Answer 28

several pieces of hyaline cartilage connected to each other and certain skull bones by fibrous connective tissue.

Question 29

The components of the cartilaginous framework are

Answer 29

the nasal septal cartilage, which forms the anterior portion of the nasal septum; the lateral nasal cartilages inferior to the nasal bones; and the alar cartilages (Ā-lar), which form a portion of the walls of the nostrils.

Question 30

Because it consists of pliable hyaline cartilage, the cartilaginous framework of the external nose is

Answer 30

somewhat flexible.

Question 31

On the undersurface of the external nose are

Answer 31

two openings called the nostrils (external nares) which lead into cavities called the nasal vestibules.

Question 32

The interior structures of the external nose have three functions:

Answer 32

(1) warming, moistening, and filtering incoming air; (2) detecting olfactory stimuli; and (3) modifying speech vibrations as they pass through the large, hollow resonating chambers.

Question 33

Resonance refers to

Answer 33

prolonging, amplifying, or modifying a sound by vibration.

Question 34

Rhinoplasty (RĪ-nō-plas′-tē; rhin = nose; -plasty = to mold or to shape), or “nose job,” is

Answer 34

a surgical procedure in which the shape of the external nose is altered.

Question 35

The nasal cavity (internal nose) is

Answer 35

a large space in the anterior aspect of the skull that lies inferior to the nasal bone and superior to the oral cavity; it is lined with muscle and mucous membrane

Question 36

A vertical partition, the nasal septum,

Answer 36

divides the nasal cavity into right and left sides.

Question 37

The anterior portion of the nasal septum consists primarily of

Answer 37

hyaline cartilage;

Question 38

The anterior portion of the nasal septum consists primarily of hyaline cartilage; the remainder is formed by

Answer 38

the vomer and the perpendicular plate of the ethmoid, maxillae, and palatine bones

Question 39

Anteriorly, the nasal cavity merges with the

Answer 39

external nose,

Question 40

posteriorly the nasal cavity communicates with

Answer 40

the pharynx through two openings called the choanae (kō-Ā-nē) or internal nares

Question 41

Ducts from the paranasal sinuses (which drain mucus) and the nasolacrimal ducts (which drain tears)

Answer 41

open into the nasal cavity.

Question 42

the paranasal sinuses are

Answer 42

cavities in certain cranial cavity and facial bones lined with mucous membrane that are continuous with the lining of the nasal cavity.

Question 43

Skull bones containing the paranasal sinuses are

Answer 43

the frontal, sphenoid, ethmoid, and maxillae

Question 44

Besides producing mucus, the paranasal sinuses serve as

Answer 44

resonating chambers for sound as we speak or sing.

Question 45

The lateral walls of the internal nose are formed by

Answer 45

the ethmoid, maxillae, lacrimal, palatine, and inferior nasal conchae bones (see Figure 7.9); the ethmoid bone also forms the roof.

Question 46

__________________________ form the floor of the internal nose.

Answer 46

The palatine bones and palatine processes of the maxillae, which together constitute the hard palate,

Question 47

As air passes through the nose,

Answer 47

it is warmed, filtered, and moistened, and olfaction occurs.

Question 48

The external nose has

Answer 48

a cartilaginous framework and a bony framework.

Question 49

The bony and cartilaginous framework of the nose help

Answer 49

to keep the nasal vestibule and nasal cavity patent, that is, open or unobstructed.

Question 50

The nasal cavity is divided into

Answer 50

a larger, inferior respiratory region and a smaller, superior olfactory region.

Question 51

The respiratory region of the nasal cavity is lined with

Answer 51

ciliated pseudostratified columnar epithelium with numerous goblet cells, which is frequently called the respiratory epithelium

Question 52

The anterior portion of the nasal cavity just inside the nostrils,

Answer 52

is called the nasal vestibule,

Question 53

the nasal vestibule,

Answer 53

is surrounded by cartilage

Question 54

the superior part of the nasal cavity is

Answer 54

surrounded by bone.

Question 55

When air enters the nostrils,

Answer 55

it passes first through the nasal vestibule

Question 56

the nasal vestibule is lined by

Answer 56

skin containing coarse hairs that filter out large dust particles.

Question 57

Three shelves are formed by projections of the

Answer 57

superior nasal conchae, middle nasal conchae, and inferior nasal conchae bones (KON-kē) extend out of each lateral wall of the nasal cavity.

Question 58

The conchae, almost reaching the nasal septum,

Answer 58

subdivide each side of the nasal cavity into a series of groovelike air passageways—the superior, middle, and inferior nasal meatuses

Question 59

Mucous membrane lines

Answer 59

the nasal cavity and its shelves

Question 60

The arrangement of conchae and meatuses

Answer 60

increases surface area in the internal nose and prevents dehydration by trapping water droplets during exhalation.

Question 61

As inhaled air whirls around the conchae and meatuses,

Answer 61

it is warmed by blood in the capillaries.

Question 62

Mucus secreted by the goblet cells in the nasal conchae and meatuses

Answer 62

moistens the air and traps dust particles.

Question 63

The cilia in the nasal conchae and meatuses

Answer 63

move the mucus and trapped dust particles toward the pharynx, at which point they can be swallowed or spit out, thus removing the particles from the respiratory tract.

Question 64

The olfactory sensory neurons, supporting epithelial cells, and basal epithelial cells lie

Answer 64

in the respiratory region, which is near the superior nasal conchae and adjacent septum.These cells make up the olfactory epithelium. It contains cilia but no goblet cells

Question 65

The pharynx (FAR-inks), or throat, is

Answer 65

a funnel-shaped tube about 13 cm (5 in.) long that starts at the choanae and extends to the level of the cricoid cartilage, the most inferior cartilage of the larynx (voice box)

Question 66

The pharynx lies

Answer 66

just posterior to the nasal and oral cavities, superior to the larynx, and just anterior to the cervical vertebrae.

Question 67

The pharynx´s wall is composed of

Answer 67

skeletal muscles and is lined with a mucous membrane.

Question 68

Relaxed skeletal muscles help keep the pharynx

Answer 68

patent

Question 69

Contraction of the skeletal muscles in the pharynx

Answer 69

assists in deglutition (swallowing).

Question 70

The pharynx functions as

Answer 70

a passageway for air and food, provides a resonating chamber for speech sounds, and houses the tonsils, which participate in immunological reactions against foreign invaders.

Question 71

The pharynx can be divided into three anatomical regions:

Answer 71

(1) nasopharynx, (2) oropharynx, and (3) laryngopharynx.

Question 72

The muscles of the entire pharynx are

Answer 72

arranged in two layers, an outer circular layer and an inner longitudinal layer.

Question 73

The superior portion of the pharynx, called the nasopharynx, lies

Answer 73

posterior to the nasal cavity and extends to the soft palate.

Question 74

The soft palate, which forms the posterior portion of the roof of the mouth, is

Answer 74

an arch-shaped muscular partition between the nasopharynx and oropharynx that is lined by mucous membrane.

Question 75

There are five openings in the wall of the soft palate:

Answer 75

two choanae, two openings that lead into the auditory (pharyngotympanic) tubes (commonly known as the eustachian tubes), and the opening into the oropharynx

Question 76

The posterior wall of the soft palate also contains

Answer 76

the pharyngeal tonsil (fa-RIN-je-al), or adenoid

Question 77

Through the choanae, the nasopharynx

Answer 77

receives air from the nasal cavity along with packages of dust-laden mucus.

Question 78

The nasopharynx is lined with

Answer 78

ciliated pseudostratified columnar epithelium, and the cilia move the mucus down toward the most inferior part of the nasopharynx.

Question 79

The nasopharynx also exchanges small amounts of air with

Answer 79

the auditory tubes to equalize air pressure between the tympanic cavity and the atmosphere.

Question 80

The intermediate portion of the pharynx, the oropharynx, lies

Answer 80

posterior to the oral cavity and extends from the soft palate inferiorly to the level of the upper border of the epiglottis.

Question 81

The oropharynx

Answer 81

has only one opening into it, the fauces (FAW-sēz = throat), the opening from the mouth.

Question 82

the oropharynx has both

Answer 82

respiratory and digestive functions, serving as a common passageway for air, food, and drink.

Question 83

Because the oropharynx is subject to abrasion by food particles,

Answer 83

it is lined with nonkeratinized stratified squamous epithelium.

Question 84

Two pairs of tonsils, are found in the oropharynx.

Answer 84

the palatine and lingual tonsils,

Question 85

The inferior portion of the pharynx, the laryngopharynx (la-RING-gō-far-ingks) begins

Answer 85

at the level of the hyoid bone.

Question 86

At its inferior end the laryngopharynx opens into

Answer 86

the esophagus (food tube) posteriorly and the larynx (voice box) anteriorly

Question 87

Like the oropharynx, the laryngopharynx is both

Answer 87

a respiratory and a digestive pathway and is lined by nonkeratinized stratified squamous epithelium.

Question 88

The larynx (LAR-ingks), or voice box, is

Answer 88

a short passageway that connects the laryngopharynx with the trachea.

Question 89

The larynx lies

Answer 89

in the midline of the neck anterior to the esophagus and the fourth through sixth cervical vertebrae (C4–C6).

Question 90

The wall of the larynx is composed of

Answer 90

nine pieces of cartilage

Question 91

Three of the pieces of cartilage that line the wall of the larynx ________________ and three occur _______________________

Answer 91

occur singly (thyroid cartilage, epiglottic cartilage, and cricoid cartilage),
in pairs (arytenoid, cuneiform, and corniculate cartilages).

Question 92

Of the paired cartilages, the arytenoid cartilages are

Answer 92

the most important because they influence changes in position and tension of the vocal folds (true vocal cords for speech).

Question 93

The extrinsic muscles of the larynx connect

Answer 93

the cartilages to other structures in the throat;

Question 94

the intrinsic muscles of the larynx

Answer 94

connect the cartilages to one another.

Question 95

The laryngeal cavity is

Answer 95

the space that extends from the entrance into the larynx down to the inferior border of the cricoid cartilage

Question 96

the laryngeal vestibule.

Answer 96

The portion of the laryngeal cavity above the vestibular folds (false vocal cords)

Question 97

the infraglottic cavity

Answer 97

The portion of the cavity of the larynx below the vocal folds is called

Question 98

The thyroid cartilage (laryngeal prominence or Adam’s apple) consists of

Answer 98

two fused plates of hyaline cartilage that form the anterior wall of the larynx and give it a triangular shape.

Question 99

the thyroid cartilage

Answer 99

is present in both males and females but is usually larger in males due to the influence of male sex hormones on its growth during puberty

Question 100

the thyrohyoid membrane.

Answer 100

The ligament that connects the thyroid cartilage to the hyoid bone

Question 101

The epiglottic cartilage (epi- = over; -glottic = tongue) is

Answer 101

a large, leaf-shaped piece of elastic cartilage

Question 102

The term epiglottis refers to

Answer 102

the epiglottic cartilage and its mucous membrane covering

Question 103

The “stem” of the epiglottis is

Answer 103

the tapered inferior portion that is attached to the internal surface of the thyroid cartilage.

Question 104

The broad superior “leaf” portion of the epiglottis is

Answer 104

unattached and is free to move up and down like a trap door.

Question 105

During swallowing,

Answer 105

the pharynx and larynx rise.

Question 106

Elevation of the pharynx

Answer 106

widens it to receive food or drink

Question 107

elevation of the larynx causes

Answer 107

the epiglottis to move down and form a lid over the glottis, closing it off.

Question 108

The glottis consists of

Answer 108

a pair of folds of mucous membrane, the vocal folds (true vocal cords) in the larynx, and the space between them called the rima glottidis (RĪ-ma GLOT-ti-dis).

Question 109

The closing of the larynx during swallowing

Answer 109

routes liquids and foods into the esophagus and keeps them out of the larynx and airways.

Question 110

When small particles of dust, smoke, food, or liquids pass into the larynx,

Answer 110

a cough reflex occurs, usually expelling the material.

Question 111

The cricoid cartilage (KRĪ-koyd = ringlike) is

Answer 111

a ring of hyaline cartilage that forms the inferior wall of the larynx.

Question 112

the cricoid cartilage is attached to

Answer 112

the first ring of cartilage of the trachea by the cricotracheal ligament (krī′-kō-TRĀ-kē-al).

Question 113

The thyroid cartilage is connected to

Answer 113

the cricoid cartilage by the cricothyroid ligament.

Question 114

The cricoid cartilage is the landmark for

Answer 114

making an emergency airway called a tracheotomy

Question 115

The paired arytenoid cartilages (ar′-i-TĒ-noyd = ladlelike) are

Answer 115

triangular pieces of mostly hyaline cartilage located at the posterior, superior border of the cricoid cartilage. They form synovial joints with the cricoid cartilage and have a wide range of mobility.

Question 116

The paired corniculate cartilages (kor-NIK-ū-lāt = shaped like a small horn),

Answer 116

horn-shaped pieces of elastic cartilage, are located at the apex of each arytenoid cartilage.

Question 117

The paired cuneiform cartilages (KŪ-nē-i-form = wedge-shaped),

Answer 117

club-shaped elastic cartilages anterior to the corniculate cartilages, support the vocal folds and lateral aspects of the epiglottis.

Question 118

The lining of the larynx superior to the vocal folds is

Answer 118

nonkeratinized stratified squamous epithelium.

Question 119

The lining of the larynx inferior to the vocal folds is

Answer 119

ciliated pseudostratified columnar epithelium consisting of ciliated columnar cells, goblet cells, and basal cells.

Question 120

The mucus produced by the goblet cells in the larynx

Answer 120

helps trap dust not removed in the upper passages

Question 121

The cilia in the upper respiratory tract

Answer 121

move mucus and trapped particles down toward the oropharynx;

Question 122

the cilia in the lower respiratory tract

Answer 122

move mucus and trapped particles up toward the laryngopharynx.

Question 123

The mucous membrane of the larynx forms

Answer 123

two pairs of folds

Question 124

the twopairs of folds formed by the mucous membrane of the larynx are

Answer 124

a superior pair called the vestibular folds (false vocal cords) and an inferior pair called the vocal folds (true vocal cords).

Question 125

The space between the vestibular folds is known as the

Answer 125

rima vestibuli.

Question 126

The laryngeal ventricle is a

Answer 126

lateral expansion of the middle portion of the laryngeal cavity inferior to the vestibular folds and superior to the vocal folds

Question 127

When the vestibular folds are brought together, they function in

Answer 127

holding the breath against pressure in the thoracic cavity, such as might occur when a person strains to lift a heavy object.

Question 128

The vocal folds are

Answer 128

the principal structures of voice production

Question 129

Deep to the mucous membrane of the vocal folds, which is nonkeratinized stratified squamous epithelium, are

Answer 129

bands of elastic ligaments stretched between the rigid cartilages of the larynx like the strings on a guitar.

Question 130

Intrinsic laryngeal muscles

Answer 130

attach to both the rigid cartilages and the vocal folds. When the muscles contract they move the cartilages, which pulls the elastic ligaments tight, and this stretches the vocal folds out into the airways so that the rima glottidis is narrowed.

Question 131

Contracting and relaxing the intrinsic laryngeal muscles

Answer 131

varies the tension in the vocal folds, much like loosening or tightening a guitar string.

Question 132

Air passing through the larynx vibrates the folds and produces sound (phonation) by

Answer 132

setting up sound waves in the column of air in the pharynx, nose, and mouth. The variation in the pitch of the sound is related to the tension in the vocal folds. The greater the pressure of air, the louder the sound produced by the vibrating vocal folds.

Question 133

When the intrinsic muscles of the larynx contract,

Answer 133

they pull on the arytenoid cartilages, which causes the cartilages to pivot and slide.

Question 134

Contraction of the posterior cricoarytenoid muscles

Answer 134

moves the vocal folds apart (abduction), thereby opening the rima glottidis

Question 135

contraction of the lateral cricoarytenoid muscles

Answer 135

moves the vocal folds together (adduction), thereby closing the rima glottidis

Question 136

Other intrinsic muscles can

Answer 136

elongate (and place tension on) or shorten (and relax) the vocal folds.

Question 137

The glottis consists of

Answer 137

a pair of folds of mucous membrane in the larynx (the vocal folds) and the space between them (the rima glottidis).

Question 138

Pitch is controlled by

Answer 138

the tension on the vocal folds. If they are pulled taut by the muscles, they vibrate more rapidly, and a higher pitch results. Decreasing the muscular tension on the vocal folds causes them to vibrate more slowly and produce lower-pitched sounds.

Question 139

Due to the influence of androgens (male sex hormones),

Answer 139

vocal folds are usually thicker and longer in males than in females, and therefore they vibrate more slowly. This is why a man’s voice generally has a lower range of pitch than that of a woman.

Question 140

Sound originates from

Answer 140

the vibration of the vocal folds, but other structures are necessary for converting the sound into recognizable speech.

Question 141

The pharynx, mouth, nasal cavity, and paranasal sinuses all act as

Answer 141

resonating chambers that give the voice its human and individual quality.

Question 142

We produce the vowel sounds by

Answer 142

constricting and relaxing the muscles in the wall of the pharynx.

Question 143

Muscles of the face, tongue, and lips

Answer 143

help us enunciate words.

Question 144

Whispering is accomplished by

Answer 144

closing all but the posterior portion of the rima glottidis. Because the vocal folds do not vibrate during whispering, there is no pitch to this form of speech.

Question 145

we can still produce intelligible speech while whispering by

Answer 145

changing the shape of the oral cavity as we enunciate. As the size of the oral cavity changes, its resonance qualities change, which imparts a vowel-like pitch to the air as it rushes toward the lips

Question 146

Laryngitis is

Answer 146

an inflammation of the larynx that is most often caused by a respiratory infection or irritants such as cigarette smoke.

Question 147

Cancer of the larynx is found

Answer 147

almost exclusively in individuals who smoke

Question 148

The trachea (TRĀ-kē-a = sturdy), or windpipe, is

Answer 148

a tubular passageway for air that is about 12 cm (5 in.) long and 2.5 cm (1 in.) in diameter.

Question 149

The trachea

Answer 149

is located anterior to the esophagus (Figure 23.7) and extends from the larynx to the superior border of the fifth thoracic vertebra (T5), where it divides into right and left primary bronchi

Question 150

The trachea is located

Answer 150

anterior to the esophagus and extends from the larynx to the superior border of the fifth thoracic vertebra.

Question 151

The bronchial tree consists of .

Answer 151

macroscopic airways that begin at the trachea and continue through the terminal bronchioles

Question 152

The layers of the tracheal wall, from deep to superficial, are

Answer 152

the (1) respiratory mucosa, (2) submucosa, (3) hyaline cartilage, and (4) adventitial layer (composed of areolar connective tissue).

Question 153

The respiratory mucosa of the trachea consists of

Answer 153

an epithelial layer of ciliated pseudostratified columnar epithelium and an underlying layer of lamina propria that contains elastic and reticular fibers.

Question 154

The respiratory mucosa of the trachea

Answer 154

provides the same protection against dust as the membrane lining the nasal cavity and larynx.

Question 155

The submucosa consists of

Answer 155

areolar connective tissue that contains seromucous glands and their ducts.

Question 156

The 16–20 incomplete, horizontal rings of hyaline cartilage on the trachea

Answer 156

resemble the letter C, are stacked one above another, and are connected by dense connective tissue.They may be felt through the skin inferior to the larynx.

Question 157

The open part of each C-shaped cartilage ring

Answer 157

faces posteriorly toward the esophagus (Figure 23.7) and is spanned by the membranous wall of the trachea.

Question 158

Within themembranous wall of the trachea are

Answer 158

transverse smooth muscle fibers, called the trachealis muscle (trā-kē-Ā-lis), and elastic connective tissue that allow the diameter of the trachea to change subtly during inhalation and exhalation, which is important in maintaining efficient airflow.

Question 159

The solid C-shaped cartilage rings provide

Answer 159

a semirigid support to maintain patency so that the tracheal wall does not collapse inward (especially during inhalation) and obstruct the air passageway.

Question 160

The adventitial layer of the trachea consists of

Answer 160

areolar connective tissue that joins the trachea to surrounding tissues.

Question 161

tracheostomy

Answer 161

a surgical procedure in which a skin incision is followed by a short longitudinal incision into the trachea below the cricoid cartilage. Then, an endotracheal (within the trachea) tube (en-dō- TRĀK- ē-al) is placed through the opening to provide an airway when the usual route for breathing is obstructed or impaired and to remove secretions from the lungs

Question 162

endotracheal intubation, or simply intubation.

Answer 162

In this procedure, also done in a hospital setting under anesthesia, an endotracheal tube is advanced through the mouth (or sometimes the nose), pharynx, and larynx into the trachea

Question 163

A mechanical ventilator or simply a ventilator, is

Answer 163

a machine that is used to support ventilation (breathing). It is a form of life support

Question 164

At the superior border of the fifth thoracic vertebra,

Answer 164

the trachea divides into a right main (primary) bronchus (BRONG-kus = windpipe), which goes into the right lung, and a left main (primary) bronchus, which goes into the left lung

Question 165

The right main bronchus is

Answer 165

more vertical, shorter, and wider than the left

Question 166

an aspirated object is more likely to enter and lodge in the

Answer 166

right main bronchus than the left

Question 167

Like the trachea, the main bronchi (BRONG-kī) contain

Answer 167

incomplete rings of cartilage and are lined by ciliated pseudostratified columnar epithelium.

Question 168

At the point where the trachea divides into right and left main bronchi

Answer 168

an internal ridge called the carina (ka-RĪ-na = keel of a boat) is formed by a posterior and somewhat inferior projection of the last tracheal cartilage.

Question 169

The mucous membrane of the carina is

Answer 169

one of the most sensitive areas of the entire larynx and trachea for triggering a cough reflex.

Question 170

Widening and distortion of the carina is a serious sign because

Answer 170

it usually indicates a carcinoma of the lymph nodes around the region where the trachea divides.

Question 171

On entering the lungs, the main bronchi

Answer 171

divide to form smaller bronchi—the lobar (secondary) bronchi, one for each lobe of the lung.

Question 172

The right lung has

Answer 172

three lobes; the left lung has two.)

Question 173

The lobar bronchi continue to

Answer 173

branch, forming still smaller bronchi, called segmental (tertiary) bronchi (TER-shē-e-rē), that supply the specific bronchopulmonary segments within the lobes.

Question 174

There are _________________ segmental bronchi in the right lung and __________ segmental bronchi in the left lung.

Answer 174

13
8

Question 175

The segmental bronchi

Answer 175

divide into bronchioles

Question 176

Bronchioles

Answer 176

branch repeatedly, and the smallest ones branch into even smaller tubes called terminal bronchioles.

Question 177

terminal bronchioles contain

Answer 177

exocrine bronchiolar (Clara) cells, which are nonciliated columnar cells, interspersed among ciliated simple columnar cells.

Question 178

The exocrine bronchiolar cells may

Answer 178

protect against harmful effects of inhaled toxins and carcinogens, produce surfactant (discussed shortly), and function as stem cells, which give rise to various cells of the epithelium

Question 179

The terminal bronchioles represent

Answer 179

the end of the conducting zone of the respiratory system.

Question 180

The extensive branching from the trachea through the terminal bronchioles

Answer 180

resembles an inverted tree and is commonly referred to as the bronchial tree.

Question 181

Beyond the terminal bronchioles of the bronchial tree,

Answer 181

the branches become microscopic. These branches are called the respiratory bronchioles and alveolar ducts,

Question 182

The respiratory passages from the trachea to the alveolar ducts contain

Answer 182

about 23 generations of branching; branching from the trachea into main bronchi is called first-generation branching, that from main bronchi into lobar bronchi is called second-generation branching, and so on down to the alveolar ducts

Question 183

How does the epithelium of the bronchial tree change as branching becomes more extensive

Answer 183

The mucous membrane in the bronchial tree changes from ciliated pseudostratified columnar epithelium in the main bronchi, lobar bronchi, and segmental bronchi to ciliated simple columnar epithelium with some goblet cells in larger bronchioles, to mostly ciliated simple cuboidal epithelium with no goblet cells in smaller bronchioles, to mostly nonciliated simple cuboidal epithelium in terminal bronchioles.

Question 184

ciliated epithelium of the respiratory membrane removes inhaled particles in two ways

Answer 184

1 mucus produced by goblet cells traps the particles, and the cilia move the mucus and trapped particles toward the pharynx for removal.
2 In regions where nonciliated simple cuboidal epithelium is present, inhaled particles are removed by macrophages.

Question 185

Describe the structural changes in cartilage as branching becomes more extensive in the bronchial tree

Answer 185

Plates of cartilage gradually replace the incomplete rings of cartilage in main bronchi and finally disappear in the distal bronchioles.

Question 186

Describe the relationship between cartilage and smooth muscle as branching becomes more extensive in the bronchial tree

Answer 186

As the amount of cartilage decreases, the amount of smooth muscle increases. Smooth muscle encircles the epithelial-lined lumen in spiral bands and helps maintain patency. However, because there is no supporting cartilage, muscle spasms can close off the airways.

Question 187

During exercise, activity in the sympathetic part of the autonomic nervous system (ANS)

Answer 187

increases and the suprarenal medulla releases the hormones epinephrine and norepinephrine; both of these events cause relaxation of smooth muscle in the bronchioles, which dilates the airways.Because air reaches the pulmonary alveoli more quickly, lung ventilation improves.

Question 188

The parasympathetic part of the ANS and mediators of allergic reactions such as histamine

Answer 188

cause contraction of bronchiolar smooth muscle, which results in constriction of distal bronchioles.

Question 189

A pulmonologist (pul-mō-NOL-ō-gist; pulmo- = lung) is

Answer 189

a specialist in the diagnosis and treatment of lung diseases.

Question 190

The lungs (= lightweights, because they float) are

Answer 190

paired cone-shaped organs in the thoracic cavity

Question 191

The lungs are separated from each other by

Answer 191

the heart and other structures of the mediastinum, which divides the thoracic cavity into two anatomically distinct chambers.

Question 192

if trauma causes one lung to collapse,

Answer 192

the other may remain expanded.

Question 193

Each lung is enclosed and protected by

Answer 193

a double-layered serous membrane called the pleural membrane (PLOOR-al; pleur- = side) or pleura

Question 194

The superficial layer, called the parietal pleura,

Answer 194

lines the wall of the thoracic cavity

Question 195

the deep layer, the visceral pleura,

Answer 195

covers the lungs themselves

Question 196

Between the visceral and parietal pleurae is

Answer 196

a small space, the pleural cavity, which contains a small amount of lubricating fluid secreted by the membranes.

Question 197

What is the function of pleural fluid

Answer 197

pleural fluid reduces friction between the membranes, allowing them to slide easily over one another during breathing. Pleural fluid also causes the two membranes to adhere to one another just as a film of water causes two glass microscope slides to stick together, a phenomenon called surface tension.

Question 198

Separate pleural cavities

Answer 198

surround the left and right lungs.

Question 199

Inflammation of the pleural membrane, called pleurisy or pleuritis,

Answer 199

may in its early stages cause pain due to friction between the parietal and visceral layers of the pleura. If the inflammation persists, excess fluid accumulates in the pleural space, a condition known as pleural effusion.

Question 200

In certain conditions, the pleural cavities may fill with

Answer 200

air (pneumothorax; noo′-mō-THOR-aks; pneumo- = air or breath), blood (hemothorax), or pus.

Question 201

collapse of a part of a lung, or rarely an entire lung, is called

Answer 201

atelectasis

Question 202

The lungs extend from

Answer 202

the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly

Question 203

The broad inferior portion of the lung,

Answer 203

the base, is concave and fits over the convex area of the diaphragm.

Question 204

The narrow superior portion of the lung is the

Answer 204

apex

Question 205

The surface of the lung lying against the ribs,

Answer 205

the costal surface, matches the rounded curvature of the ribs.

Question 206

The mediastinal (medial) surface of each lung contains a region,

Answer 206

the hilum, through which bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit These structures are held together by the pleura and connective tissue and constitute the root of the lung.

Question 207

Medially, the left lung also contains a concavity,

Answer 207

the cardiac notch, in which the apex of the heart lies.

Question 208

Due to the space occupied by the heart,

Answer 208

the left lung is about 10% smaller than the right lung.

Question 209

Although the right lung is thicker and broader,

Answer 209

it is also somewhat shorter than the left lung because the diaphragm is higher on the right side, accommodating the liver that lies inferior to it.

Question 210

The oblique fissure

Answer 210

divides the left lung into two lobes.

Question 211

The oblique and horizontal fissures

Answer 211

divide the right lung into three lobes.

Question 212

The apex of the lungs lies

Answer 212

superior to the medial third of the clavicles, and this is the only area that can be palpated.

Question 213

The anterior, lateral, and posterior surfaces of the lungs

Answer 213

lie against the ribs.

Question 214

The base of the lungs extends from

Answer 214

the sixth costal cartilage anteriorly to the spinous process of the tenth thoracic vertebra posteriorly.

Question 215

The pleura extends

Answer 215

about 5 cm (2 in.) below the base from the sixth costal cartilage anteriorly to the twelfth rib posteriorly. Thus, the lungs do not completely fill the pleural cavity in this area.

Question 216

Removal of excessive fluid in the pleural cavity can be accomplished without injuring lung tissue by

Answer 216

inserting a needle anteriorly through the seventh intercostal space, a procedure called thoracentesis (thor′-a-sen-TĒ-sis; -centesis = puncture).The needle is passed along the superior border of the lower rib to avoid damage to the intercostal nerves and blood vessels. Inferior to the seventh intercostal space there is danger of penetrating the diaphragm.

Question 217

One or two fissures divide each lung

Answer 217

into sections called lobes

Question 218

Both lungs have

Answer 218

an oblique fissure, which extends inferiorly and anteriorly;

Question 219

the right lung also has

Answer 219

a horizontal fissure

Question 220

The oblique fissure in the left lung

Answer 220

separates the superior lobe from the inferior lobe.

Question 221

In the right lung, the superior part of the oblique fissure

Answer 221

separates the superior lobe from the inferior lobe;

Question 222

in the right lung the inferior part of the oblique fissure

Answer 222

separates the inferior lobe from the middle lobe, which is bordered superiorly by the horizontal fissure.

Question 223

Each lobe receives

Answer 223

its own lobar bronchus.

Question 224

the right main bronchus gives rise to three lobar bronchi called the superior, middle, and inferior lobar bronchi,

Answer 224

three lobar bronchi called the superior, middle, and inferior lobar bronchi,

Question 225

the left main bronchus gives rise to

Answer 225

two lobar bronchi called the superior and inferior lobar bronchi

Question 226

Within the lung, the lobar bronchi give rise to

Answer 226

the segmental bronchi, which are constant in both origin and distribution

Question 227

there are ________________segmental bronchi in each lung

Answer 227

10

Question 228

bronchopulmonary segment

Answer 228

The portion of lung tissue that each segmental bronchus supplies

Question 229

Each bronchopulmonary segment of the lungs

Answer 229

has many small compartments called lobules

Question 230

each lobule

Answer 230

is wrapped in elastic connective tissue and contains a lymphatic vessel, an arteriole, a venule, and a branch from a terminal bronchiole

Question 231

Terminal bronchioles in a lobule subdivide into

Answer 231

microscopic branches called respiratory bronchioles

Question 232

respiratory bronchioles

Answer 232

have pulmonary alveoli (described shortly) budding from their walls

Question 233

Pulmonary alveoli participate in

Answer 233

gas exchange

Question 234

respiratory bronchioles begin

Answer 234

the respiratory zone of the respiratory system.

Question 235

As the respiratory bronchioles penetrate more deeply into the lungs, the epithelial lining changes

Answer 235

from simple cuboidal to simple squamous

Question 236

Respiratory bronchioles in turn subdivide into

Answer 236

several (2–11) alveolar ducts (al-vē-Ō-lar), which consist of simple squamous epithelium.

Question 237

The terminal dilation of an alveolar duct is called

Answer 237

an alveolar saccule or alveolar sac and is analogous to a cluster of grapes.

Question 238

Each alveolar saccule is composed of

Answer 238

outpouchings called pulmonary alveoli (al-vē-Ō-Iī), analogous to individual grapes

Question 239

There are about _______________at the end of each alveolar duct and each alveolar saccule contains ___________________

Answer 239

100 alveolar saccules
about 20–30 pulmonary alveoli,

Question 240

The wall of each pulmonary alveolus (singular) consists of

Answer 240

two types of alveolar epithelial cells

Question 241

What is the name and function of the most numerous aveolar cell

Answer 241

The more numerous (about 95%) pneumocyte type I (type I alveolar cell) are simple squamous epithelial cells that form a nearly continuous lining of the pulmonary alveolar wall

Question 242

Describe Pneumocyte type II

Answer 242

(type II alveolar cell), also called septal cells, are fewer in number and are found between pneumocytes type I

Question 243

The thin wall of pneumocytes type I

Answer 243

are the main sites of gas exchange.

Question 244

Pneumocytes type I are

Answer 244

rounded or cuboidal epithelial cells with free surfaces containing microvilli, secrete pulmonary alveolar fluid, which keeps the surface between the cells and the air moist.

Question 245

Included in the pulmonary alveolar fluid is

Answer 245

surfactant (sur-FAK-tant), a complex mixture of phospholipids and lipoproteins

Question 246

Surfactant function

Answer 246

lowers the surface tension of pulmonary alveolar fluid, which reduces the tendency of pulmonary alveoli to collapse and thus maintains their patency (described later).

Question 247

An alveolar saccule is

Answer 247

the terminal dilation of an alveolar duct and is composed of pulmonary alveoli.

Question 248

Also present in the aveolar wall is

Answer 248

aveolar macrophages and fibroblasts

Question 249

What is the function of aveolar macrophages

Answer 249

phagocytes that remove fine dust particles and other debris from the pulmonary alveolar spaces

Question 250

What is the function of fibroblasts in the aveolar wall

Answer 250

produce reticular and elastic fibers.

Question 251

Underlying the layer of pneumocytes type I is

Answer 251

an elastic basement membrane

Question 252

On the outer surface of the pulmonary alveoli,

Answer 252

the lobule’s arteriole and venule disperse into a network of blood capillaries (see Figure 23.11a) that consist of a single layer of endothelial cells and basement membrane.

Question 253

The exchange of O2 and CO2 between the air spaces in the lungs and the blood takes place

Answer 253

by diffusion across the pulmonary alveolar and capillary walls, which together form the respiratory membrane

Question 254

Extending from the pulmonary alveolar air space to blood plasma,

Answer 254

the respiratory membrane consists of four layers

Question 255

Describe the four layers of the respiratory membrane

Answer 255

A layer of pneumocytes type I and type II and associated alveolar macrophages that constitutes the alveolar wall
An epithelial basement membrane underlying the pulmonary alveolar wall
A capillary basement membrane that is often fused to the epithelial basement membrane
The capillary endothelium

Question 256

Despite having several layers,

Answer 256

the respiratory membrane is very thin

Question 257

It has been estimated that both lungs contain

Answer 257

300–500 million pulmonary alveoli, providing an immense surface area of about 75 m2 (807 ft2)—about the size of a racquetball court or slightly larger—for gas exchange.

Question 258

The hundreds of millions of pulmonary alveoli account for

Answer 258

the spongy texture of the lungs.

Question 259

The lungs receive blood via

Answer 259

two sets of arteries: pulmonary arteries and bronchial arteries

Question 260

Deoxygenated blood

Answer 260

passes through the pulmonary trunk, which divides into a left pulmonary artery that enters the left lung and a right pulmonary artery that enters the right lung.

Question 261

(The pulmonary arteries are the only arteries in the body

Answer 261

that carry deoxygenated blood.)

Question 262

Return of the oxygenated blood to the heart occurs by way of

Answer 262

the four pulmonary veins, which drain into the left atrium

Question 263

A unique feature of pulmonary blood vessels is

Answer 263

their constriction in response to localized hypoxia (low O2 level).

Question 264

In all body tissues besides the pulmonary blood vessels,

Answer 264

hypoxia causes dilation of blood vessels to increase blood flow

Question 265

In the lungs in response to hypoxia

Answer 265

vasoconstriction diverts pulmonary blood from poorly ventilated areas of the lungs to well-ventilated regions for more efficient gas exchange.This phenomenon is known as ventilation–perfusion coupling (per-FYU-zhun) because the perfusion (blood flow) to each area of the lungs matches the extent of ventilation (airflow) to alveoli in that area.

Question 266

Bronchial arteries, which branch from the aorta,

Answer 266

deliver oxygenated blood to the lungs This blood mainly perfuses the muscular walls of the bronchi and bronchioles.

Question 267

Connections do exist between

Answer 267

branches of the bronchial arteries and branches of the pulmonary arteries, however; most blood returns to the heart via pulmonary veins

Question 268

Some blood drains into

Answer 268

bronchial veins, branches of the azygos system, and returns to the heart via the superior vena cava.

Question 269

coryza (kō-RĪ-za),

Answer 269

the common cold

Question 270

List the structures dedicated to maintaining the patency of the respiratory system

Answer 270

the bony and cartilaginous frameworks of the nose, skeletal muscles of the pharynx, cartilages of the larynx, C-shaped rings of cartilage in the trachea and bronchi, smooth muscle in the bronchioles, and surfactant in the pulmonary alveoli.

Question 271

Unfortunately, there are also factors that can compromise patency. These include

Answer 271

crushing injuries to bone and cartilage, a deviated nasal septum, nasal polyps, inflammation of mucous membranes, spasms of smooth muscle, and a deficiency of surfactant.

Question 272

List the structures of the respiratory system that are lined by nonkeratinized stratified squamous epithelium

Answer 272

Nasal vestbule
oropharynx
laryngopharynx
larynx (above vocal folds)

Question 273

List the structures of the respiratory system that are lined by ciliated pseudostratified columnar epithelium

Answer 273

Respiratoey region of the nose
nasopharynx
Larynx below the vocal folds
trachea
main bronchi
Lobar bronchi
segmental bronchi

Question 274

The olfactory region of the nose is lined by

Answer 274

Olfactory epithelium (olfactory sensory neurons)

Question 275

Which respiratory system structures are lined by ciliated simple columnar epithelium

Answer 275

Larger bronchioles
smaller bronchioles

Question 276

What type of epithelium lines the terminal bronchioles

Answer 276

nonciliated simple columnar

Question 277

What type of epithelium lines the respiratory bronchioles

Answer 277

simple cuboidal to simple squamous

Question 278

Which respiratory system structures are lined by simple squamous epithelium

Answer 278

alveolar ducts
pulmonary alveoli

Question 279

List all of the respiratory system structures that contain goblet cells

Answer 279

Respiratory region of the nose
nasopharynx
larynx (below vocal folds)
trachea
main bronchi
lobar bronchi
segmental bronchi
larger bronchioles

Question 280

what are the only gas exchange structures in the respiratory system

Answer 280

respiratory bronchioles
alveolar ducts
pulmonary alveoli

Question 281

Pulmonary ventilation, or breathing, is

Answer 281

the flow of air into and out of the lungs.

Question 282

In pulmonary ventilation,

Answer 282

air flows between the atmosphere and the pulmonary alveoli of the lungs because of alternating pressure differences created by contraction and relaxation of respiratory muscles.

Question 283

The rate of airflow and the amount of effort needed for breathing are also influenced by

Answer 283

alveolar surface tension, compliance of the lungs, and airway resistance.

Question 284

Air moves into the pulmonary alveoli of the lungs when

Answer 284

the air pressure inside the lungs is less than the air pressure in the atmosphere

Question 285

Air moves out of the pulmonary alveoli of the lungs when

Answer 285

the air pressure inside the lungs is greater than the air pressure in the atmosphere.

Question 286

Breathing in is called

Answer 286

inhalation (inspiration).

Question 287

Just before each inhalation,

Answer 287

the air pressure inside the lungs is equal to the air pressure of the atmosphere,

Question 288

For air to flow into the lungs,

Answer 288

the pressure inside the pulmonary alveoli must become lower than the atmospheric pressure. This condition is achieved by increasing the size of the lungs.

Question 289

The pressure of a gas in a closed container is

Answer 289

inversely proportional to the volume of the container.

Question 290

if the size of a closed container is increased,

Answer 290

the pressure of the gas inside the container decreases, and that if the size of the container is decreased, then the pressure inside it increases.

Question 291

The inverse relationship between volume and pressure, is called

Answer 291

Boyle’s law

Question 292

Differences in pressure caused by changes in lung volume

Answer 292

force air into our lungs when we inhale and out when we exhale

Question 293

For inhalation to occur,

Answer 293

the lungs must expand, which increases lung volume and thus decreases the pressure in the lungs to below atmospheric pressure

Question 294

The first step in expanding the lungs during normal quiet inhalation involves

Answer 294

contraction of the main muscle of inhalation, the diaphragm, with resistance from external intercostals

Question 295

The most important muscle of inhalation is

Answer 295

the diaphragm, the dome-shaped skeletal muscle that forms the floor of the thoracic cavity

Question 296

the diaphragm

Answer 296

is innervated by fibers of the phrenic nerves, which emerge from the spinal cord at cervical levels 3, 4, and 5.

Question 297

Contraction of the diaphragm causes

Answer 297

the diaphragm to flatten, lowering its dome.This increases the vertical diameter of the thoracic cavity

Question 298

During normal quiet inhalation,

Answer 298

the diaphragm descends about 1 cm (0.4 in.), producing a pressure difference of 1–3 mmHg and the inhalation of about 500 mL of air.

Question 299

In strenuous breathing,

Answer 299

the diaphragm may descend 10 cm (4 in.), which produces a pressure difference of 100 mmHg and the inhalation of 2–3 liters of air.

Question 300

Contraction of the diaphragm is responsible for

Answer 300

about 75% of the air that enters the lungs during quiet breathing.

Question 301

The second most important muscles of inhalation are

Answer 301

the external intercostals. When these muscles contract, they elevate the ribs. As a result, there is an increase in the anteroposterior and lateral diameters of the chest cavity.

Question 302

Contraction of the external intercostals is responsible for

Answer 302

about 25% of the air that enters the lungs during normal quiet breathing.

Question 303

During normal, quiet inhalation,

Answer 303

the diaphragm and external intercostals contract, the lungs expand, and air moves into the pulmonary alveoli of the lungs

Question 304

during normal, quiet exhalation,

Answer 304

the diaphragm and external intercostals relax and the lungs recoil, forcing air out of the pulmonary alveoli of the lungs

Question 305

Intrapleural pressure is

Answer 305

the pressure within the pleural cavity.

Question 306

Intrapleural pressure is always

Answer 306

a negative pressure (lower than atmospheric pressure), ranging from 754–756 mmHg during normal quiet breathing.

Question 307

since the pleural cavity has a negative pressure,

Answer 307

it essentially functions as a vacuum. The suction of this vacuum attaches the visceral pleura to the chest wall. Thus, if the thoracic cavity increases in size, the lungs also expand; if the thoracic cavity decreases in size, the lungs recoil (become smaller).

Question 308

Just before inhalation, intrapleural pressure is

Answer 308

about 4 mmHg less than atmospheric pressure, or about 756 mmHg at an atmospheric pressure of 760 mmHg

Question 309

As the diaphragm and external intercostals contract and the overall size of the thoracic cavity increases,

Answer 309

the volume of the pleural cavity also increases, which causes intrapleural pressure to decrease to about 754 mmHg.

Question 310

As the thoracic cavity expands, the parietal pleura lining the cavity

Answer 310

is pulled outward in all directions, and the visceral pleura and lungs and pulled along with it.

Question 311

As the volume of the lungs increases the pressure of air within the pulmonary alveoli of the lungs, called the alveolar (intrapulmonic) pressure,

Answer 311

drops from 760 to 758 mmHg. A pressure difference is thus established between the atmosphere and the pulmonary alveoli. since air always flows from a region of higher pressure to a region of lower pressure, inhalation takes place. Air continues to flow into the lungs as long as a pressure difference exists

Question 312

Although the lungs enlarge in all directions during inhalation,

Answer 312

most of the increase in volume appears to be due to the lengthening and expansion of the alveolar ducts and the increase in size of the openings into the alveoli.

Question 313

During deep, forceful inhalations,

Answer 313

accessory muscles of inspiration also participate in increasing the size of the thoracic cavity

Question 314

accessory muscles of inhalation are so named because

Answer 314

they make little, if any, contribution during normal quiet inhalation, but during exercise or forced breathing they may contract vigorously.

Question 315

The accessory muscles of inhalation include

Answer 315

the sternocleidomastoid muscles, which elevate the sternum; the scalene muscles, which elevate the first two ribs; and the pectoralis minor muscles, which elevate the third through fifth ribs

Question 316

since both normal quiet inhalation and inhalation during exercise or forced breathing involve muscular contraction,

Answer 316

the process of inhalation is said to be active.

Question 317

Breathing out, called exhalation (expiration), is also due to

Answer 317

a pressure gradient, but in this case the gradient is in the opposite direction: The pressure in the lungs is greater than the pressure of the atmosphere.

Question 318

Normal exhalation during quiet breathing, unlike inhalation

Answer 318

, is a passive process because no muscular contractions are involved. Instead, exhalation results from elastic recoil of the chest wall and lungs, both of which have a natural tendency to spring back after they have been stretched.

Question 319

Two inwardly directed forces contribute to elastic recoil:

Answer 319

1) the recoil of elastic fibers that were stretched during inhalation and (2) the inward pull of surface tension due to the film of intrapleural fluid between the visceral and parietal pleurae.

Question 320

Exhalation starts

Answer 320

when the inspiratory muscles relax.

Question 321

As the diaphragm relaxes,

Answer 321

its dome moves superiorly owing to its elasticity.

Question 322

As the external intercostals relax,

Answer 322

the ribs are depressed. These movements decrease the vertical, lateral, and anteroposterior diameters of the thoracic cavity, which decreases lung volume.

Question 323

As lung volume decreases

Answer 323

the alveolar pressure increases to about 762 mmHg. Air then flows from the area of higher pressure in the pulmonary alveoli to the area of lower pressure in the atmosphere

Question 324

Exhalation becomes active

Answer 324

only during forceful breathing, as occurs while playing a wind instrument or during exercise.

Question 325

During active exhalation,

Answer 325

muscles of exhalation—the abdominal and internal intercostals (see Figure 23.14a)—contract, which increases pressure in the abdominal region and thorax.

Question 326

Contraction of the abdominal muscles

Answer 326

moves the inferior ribs downward and compresses the abdominal viscera, thereby forcing the diaphragm superiorly.

Question 327

Contraction of the internal intercostals, which extend inferiorly and posteriorly between adjacent ribs

Answer 327

, pulls the ribs inferiorly

Question 328

Although intrapleural pressure is always less than alveolar pressure,

Answer 328

it may briefly exceed atmospheric pressure during a forceful exhalation, such as during a cough.

Question 329

three other factors affect the rate of airflow and the ease of pulmonary ventilation:

Answer 329

surface tension of the alveolar fluid, compliance of the lungs, and airway resistance.

Question 330

a thin layer of alveolar fluid coats the luminal surface of pulmonary alveoli and

Answer 330

exerts a force known as surface tension.

Question 331

Surface tension arises

Answer 331

at all air–water interfaces because the polar water molecules are more strongly attracted to each other than they are to gas molecules in the air

Question 332

When liquid surrounds a sphere of air, as in a pulmonary alveolus or a soap bubble,

Answer 332

surface tension produces an inwardly directed force.

Question 333

In the lungs, surface tension causes

Answer 333

the pulmonary alveoli to assume the smallest possible diameter.

Question 334

During breathing, surface tension must be

Answer 334

overcome to expand the lungs during each inhalation.

Question 335

Surface tension also accounts for

Answer 335

two-thirds of lung elastic recoil, which decreases the size of pulmonary alveoli during exhalation.

Question 336

The surfactant (a mixture of phospholipids and lipoproteins) present in alveolar fluid

Answer 336

reduces its surface tension below the surface tension of pure water.

Question 337

A deficiency of surfactant in premature infants causes respiratory distress syndrome, in which

Answer 337

the surface tension of pulmonary alveolar fluid is greatly increased, so that many pulmonary alveoli collapse at the end of each exhalation. Great effort is then needed at the next inhalation to reopen the collapsed pulmonary alveoli.

Question 338

Respiratory distress syndrome (RDS) is

Answer 338

a breathing disorder of premature newborns in which the pulmonary alveoli do not remain open due to a lack of surfactant.

Question 339

Compliance refers to

Answer 339

how much effort is required to stretch the lungs and chest wall.

Question 340

High compliance means that

Answer 340

the lungs and chest wall expand easily; low compliance means that they resist expansion.

Question 341

In the lungs, compliance is related to two principal factors:

Answer 341

elasticity and surface tension.

Question 342

The lungs normally have

Answer 342

high compliance and expand easily because elastic fibers in lung tissue are easily stretched and surfactant in alveolar fluid reduces surface tension.

Question 343

Decreased compliance is a common feature in pulmonary conditions that

Answer 343

(1) scar lung tissue (for example, tuberculosis), (2) cause lung tissue to become filled with fluid (pulmonary edema), (3) produce a deficiency in surfactant, or (4) impede lung expansion in any way

Question 344

Increased lung compliance occurs in

Answer 344

emphysema due to destruction of elastic fibers in alveolar walls

Question 345

Airflow equals

Answer 345

the pressure difference between the pulmonary alveoli and the atmosphere divided by the resistance.

Question 346

The walls of the airways, especially the bronchioles,

Answer 346

offer some resistance to the normal flow of air into and out of the lungs

Question 347

As the lungs expand during inhalation,

Answer 347

the bronchioles enlarge because their walls are pulled outward in all directions. Larger-diameter airways have decreased resistance

Question 348

Airway resistance increases during

Answer 348

exhalation as the diameter of bronchioles decreases.

Question 349

Airway diameter is also regulated by

Answer 349

the degree of contraction or relaxation of smooth muscle in the walls of the airways

Question 350

Signals from the sympathetic division of the autonomic nervous system (ANS) cause

Answer 350

relaxation of bronchiolar smooth muscle (bronchodilation), which results in decreased resistance.

Question 351

Signals from the parasympathetic part of the ANS cause

Answer 351

contraction of bronchiolar smooth muscle (bronchoconstriction) resulting in increased resistance.

Question 352

Any condition that narrows or obstructs the airways

Answer 352

increases resistance, so that more pressure is required to maintain the same airflow.

Question 353

The hallmark of asthma or chronic obstructive pulmonary disease (COPD)—emphysema or chronic bronchitis—is

Answer 353

increased airway resistance due to obstruction or collapse of airways.

Question 354

The term for the normal pattern of quiet breathing is

Answer 354

eupnea (ūp-NĒ-a; eu- = good, easy, or normal; -pnea = breath). Eupnea can consist of shallow, deep, or combined shallow and deep breathing.

Question 355

A pattern of shallow (chest) breathing, called costal breathing, consists of

Answer 355

an upward and outward movement of the chest due to contraction of the external intercostal muscles.

Question 356

A pattern of deep (abdominal) breathing, called diaphragmatic breathing (dī′-a-frag-MAT-ik), consists of

Answer 356

the outward movement of the abdomen due to the contraction and descent of the diaphragm.

Question 357

Coughing.

Answer 357

A long-drawn and deep inhalation followed by a complete closure of the rima glottidis, which results in a strong exhalation that suddenly pushes the rima glottidis open and sends a blast of air through the upper respiratory passages. Stimulus for this reflex act may be a foreign body lodged in the larynx, trachea, or epiglottis

Question 358

Sneezing

Answer 358

Spasmodic contraction of muscles of exhalation that forcefully expels air through the nose and mouth. Stimulus may be an irritation of the nasal mucosa

Question 359

Sighing

Answer 359

A long-drawn and deep inhalation immediately followed by a shorter but forceful exhalation.

Question 360

Yawning

Answer 360

A deep inhalation through the widely opened mouth producing an exaggerated depression of the mandible. It may be stimulated by drowsiness or someone else’s yawning, but the precise cause is unknown.

Question 361

Sobbing

Answer 361

A series of convulsive inhalations followed by a single prolonged exhalation. The rima glottidis closes earlier than normal after each inhalation so only a little air enters the lungs with each inhalation.

Question 362

Crying

Answer 362

An inhalation followed by many short convulsive exhalations, during which the rima glottidis remains open and the vocal folds vibrate; accompanied by characteristic facial expressions and tears.

Question 363

Laughing

Answer 363

The same basic movements as crying, but the rhythm of the movements and the facial expressions usually differ from those of crying. Laughing and crying are sometimes indistinguishable.

Question 364

Hiccupping

Answer 364

Spasmodic contraction of the diaphragm followed by a spasmodic closure of the rima glottidis, which produces a sharp sound on inhalation. Stimulus is usually irritation of the sensory nerve endings of the digestive canal.

Question 365

Valsalva (val-SAL-va) maneuver

Answer 365

Forced exhalation against a closed rima glottidis as may occur during periods of straining while defecating.

Question 366

Pressurizing the middle ear

Answer 366

The nose and mouth are held closed and air from the lungs is forced through the auditory meatus into the middle ear. Employed by those snorkeling or scuba diving during descent to equalize the pressure of the middle ear with that of the external environment.

Question 367

The different amounts of air moving into and out of the lungs can be classified into two types:

Answer 367

(1) lung volumes, which can be measured directly by use of a spirometer (described shortly) and (2) lung capacities, which are combinations of different lung volumes.

Question 368

The apparatus used to measure volumes and capacities is called a spirometer

Answer 368

spirometer

Question 369

in a spirogram.

Answer 369

Inhalation is recorded as an upward deflection and exhalation is recorded as a downward deflection (Figure 23.16).

Question 370

In general, lung volumes and capacities are larger in

Answer 370

males, taller individuals, younger adults, people who live at higher altitudes, and those who are not obese.

Question 371

Lung capacities are

Answer 371

combinations of various lung volumes.

Question 372

While at rest, a healthy adult averages

Answer 372

12 breaths a minute, with each inhalation and exhalation moving about 500 mL of air into and out of the lungs

Question 373

The volume of one breath is called the

Answer 373

tidal volume (VT)

Question 374

In a typical adult, about 70% of the tidal volume (350 mL)

Answer 374

actually reaches the respiratory zone of the respiratory system—the respiratory bronchioles, alveolar ducts, alveolar saccules, and alveoli—and participates in external respiration. The other 30% (150 mL) remains in the conducting airways of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles.

Question 375

anatomic (respiratory) dead space.

Answer 375

Collectively, the conducting airways with air that does not undergo respiratory exchange

Question 376

Not all of the inhaled air can be used in gas exchange because

Answer 376

some of it remains in the anatomic dead space.

Question 377

By taking a very deep breath, you can inhale a good deal more

Answer 377

than 500 mL. This additional inhaled air, called the inspiratory reserve volume (IRV), is about 3100 mL in an average adult male and 1900 mL in an average adult female

Question 378

If you inhale normally and then exhale as forcibly as possible

Answer 378

, you should be able to push out considerably more air in addition to the 500 mL of tidal volume The extra 1200 mL in males and 700 mL in females is called the expiratory reserve volume (ERV).

Question 379

The forced expiratory volume in 1 second (FEV1) is

Answer 379

the volume of air that can be exhaled from the lungs in 1 second with maximal effort following a maximal inhalation

Question 380

Even after the expiratory reserve volume is exhaled,

Answer 380

considerable air remains in the lungs because the subatmospheric intrapleural pressure keeps the alveoli slightly inflated, and some air remains in the noncollapsible airways. This volume, which cannot be measured by spirometry, is called the residual volume

Question 381

residual volume (re-ZID-u-al) (RV) amounts to

Answer 381

about 1200 mL in males and 1100 mL in females.

Question 382

If the thoracic cavity is opened, the intrapleural pressure rises to equal the atmospheric pressure and forces out some of the residual volume. The air remaining is called the

Answer 382

minimal volume.

Question 383

Minimal volume provides a medical and legal tool for

Answer 383

determining whether a baby is born dead (stillborn) or died after birth

Question 384

The presence of minimal volume can be demonstrated

Answer 384

by placing a piece of lung in water and observing if it floats. Fetal lungs contain no air, so the lung of a stillborn baby will not float in water.

Question 385

Inspiratory capacity (IC) is

Answer 385

the sum of tidal volume and inspiratory reserve volume (500 mL + 3100 mL = 3600 mL in males and 500 mL + 1900 mL = 2400 mL in females).

Question 386

Functional residual capacity (FRC) is

Answer 386

the sum of residual volume and expiratory reserve volume (1200 mL + 1200 mL = 2400 mL in males and 1100 mL + 700 mL = 1800 mL in females).

Question 387

Vital capacity (VC) is

Answer 387

the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume (4800 mL in males and 3100 mL in females).

Question 388

total lung capacity (TLC) is

Answer 388

the sum of vital capacity and residual volume (4800 mL + 1200 mL = 6000 mL in males and 3100 mL + 1100 mL = 4200 mL in females).

Question 389

Another way to assess pulmonary function is to determine

Answer 389

the amount of air that flows into and out of the lungs each minute. The minute ventilation ()—the total volume of air inspired and expired each minute

Question 390

the minute ventilation can be calculated by

Answer 390

tidal volume multiplied by respiratory rate.

Question 391

In a typical adult at rest, minute ventilation is about

Answer 391

6000 mL/min ( = 12 breaths per minute × 500 mL = 6000 mL/min). A lower-than-normal minute ventilation usually is a sign of pulmonary malfunction.

Question 392

The alveolar ventilation (A) is

Answer 392

the volume of air per minute that actually reaches the respiratory zone (350 mL). Alveolar ventilation is typically about 4200 mL/min (A = 12 breaths per minute × 350 mL = 4200 mL/min).

Question 393

The exchange of oxygen and carbon dioxide between alveolar air and pulmonary blood occurs via

Answer 393

passive diffusion, which is governed by the behavior of gases as described by two gas laws, Dalton’s law and Henry’s law.

Question 394

Dalton’s law is important for understanding

Answer 394

how gases move down their pressure gradients by diffusion

Question 395

Henry’s law helps explain

Answer 395

how the solubility of a gas relates to its diffusion.

Question 396

According to Dalton’s law,

Answer 396

each gas in a mixture of gases exerts its own pressure as if no other gases were present

Question 397

The pressure of a specific gas in a mixture is called

Answer 397

its partial pressure (Px); the subscript is the chemical formula of the gas.

Question 398

The total pressure of the mixture is calculated simply by

Answer 398

adding all of the partial pressures.

Question 399

Atmospheric air is

Answer 399

a mixture of gases—nitrogen (N2), oxygen (O2), argon (Ar), carbon dioxide (CO2), variable amounts of water vapor (H2O), plus other gases present in small quantities.

Question 400

We can determine the partial pressure exerted by each component in the mixture by

Answer 400

multiplying the percentage of the gas in the mixture by the total pressure of the mixture

Question 401

describe the concentration of different gases in atmospheric air

Answer 401

Atmospheric air is 78.6% nitrogen, 20.9% oxygen, 0.093% argon, 0.04% carbon dioxide, and 0.06% other gases; a variable amount of water vapor is also present.

Question 402

partial pressures determine the movement of

Answer 402

O2 and CO2 between the atmosphere and lungs, between the lungs and blood, and between the blood and body cells

Question 403

Each gas diffuses across a permeable membrane

Answer 403

from the area where its partial pressure is greater to the area where its partial pressure is less. The greater the difference in partial pressure, the faster the rate of diffusion.

Question 404

Compared with inhaled air, alveolar air has

Answer 404

less O2 (13.6% versus 20.9%) and more CO2 (5.2% versus 0.04%)

Question 405

Compared with inhaled air, alveolar air has less O2 (13.6% versus 20.9%) and more CO2 (5.2% versus 0.04%) for two reasons.

Answer 405

First, gas exchange in the alveoli increases the CO2 content and decreases the O2 content of alveolar air. Second, when air is inhaled it becomes humidified as it passes along the moist mucosal linings.

Question 406

exhaled air contains

Answer 406

more O2 than alveolar air (16% versus 13.6%) and less CO2 (4.5% versus 5.2%) because some of the exhaled air was in the anatomic dead space and did not participate in gas exchange.

Question 407

Exhaled air is

Answer 407

a mixture of alveolar air and inhaled air that was in the anatomic dead space.

Question 408

Henry’s law states that

Answer 408

the quantity of a gas that will dissolve in a liquid is proportional to the partial pressure of the gas and its solubility.

Question 409

In body fluids, the ability of a gas to stay in solution is

Answer 409

greater when its partial pressure is higher and when it has a high solubility in water.

Question 410

The higher the partial pressure of a gas over a liquid and the higher the solubility,

Answer 410

the more gas will stay in solution.

Question 411

In comparison to oxygen, much more CO2 is dissolved in blood plasma because

Answer 411

the solubility of CO2 is 24 times greater than that of O2.

Question 412

Even though the air we breathe contains mostly N2,

Answer 412

this gas has no known effect on bodily functions, and at sea level pressure very little of it dissolves in blood plasma because its solubility is very low.

Question 413

A major clinical application of Henry’s law is

Answer 413

hyperbaric oxygenation (hyper- = over; -baros = pressure), the use of pressure to cause more O2 to dissolve in the blood

Question 414

What causes nitrogen narcosis or rapture of the deep

Answer 414

When a scuba diver breathes air under high pressure, the nitrogen in the mixture can have serious negative effects. Because the partial pressure of nitrogen is higher in a mixture of compressed air than in air at sea level pressure, a considerable amount of nitrogen dissolves in plasma and interstitial fluid. Excessive amounts of dissolved nitrogen may produce giddiness and other symptoms similar to alcohol intoxication

Question 415

If a diver comes to the surface slowly, the dissolved nitrogen can be eliminated by exhaling it. However, if the ascent is too rapid,

Answer 415

nitrogen comes out of solution too quickly and forms gas bubbles in the tissues, resulting in decompression sickness (the bends).

Question 416

External respiration or pulmonary gas exchange

Answer 416

is the diffusion of O2 from air in the pulmonary alveoli of the lungs to blood in pulmonary capillaries and the diffusion of CO2 in the opposite direction

Question 417

External respiration in the lungs converts

Answer 417

deoxygenated blood (depleted of some O2) coming from the right side of the heart into oxygenated blood (saturated with O2) that returns to the left side of the heart

Question 418

As blood flows through the pulmonary capillaries,

Answer 418

it picks up O2 from pulmonary alveolar air and unloads CO2 into pulmonary alveolar air. Although this process is commonly called an “exchange” of gases, each gas diffuses independently from the area where its partial pressure is higher to the area where its partial pressure is lower.

Question 419

O2 diffuses from pulmonary alveolar air, where its partial pressure is 105 mmHg, into

Answer 419

the blood in pulmonary capillaries, where PO2 is only 40 mmHg in a resting person. If you have been exercising, the PO2 will be even lower because contracting muscle fibers are using more O2. Diffusion continues until the PO2 of pulmonary capillary blood increases to match the PO2 of alveolar air, 105 mmHg

Question 420

Since blood leaving pulmonary capillaries near pulmonary alveolar air spaces mixes with a small volume of blood that has flowed through conducting portions of the respiratory system, where gas exchange does not occur,

Answer 420

the PO2 of blood in the pulmonary veins is slightly less than the PO2 in pulmonary capillaries, about 100 mmHg.

Question 421

While O2 is diffusing from pulmonary alveolar air into deoxygenated blood,

Answer 421

CO2 is diffusing in the opposite direction.

Question 422

The PCO2 of deoxygenated blood is 45 mmHg in a resting person,

Answer 422

and the PCO2 of pulmonary alveolar air is 40 mmHg

Question 423

Because of this difference in PCO2, between deoxygenated blood and pulmonary aveolar air,

Answer 423

carbon dioxide diffuses from deoxygenated blood into the pulmonary alveoli until the PCO2 of the blood decreases to 40 mmHg. Exhalation keeps alveolar PCO2 at 40 mmHg. Oxygenated blood returning to the left side of the heart in the pulmonary veins thus has a PCO2 of 40 mmHg.

Question 424

The number of capillaries near pulmonary alveoli in the lungs is

Answer 424

very large, and blood flows slowly enough through these capillaries that it picks up a maximal amount of O2.

Question 425

During vigorous exercise, when cardiac output is increased,

Answer 425

blood flows more rapidly through both the systemic and pulmonary circulations. As a result, blood’s transit time in the pulmonary capillaries is shorter. Still, the PO2 of blood in the pulmonary veins normally reaches 100 mmHg.

Question 426

In diseases that decrease the rate of gas diffusion,

Answer 426

the blood may not come into full equilibrium with pulmonary alveolar air, especially during exercise. When this happens, the PO2 declines and PCO2 rises in systemic arterial blood.

Question 427

The left ventricle

Answer 427

pumps oxygenated blood into the aorta and through the systemic arteries to systemic capillaries.

Question 428

The exchange of O2 and CO2 between systemic capillaries and tissue cells is called

Answer 428

internal respiration or systemic gas exchange

Question 429

As O2 leaves the bloodstream,

Answer 429

oxygenated blood is converted into deoxygenated blood.

Question 430

Unlike external respiration, which occurs only in the lungs, internal respiration

Answer 430

occurs in tissues throughout the body.

Question 431

The PO2 of blood pumped into systemic capillaries is higher (100 mmHg) than

Answer 431

the PO2 in tissue cells (40 mmHg at rest) because the cells constantly use O2 to produce ATP. Due to this pressure difference, oxygen diffuses out of the capillaries into tissue cells and blood PO2 drops to 40 mmHg by the time the blood exits systemic capillaries.

Question 432

While O2 diffuses from the systemic capillaries into tissue cells,

Answer 432

CO2 diffuses in the opposite direction. Because tissue cells are constantly producing CO2, the PCO2 of cells (45 mmHg at rest) is higher than that of systemic capillary blood (40 mmHg). As a result, CO2 diffuses from tissue cells through interstitial fluid into systemic capillaries until the PCO2 in the blood increases to 45 mmHg. The deoxygenated blood then returns to the heart and is pumped to the lungs for another cycle of external respiration.

Question 433

In a person at rest, tissue cells, on average, need

Answer 433

only 25% of the available O2 in oxygenated blood; despite its name, deoxygenated blood retains 75% of its O2 content.

Question 434

During exercise,

Answer 434

more O2 diffuses from the blood into metabolically active cells, such as contracting skeletal muscle fibers. Active cells use more O2 for ATP production, causing the O2 content of deoxygenated blood to drop below 75%.

Question 435

The rate of pulmonary and systemic gas exchange depends on several factors.

Answer 435

Partial pressure difference of the gases.
Surface area available for gas exchange
Diffusion distance.
Molecular weight and solubility of the gases.

Question 436

Alveolar PO2 must be higher than blood PO2 for

Answer 436

oxygen to diffuse from pulmonary alveolar air into the blood.

Question 437

The rate of diffusion is faster when

Answer 437

the difference between PO2 in pulmonary alveolar air and pulmonary capillary blood is larger; diffusion is slower when the difference is smaller.

Question 438

many capillaries surround

Answer 438

each pulmonary alveolus, so many that as much as 900 mL of blood is able to participate in gas exchange at any instant

Question 439

The respiratory membrane is very thin, so

Answer 439

diffusion occurs quickly. Also, the capillaries are so narrow that the red blood cells must pass through them in single file, which minimizes the diffusion distance from a pulmonary alveolar air space to hemoglobin inside red blood cells.

Question 440

Because O2 has a lower molecular weight than CO2, it could be expected to diffuse across the respiratory membrane about 1.2 times faster. However,

Answer 440

the solubility of CO2 in the fluid portions of the respiratory membrane is about 24 times greater than that of O2. Taking both of these factors into account, net outward CO2 diffusion occurs 20 times more rapidly than net inward O2 diffusion. Consequently, when diffusion is slower than normal—for example, in emphysema or pulmonary edema—O2 insufficiency (hypoxia) typically occurs before there is significant retention of CO2 (hypercapnia).

Question 441

When O2 and CO2 enter the blood,

Answer 441

certain chemical reactions occur that aid in gas transport and gas exchange.

Question 442

Oxygen does not dissolve easily in water, so

Answer 442

only about 1.5% of inhaled O2 is dissolved in blood plasma, which is mostly water.

Question 443

About 98.5% of blood O2

Answer 443

is bound to hemoglobin in red blood cells (Figure 23.18). Each 100 mL of oxygenated blood contains the equivalent of 20 mL of gaseous O2. Using the percentages just given, the amount dissolved in the plasma is 0.3 mL and the amount bound to hemoglobin is 19.7 mL.

Question 444

Most O2 is transported by hemoglobin as

Answer 444

oxyhemoglobin (Hb–O2) within red blood cells;

Question 445

most CO2 is transported in blood plasma as

Answer 445

bicarbonate ions (HCO3−)

Question 446

The heme portion of hemoglobin contains

Answer 446

four atoms of iron, each capable of binding to a molecule of O2

Question 447

Oxygen and hemoglobin

Answer 447

bind in an easily reversible reaction to form oxyhemoglobin:

Question 448

The 98.5% of the O2 that is bound to hemoglobin is trapped inside RBCs, so

Answer 448

only the dissolved O2 (1.5%) can diffuse out of tissue capillaries into tissue cells.

Question 449

The most important factor that determines how much O2 binds to hemoglobin is

Answer 449

the PO2: the higher the PO2, the more O2 combines with Hb.

Question 450

When reduced hemoglobin (Hb) is completely converted to oxyhemoglobin (Hb–O2),

Answer 450

the hemoglobin is said to be fully saturated;

Question 451

when hemoglobin consists of a mixture of Hb and Hb–O2

Answer 451

, it is partially saturated.

Question 452

The percent saturation of hemoglobin expresses

Answer 452

the average saturation of hemoglobin with oxygen

Question 453

if each hemoglobin molecule has bound two O2 molecules,

Answer 453

then the hemoglobin is 50% saturated because each Hb can bind a maximum of four O2.

Question 454

The relationship between the percent saturation of hemoglobin and PO2 is illustrated in

Answer 454

the oxygen–hemoglobin dissociation curve

Question 455

when the PO2 is high,

Answer 455

hemoglobin binds with large amounts of O2 and is almost 100% saturated.

Question 456

When PO2 is low,

Answer 456

hemoglobin is only partially saturated.

Question 457

the greater the PO2,

Answer 457

the more O2 will bind to hemoglobin, until all the available hemoglobin molecules are saturated.

Question 458

in pulmonary capillaries, where PO2 is high,

Answer 458

a lot of O2 binds to hemoglobin.

Question 459

In tissue capillaries, where the PO2 is lower,

Answer 459

hemoglobin does not hold as much O2, and the dissolved O2 is unloaded via diffusion into tissue cells

Question 460

As PO2 increases,

Answer 460

more O2 combines with hemoglobin.

Question 461

When the PO2 is between 60 and 100 mmHg,

Answer 461

hemoglobin is 90% or more saturated with O2

Question 462

blood picks up a nearly full load of O2 from the lungs

Answer 462

even when the PO2 of alveolar air is as low as 60 mmHg.

Question 463

The Hb–PO2 curve explains

Answer 463

why people can still perform well at high altitudes or when they have certain cardiac and pulmonary diseases, even though PO2 may drop as low as 60 mmHg.

Question 464

Between 40 and 20 mmHg,

Answer 464

large amounts of O2 are released from hemoglobin in response to only small decreases in PO2.

Question 465

In active tissues such as contracting muscles,

Answer 465

PO2 may drop well below 40 mmHg. Then, a large percentage of the O2 is released from hemoglobin, providing more O2 to metabolically active tissues.

Question 466

Although PO2 is the most important factor that determines the percent O2 saturation of hemoglobin,

Answer 466

several other factors influence the tightness or affinity with which hemoglobin binds O2

Question 467

The changing affinity of hemoglobin for O2 is another example of how

Answer 467

homeostatic mechanisms adjust body activities to cellular needs.

Question 468

metabolically active tissue cells

Answer 468

need O2 and produce acids, CO2, and heat as wastes.

Question 469

The following four factors affect the affinity of hemoglobin for O2:

Answer 469

acidity (pH)
Partial pressure of Carbon Dioxide
Temperature
2,3-bisphosphoglycerate (BPG)

Question 470

As acidity increases (pH decreases), the affinity of hemoglobin for O2

Answer 470

decreases, and O2 dissociates more readily from hemoglobin

Question 471

The main acids produced by metabolically active tissues are .

Answer 471

lactic acid and carbonic acid

Question 472

When pH decreases, the entire oxygen–hemoglobin dissociation curve

Answer 472

shifts to the right; at any given PO2, Hb is less saturated with O2, a change termed the Bohr effect (BŌR).

Question 473

The Bohr effect works both ways meaning:

Answer 473

An increase in H+ in blood causes O2 to unload from hemoglobin, and the binding of O2 to hemoglobin causes unloading of H+ from hemoglobin.

Question 474

CO2 also can bind to hemoglobin, and the effect is

Answer 474

similar to that of H+ (shifting the curve to the right). As PCO2 rises, hemoglobin releases O2 more readily

Question 475

PCO2 and pH are related factors because

Answer 475

low blood pH (acidity) results from high PCO2.

Question 476

As CO2 enters the blood,

Answer 476

much of it is temporarily converted to carbonic acid (H2CO3), a reaction catalyzed by an enzyme in red blood cells called carbonic anhydrase

Question 477

As the H+ concentration increases, pH decreases. Thus

Answer 477

, an increased PCO2 produces a more acidic environment, which helps release O2 from hemoglobin.

Question 478

During exercise,

Answer 478

lactic acid—a by-product of anaerobic metabolism within muscles—also decreases blood pH.

Question 479

Decreased PCO2 (and elevated pH)

Answer 479

shift the saturation curve to the left.

Question 480

As pH decreases or PCO2 increases,

Answer 480

the affinity of hemoglobin for O2 declines, so less O2 combines with hemoglobin and more is available to tissues.

Question 481

Within limits, as temperature increases,

Answer 481

so does the amount of O2 released from hemoglobin

Question 482

Heat is a by-product of the metabolic reactions of all cells,

Answer 482

and the heat released by contracting muscle fibers tends to raise body temperature

Question 483

Metabolically active cells require

Answer 483

more O2 and liberate more acids and heat. The acids and heat in turn promote release of O2 from oxyhemoglobin

Question 484

In contrast, during hypothermia (lowered body temperature)

Answer 484

cellular metabolism slows, the need for O2 is reduced, and more O2 remains bound to hemoglobin (a shift to the left in the saturation curve)

Question 485

A substance found in red blood cells called 2,3-bisphosphoglycerate (BPG) (bis′-fos-fō-GLIS-e-rāt), formerly called diphosphoglycerate (DPG),

Answer 485

decreases the affinity of hemoglobin for O2 and thus helps unload O2 from hemoglobin

Question 486

BPG is formed

Answer 486

in red blood cells when they break down glucose to produce ATP in a process called glycolysis

Question 487

When BPG combines with hemoglobin by binding to the terminal amino groups of the two beta globin chains,

Answer 487

the hemoglobin binds O2 less tightly at the heme group sites.

Question 488

The greater the level of BPG,

Answer 488

the more O2 is unloaded from hemoglobin.

Question 489

Certain hormones, such as ))________________ increase the formation of BPG.

Answer 489

thyroxine, human growth hormone, epinephrine, norepinephrine, and testosterone,

Question 490

The level of BPG also is higher in people

Answer 490

living at higher altitudes.

Question 491

Fetal hemoglobin (Hb-F) differs from adult hemoglobin (Hb-A) in

Answer 491

structure and in its affinity for O2

Question 492

Hb-F has a higher affinity for O2 because

Answer 492

it binds BPG less strongly.

Question 493

when PO2 is low,

Answer 493

Hb-F can carry up to 30% more O2 than maternal Hb-A

Question 494

As the maternal blood enters the placenta, O2 is readily transferred to fetal blood. This is very important because

Answer 494

the O2 saturation in maternal blood in the placenta is quite low, and the fetus might suffer hypoxia were it not for the greater affinity of fetal hemoglobin for O2.

Question 495

Carbon monoxide (CO) is

Answer 495

a colorless and odorless gas found in exhaust fumes from automobiles, gas furnaces and space heaters, and in tobacco smoke

Question 496

Elevated blood levels of CO cause

Answer 496

carbon monoxide poisoning, which can cause the lips and oral mucosa to appear bright cherry-red (the color of hemoglobin with carbon monoxide bound to it).

Question 497

Under normal resting conditions, each 100 mL of deoxygenated blood contains

Answer 497

the equivalent of 53 mL of gaseous CO2,

Question 498

gaseous CO2 is transported in the blood in three main forms

Answer 498

Dissolved CO2
Carbamino compounds
Bicarbonate ions

Question 499

The smallest percentage of gaseous CO2 —about 7%—is

Answer 499

dissolved in blood plasma. On reaching the lungs, it diffuses into alveolar air and is exhaled.

Question 500

about 23% of CO2,

Answer 500

combines with the amino groups of amino acids and proteins in blood to form carbamino compounds

Question 501

Because the most prevalent protein in blood is hemoglobin

Answer 501

(inside red blood cells), most of the CO2 transported as carbamino compounds is bound to hemoglobin.

Question 502

The main CO2 binding sites are

Answer 502

the terminal amino acids in the two alpha and two beta globin chains.

Question 503

Hemoglobin that has bound CO2 is termed

Answer 503

carbaminohemoglobin (Hb–CO2):

Question 504

The formation of carbaminohemoglobin is greatly influenced by

Answer 504

PCO2.

Question 505

in tissue capillaries PCO2 is relatively high,

Answer 505

which promotes formation of carbaminohemoglobin.

Question 506

in pulmonary capillaries,

Answer 506

PCO2 is relatively low, and the CO2 readily splits apart from globin and enters the alveoli by diffusion.

Question 507

The greatest percentage of CO2—about 70%—is transported in blood plasma as

Answer 507

bicarbonate ions

Question 508

As CO2 diffuses into systemic capillaries and enters red blood cells,

Answer 508

it reacts with water in the presence of the enzyme carbonic anhydrase (CA) to form carbonic acid, which dissociates into H+ and HCO3−:

Question 509

as blood picks up CO2,

Answer 509

HCO3− accumulates inside RBCs

Question 510

Some HCO3− moves out into the blood plasma, down its concentration gradient. In exchange,

Answer 510

chloride ions (Cl−) move from blood plasma into the RBCs. This exchange of negative ions, which maintains the electrical balance between blood plasma and RBC cytosol, is known as the chloride shift The net effect of these reactions is that CO2 is removed from tissue cells and transported in blood plasma as HCO3−. As blood passes through pulmonary capillaries in the lungs, all of these reactions reverse and CO2 is exhaled.

Question 511

The amount of CO2 that can be transported in the blood is influenced by

Answer 511

the percent saturation of hemoglobin with oxygen

Question 512

The lower the amount of oxyhemoglobin (Hb–O2),

Answer 512

the higher the CO2-carrying capacity of the blood, a relationship known as the Haldane effect.

Question 513

Two characteristics of deoxyhemoglobin give rise to the Haldane effect:

Answer 513

(1) Deoxyhemoglobin binds to and thus transports more CO2 than does Hb–O2. (2) Deoxyhemoglobin also buffers more H+ than does Hb–O2, thereby removing H+ from solution and promoting conversion of CO2 to HCO3− via the reaction catalyzed by carbonic anhydrase.

Question 514

Deoxygenated blood returning to the pulmonary capillaries in the lungs (Figure 23.23a) contains

Answer 514

CO2 dissolved in blood plasma, CO2 combined with globin as carbaminohemoglobin (Hb–CO2), and CO2 incorporated into HCO3− within RBCs

Question 515

The RBCs of deoxygenated blood returning to the pulmonary capillaries have also picked up

Answer 515

H+, some of which binds to and therefore is buffered by hemoglobin (Hb–H).

Question 516

As blood passes through the pulmonary capillaries,

Answer 516

molecules of CO2 dissolved in blood plasma and CO2 that dissociates from the globin portion of hemoglobin diffuse into pulmonary alveolar air and are exhaled.

Question 517

As CO2 is being exhaled, At the same time,

Answer 517

inhaled O2 is diffusing from pulmonary alveolar air into RBCs and is binding to hemoglobin to form oxyhemoglobin (Hb–O2). Carbon dioxide also is released from HCO3− when H+ combines with HCO3− inside RBCs.The H2CO3 formed from this reaction then splits into CO2, which is exhaled, and H2O.

Question 518

As the concentration of HCO3− declines inside RBCs in pulmonary capillaries,

Answer 518

HCO3− diffuses in from the blood plasma, in exchange for Cl−.

Question 519

In sum, oxygenated blood leaving the lungs

Answer 519

has increased O2 content and decreased amounts of CO2 and H+.

Question 520

In systemic capillaries, as cells use O2 and produce CO2,

Answer 520

the chemical reactions reverse

Question 521

Hemoglobin inside red blood cells transports

Answer 521

O2, CO2, and H+.

Question 522

At rest, ____________ of O2 is used each minute by body cells.

Answer 522

about 200 mL

Question 523

During strenuous exercise, O2 use

Answer 523

typically increases 15- to 20-fold in normal healthy adults, and as much as 30-fold in elite endurance-trained athletes.

Question 524

The size of the thorax is altered by

Answer 524

the action of the breathing muscles, which contract as a result of nerve impulses transmitted from centers in the brain and relax in the absence of nerve impulses. These nerve impulses are sent from clusters of neurons located bilaterally in the brain stem. This widely dispersed group of neurons, collectively called the respiratory center,

Question 525

the respiratory center, can be divided into two principal areas on the basis of location and function:

Answer 525

(1) the medullary respiratory center in the medulla oblongata and (2) the pontine respiratory group in the pons

Question 526

The medullary respiratory center is made up of two collections of neurons called

Answer 526

the dorsal respiratory group (DRG), formerly called the inspiratory area, and the ventral respiratory group (VRG), formerly called the expiratory area.

Question 527

During normal quiet breathing,

Answer 527

neurons of the DRG generate impulses to the diaphragm via the phrenic nerves and the external intercostal muscles via the intercostal nerves These impulses are released in bursts, which begin weakly, increase in strength for about two seconds, and then stop altogether.

Question 528

When the nerve impulses reach the diaphragm and external intercostals, from the DRG

Answer 528

the muscles contract and inhalation occurs.

Question 529

When the DRG becomes inactive after two seconds,

Answer 529

the diaphragm and external intercostals relax for about three seconds, allowing the passive recoil of the lungs and thoracic wall. Then, the cycle repeats itself.

Question 530

The respiratory center is composed of

Answer 530

neurons in the medullary respiratory center in the medulla plus the pontine respiratory group in the pons.

Question 531

Located in the VRG is a cluster of neurons called the pre-Bötzinger complex (BOT-zin-ger) that is believed to be important in

Answer 531

the generation of the rhythm of breathing

Question 532

the pre-Bötzinger complex

Answer 532

analogous to the one in the heart, is composed of pacemaker cells that set the basic rhythm of breathing. The exact mechanism of these pacemaker cells is unknown and is the topic of much ongoing research.

Question 533

it is thought that the pacemaker cells in the pre-Bötzinger complex

Answer 533

provide input to the DRG, driving the rate at which DRG neurons fire action potentials.

Question 534

The remaining neurons of the VRG that are not in the pre-Bötzinger complex

Answer 534

do not participate in normal quiet breathing

Question 535

The VRG becomes activated when

Answer 535

forceful breathing is required, such as during exercise, when playing a wind instrument, or at high altitudes.

Question 536

During forceful inhalation (Figure 23.25b), nerve impulses from the DRG not only stimulate the diaphragm and external intercostal muscles to contract, they also activate

Answer 536

neurons of the VRG involved in forceful inhalation to send impulses to the accessory muscles of inhalation (sternocleidomastoid, scalenes, and pectoralis minor). Contraction of these muscles results in forceful inhalation.

Question 537

During forceful exhalation

Answer 537

the DRG is inactive along with the neurons of the VRG that result in forceful inhalation.

Question 538

during forceful exhalation those neurons of the VRG involved in forceful exhalation send nerve impulses to the accessory muscles of exhalation (internal intercostals, external abdominal oblique, internal abdominal oblique, transversus abdominis, and rectus abdominis).

Question 539

The pontine respiratory group (PRG) (PON-tēn), formerly called the pneumotaxic area, is

Answer 539

a collection of neurons in the pons

Question 540

The neurons in the PRG are active during

Answer 540

inhalation and exhalation.

Question 541

The PRG

Answer 541

transmits nerve impulses to the DRG in the medulla

Question 542

The PRG may play a role in both inhalation and exhalation by

Answer 542

modifying the basic rhythm of breathing generated by the VRG, as when exercising, speaking, or sleeping.

Question 543

Activity of the respiratory center can be modified in response to

Answer 543

inputs from other brain regions, receptors in the peripheral nervous system, and other factors in order to maintain the homeostasis of breathing.

Question 544

Since the cerebral cortex has connections with the respiratory center,

Answer 544

we can voluntarily alter our pattern of breathing.

Question 545

Voluntary control is protective because

Answer 545

it enables us to prevent water or irritating gases from entering the lungs.

Question 546

The ability to not breathe is limited by

Answer 546

the buildup of CO2 and H+ in the body.

Question 547

When PCO2 and H+ concentrations increase to a certain level,

Answer 547

the DRG neurons of the medullary respiratory center are strongly stimulated, nerve impulses are sent along the phrenic and intercostal nerves to inspiratory muscles, and breathing resumes, whether the person wants it to or not.

Question 548

Nerve impulses from the hypothalamus and limbic system also stimulate the respiratory center, allowing

Answer 548

emotional stimuli to alter breathing as, for example, in laughing and crying.

Question 549

Certain chemical stimuli modulate

Answer 549

how quickly and how deeply we breathe.

Question 550

The respiratory system functions to

Answer 550

maintain proper levels of CO2 and O2 and is very responsive to changes in the levels of these gases in body fluids.

Question 551

Chemoreceptors in two locations of the respiratory system

Answer 551

monitor levels of CO2, H+, and O2 and provide input to the respiratory center

Question 552

Central chemoreceptors are located

Answer 552

in or near the medulla oblongata in the central nervous system. They respond to changes in H+ concentration or PCO2, or both, in cerebrospinal fluid.

Question 553

Peripheral chemoreceptors are located

Answer 553

in the aortic bodies, clusters of chemoreceptors located in the wall of the aortic arch, and in the carotid bodies, which are oval nodules in the wall of the left and right common carotid arteries where they divide into the internal and external carotid arteries.

Question 554

peripheral chemoreceptors

Answer 554

are sensitive to changes in PO2, H+, and PCO2 in the blood.

Question 555

Because CO2 is lipid-soluble,

Answer 555

it easily diffuses into cells where, in the presence of carbonic anhydrase, it combines with water (H2O) to form carbonic acid (H2CO3).

Question 556

Carbonic acid quickly breaks down into H+ and HCO3−. Thus,

Answer 556

an increase in CO2 in the blood causes an increase in H+ inside cells, and a decrease in CO2 causes a decrease in H+.

Question 557

Normally, the PCO2 in arterial blood

Answer 557

is 40 mmHg.

Question 558

If even a slight increase in PCO2 occurs—

Answer 558

a condition called hypercapnia (hī′-per-KAP-nē-a) or hypercarbia—the central chemoreceptors are stimulated and respond vigorously to the resulting increase in H+ level.

Question 559

The peripheral chemoreceptors also are stimulated by

Answer 559

both the high PCO2 and the rise in H+.

Question 560

In addition, the peripheral chemoreceptors (but not the central chemoreceptors) respond to a deficiency of

Answer 560

O2. When PO2 in arterial blood falls from a normal level of 100 mmHg but is still above 50 mmHg, the peripheral chemoreceptors are stimulated.

Question 561

Severe deficiency of O2

Answer 561

depresses activity of the central chemoreceptors and DRG, which then do not respond well to any inputs and send fewer impulses to the muscles of inhalation.

Question 562

As the breathing rate decreases or breathing ceases altogether,

Answer 562

PO2 falls lower and lower, establishing a positive feedback cycle with a possibly fatal result.

Question 563

The chemoreceptors participate in a negative feedback system that regulates

Answer 563

the levels of CO2, O2, and H+ in the blood

Question 564

As a result of increased PCO2, decreased pH (increased H+), or decreased PO2,

Answer 564

input from the central and peripheral chemoreceptors causes the DRG to become highly active, and the rate and depth of breathing increase.

Question 565

Rapid and deep breathing, called hyperventilation,

Answer 565

allows the inhalation of more O2 and exhalation of more CO2 until PCO2 and H+ are lowered to normal.

Question 566

If arterial PCO2 is lower than 40 mmHg—

Answer 566

a condition called hypocapnia or hypocarbia—the central and peripheral chemoreceptors are not stimulated, and stimulatory impulses are not sent to the DRG. As a result, DRG neurons set their own moderate pace until CO2 accumulates and the PCO2 rises to 40 mmHg.

Question 567

DRG neurons are more strongly stimulated when

Answer 567

PO2 is rising above normal than when PO2 is falling below normal.

Question 568

Chemoreceptors are

Answer 568

sensory neurons that respond to changes in the levels of certain chemicals in the body.

Question 569

An increase in arterial blood PCO2 stimulates

Answer 569

the dorsal respiratory group (DRG).

Question 570

As soon as you start exercising,

Answer 570

your rate and depth of breathing increase, even before changes in PO2, PCO2, or H+ level occur. The main stimulus for these quick changes in respiratory effort is input from proprioceptors, which monitor movement of joints and muscles.

Question 571

Nerve impulses from the proprioceptors

Answer 571

stimulate the DRG of the medulla. At the same time, axon collaterals (branches) of upper motor neurons that originate in the primary motor cortex (precentral gyrus) also feed excitatory impulses into the DRG.

Question 572

Hypoxia (hī-POK-sē-a; hypo- = under) is

Answer 572

a deficiency of O2 at the tissue level. Based on the cause, we can classify hypoxia into four types,

Question 573

Hypoxic hypoxia is caused by

Answer 573

a low PO2 in arterial blood as a result of high altitude, airway obstruction, or fluid in the lungs.

Question 574

In anemic hypoxia,

Answer 574

too little functioning hemoglobin is present in the blood, which reduces O2 transport to tissue cells. Among the causes are hemorrhage, anemia, and failure of hemoglobin to carry its normal complement of O2, as in carbon monoxide poisoning.

Question 575

In ischemic hypoxia (is-KĒ-mik),

Answer 575

blood flow to a tissue is so reduced that too little O2 is delivered to it, even though PO2 and oxyhemoglobin levels are normal.

Question 576

In histotoxic hypoxia (his-tō-TOK-sik),

Answer 576

the blood delivers adequate O2 to tissues, but the tissues are unable to use it properly because of the action of some toxic agent. One cause is cyanide poisoning, in which cyanide blocks an enzyme required for the use of O2 during ATP synthesis.

Question 577

Similar to those in the blood vessels, stretch-sensitive receptors called baroreceptors or stretch receptors are located in

Answer 577

the walls of bronchi and bronchioles.When these receptors become stretched during overinflation of the lungs, nerve impulses are sent along the vagus (X) nerves to the dorsal respiratory group (DRG) in the medullary respiratory center. In response, the DRG is inhibited and the diaphragm and external intercostals relax. As a result, further inhalation is stopped and exhalation begins.

Question 578

As air leaves the lungs during exhalation,

Answer 578

the lungs deflate and the stretch receptors are no longer stimulated. Thus, the DRG is no longer inhibited, and a new inhalation begins. This reflex is referred to as the inflation reflex or Hering–Breuer reflex (HER-ing BROY-er).

Question 579

In infants, the inflation reflex

Answer 579

appears to function in normal breathing.

Question 580

In adults, the inflation reflex is not activated until

Answer 580

tidal volume (normally 500 mL) reaches more than 1500 mL. Therefore, the reflex in adults is a protective mechanism that prevents excessive inflation of the lungs, for example, during severe exercise, rather than a key component in the normal control of breathing.

Question 581

What are some lesser factors that contribute to regulation of breathing

Answer 581

Limbic system stimulation
temperature
pain
stretching of the anal sphincter muscle
irritation of airways
blood pressure

Question 582

How does limbic system stimulation contribute to the regulation of breathing

Answer 582

Anticipation of activity or emotional anxiety may stimulate the limbic system, which then sends excitatory input to the DRG, increasing the rate and depth of breathing.

Question 583

How does temperature contribute to regulation of breathing

Answer 583

An increase in body temperature, as occurs during a fever or vigorous muscular exercise, increases the rate of breathing. A decrease in body temperature decreases breathing rate. A sudden cold stimulus (such as plunging into cold water) causes temporary apnea (AP-nē-a; a- = without; -pnea = breath), an absence of breathing.

Question 584

How does pain contribute to the regulation of breathing

Answer 584

A sudden, severe pain brings about brief apnea, but a prolonged somatic pain increases breathing rate. Visceral pain may slow the rate of breathing.

Question 585

How does stretching of the anal sphincter contribute to the regulation of breathing

Answer 585

This action increases the breathing rate and is sometimes used to stimulate respiration in a newborn baby or a person who has stopped breathing.

Question 586

How does irritation of the airways contribute to the regulation of breathing

Answer 586

Physical or chemical irritation of the pharynx or larynx brings about an immediate cessation of breathing followed by coughing or sneezing.

Question 587

how does blood pressure contribute to regulation of breathing

Answer 587

The carotid and aortic baroreceptors that detect changes in blood pressure have a small effect on breathing. A sudden rise in blood pressure decreases the rate of breathing, and a drop in blood pressure increases the breathing rate.

Question 588

The respiratory and cardiovascular systems make adjustments in response to

Answer 588

both the intensity and duration of exercise.

Question 589

as cardiac output rises,

Answer 589

the blood flow to the lungs, termed pulmonary perfusion, increases as well

Question 590

the O2 diffusing capacity, a measure of the rate at which O2 can diffuse from alveolar air into the blood,

Answer 590

may increase threefold during maximal exercise because more pulmonary capillaries become maximally perfused.

Question 591

During exercise

Answer 591

there is a greater surface area available for diffusion of O2 into pulmonary blood capillaries.

Question 592

When muscles contract during exercise,

Answer 592

they consume large amounts of O2 and produce large amounts of CO2

Question 593

During vigorous exercise,

Answer 593

O2 consumption and breathing both increase dramatically.

Question 594

At the onset of exercise,

Answer 594

an abrupt increase in breathing is followed by a more gradual increase.

Question 595

With moderate exercise, the increase is due mostly to an increase in

Answer 595

the depth of breathing rather than to increased breathing rate

Question 596

When exercise is more strenuous,

Answer 596

the frequency of breathing also increases.

Question 597

The abrupt increase in breathing at the start of exercise is due to

Answer 597

neural changes that send excitatory impulses to the dorsal respiratory group (DRG) of the medullary respiratory center in the medulla.

Question 598

The abrupt increase in breathing at the start of exercise is due to neural changes that send excitatory impulses to the dorsal respiratory group (DRG) of the medullary respiratory center in the medulla. These changes include

Answer 598

(1) anticipation of the activity, which stimulates the limbic system; (2) sensory impulses from proprioceptors in muscles, tendons, and joints; and (3) motor impulses from the primary motor cortex (precentral gyrus).

Question 599

The more gradual increase in breathing during moderate exercise is due to

Answer 599

chemical and physical changes in the bloodstream

Question 600

The more gradual increase in breathing during moderate exercise is due to chemical and physical changes in the bloodstream, including

Answer 600

(1) slightly decreased PO2, due to increased O2 consumption; (2) slightly increased PCO2, due to increased CO2 production by contracting muscle fibers; and (3) increased temperature, due to liberation of more heat as more O2 is utilized.

Question 601

During strenuous exercise,

Answer 601

HCO3− buffers H+ released by lactic acid in a reaction that liberates CO2, which further increases PCO2.

Question 602

At the end of an exercise session,

Answer 602

an abrupt decrease in breathing is followed by a more gradual decline to the resting level.

Question 603

At the end of an exercise session, an abrupt decrease in breathing is followed by a more gradual decline to the resting level. The initial decrease is due mainly to

Answer 603

changes in neural factors when movement stops or slows; the more gradual phase reflects the slower return of blood chemistry levels and temperature to the resting state.

Question 604

effects of smoking on the respiratory system:

Answer 604

Nicotine constricts terminal bronchioles, which decreases airflow into and out of the lungs.
Carbon monoxide in smoke binds to hemoglobin and reduces its oxygen-carrying capability.
Irritants in smoke cause increased mucus secretion by the mucosa of the bronchial tree and swelling of the mucosal lining, both of which impede airflow into and out of the lungs.
Irritants in smoke also inhibit the movement of cilia and destroy cilia in the lining of the respiratory system. Thus, excess mucus and foreign debris are not easily removed, which further adds to the difficulty in breathing. This leads to a smoker’s cough and contributes to the tendency for smokers to be sick more often than non-smokers. The irritants can also convert the normal respiratory epithelium into stratified squamous epithelium, which lacks cilia and goblet cells.
With time, smoking leads to destruction of elastic fibers in the lungs and is the prime cause of emphysema. These changes cause collapse of small bronchioles and trapping of air in alveoli at the end of exhalation. The result is less efficient gas exchange.

Question 605

At about 4 weeks of development,

Answer 605

the respiratory system begins as an outgrowth of the foregut (precursor of some digestive organs) just inferior to the pharynx. This outgrowth is called the respiratory bud

Question 606

The endoderm lining the respiratory bud gives rise to

Answer 606

the epithelium and glands of the trachea, bronchi, and pulmonary alveoli.

Question 607

Mesoderm surrounding the respiratory bud gives rise to

Answer 607

the connective tissue, cartilage, and smooth muscle of these structures.

Question 608

The epithelial lining of the larynx develops from

Answer 608

the endoderm of the respiratory bud

Question 609

the cartilages and muscles of the larynx originate from

Answer 609

the fourth and sixth pharyngeal arches, swellings on the surface of the embryo

Question 610

As the respiratory bud elongates, its distal end enlarges to form

Answer 610

a globular laryngotracheal diverticulum, which gives rise to the trachea.

Question 611

the tracheal bud divides into primary bronchial buds, which

Answer 611

branch repeatedly and develop into the bronchi. By 24 weeks, 17 orders of branches have formed and respiratory bronchioles have developed.

Question 612

During weeks 6 to 16,

Answer 612

all major elements of the lungs have formed, except for those involved in gaseous exchange (respiratory bronchioles, alveolar ducts, and pulmonary alveoli).Since breathing is not possible at this stage, fetuses born during this time cannot survive.

Question 613

During weeks 16 to 26,

Answer 613

lung tissue becomes highly vascular and respiratory bronchioles, alveolar ducts, and some primitive alveoli develop.

Question 614

Although it is possible for a fetus born near 26 weeks to survive if given intensive care,

Answer 614

death frequently occurs due to the immaturity of the respiratory and other systems.

Question 615

The respiratory system develops from

Answer 615

endoderm and mesoderm.

Question 616

From 26 weeks to birth,

Answer 616

many more primitive pulmonary alveoli develop; they consist of pneumocytes type I (main sites of gaseous exchange) and pneumocytes type II that produce surfactant.Blood capillaries also establish close contact with the primitive pulmonary alveoli.

Question 617

surfactant is necessary to

Answer 617

lower surface tension of alveolar fluid and thus reduce the tendency of pulmonary alveoli to collapse on exhalation

Question 618

Although surfactant production begins by 20 weeks

Answer 618

, it is present in only small quantities. Amounts sufficient to permit survival of a premature (preterm) infant are not produced until 26 to 28 weeks’ gestation.

Question 619

Infants born before 26 to 28 weeks are at high risk of

Answer 619

respiratory distress syndrome (RDS), in which the pulmonary alveoli collapse during exhalation and must be reinflated during inhalation

Question 620

At about 30 weeks

Answer 620

, mature pulmonary alveoli develop.

Question 621

it is estimated that only

Answer 621

about one-sixth of the full complement of pulmonary alveoli develop before birth; the remainder develop after birth during the first 8 years.

Question 622

As the lungs develop,

Answer 622

they acquire their pleural sacs

Question 623

The visceral pleura and the parietal pleura

Answer 623

develop from mesoderm. The space between the pleural layers is the pleural cavity.

Question 624

During development, breathing movements of the fetus cause

Answer 624

the aspiration of fluid into the lungs This fluid is a mixture of amniotic fluid, mucus from bronchial glands, and surfactant.

Question 625

At birth,

Answer 625

the lungs are about half-filled with fluid. When breathing begins at birth, most of the fluid is rapidly reabsorbed by blood and lymph capillaries and a small amount is expelled through the nose and mouth during delivery.

Question 626

With advancing age,

Answer 626

the airways and tissues of the respiratory tract, including the pulmonary alveoli, become less elastic and more rigid; the chest wall becomes more rigid as well. The result is a decrease in lung capacity.

Question 627

In fact, vital capacity (the maximum amount of air that can be exhaled after maximal inhalation)

Answer 627

can decrease as much as 35% by age 70.

Question 628

with advancing age how is the respiratory system affected

Answer 628

A decrease in blood level of O2, decreased activity of alveolar macrophages, and diminished ciliary action of the epithelium lining the respiratory tract occur.

Question 629

Because of age-related factors, elderly people

Answer 629

are more susceptible to pneumonia, bronchitis, emphysema, and other pulmonary disorders.

Question 630

Age-related changes in the structure and functions of the lung can also contribute to

Answer 630

an older person’s reduced ability to perform vigorous exercises, such as running.

Question 631

In the United States, lung cancer

Answer 631

is the leading cause of cancer death in both males and females, accounting for 160,000 deaths annually

Question 632

The most common type of lung cancer,

Answer 632

bronchogenic carcinoma (brong′-kō-JEN-ik), starts in the epithelium of the bronchial tubes

Question 633

Pneumonia (noo-MŌ-ne-a) is

Answer 633

an acute infection or inflammation of the pulmonary alveoli.

Question 634

Chronic obstructive pulmonary disease (COPD) is

Answer 634

a type of respiratory disorder characterized by chronic and recurrent obstruction of airflow, which increases airway resistance

Question 635

Emphysema (em-fi-SĒ-ma = blown up or full of air) is

Answer 635

a disorder characterized by destruction of the walls of the pulmonary alveoli, producing abnormally large air spaces that remain filled with air during exhalation.

Question 636

Chronic bronchitis is

Answer 636

a disorder characterized by excessive secretion of bronchial mucus accompanied by a productive cough (sputum is raised) that lasts for at least 3 months of the year for two successive years.

Question 637

Asthma (AZ-ma = panting) or bronchial asthma is

Answer 637

a disorder characterized by chronic airway inflammation, airway hypersensitivity to a variety of stimuli, and airway obstruction.

Question 638

The bacterium Mycobacterium tuberculosis (mī′-kō-bak-TĒR-ē-um)

Answer 638

produces an infectious, communicable disease called tuberculosis (TB) that most often affects the lungs and the pleurae but may involve other parts of the body.

Question 639

Pulmonary edema is

Answer 639

an abnormal accumulation of fluid in the interstitial spaces and pulmonary alveoli

Question 640

Sudden infant death syndrome (SIDS) is

Answer 640

the sudden, unexpected death of an apparently healthy infant during sleep

Question 641

Severe acute respiratory syndrome (SARS) is

Answer 641

an example of an emerging infectious disease, that is, a disease that is new or changing.

Question 642

Malignant mesothelioma (mē-zō-thē-lē-OMA) is

Answer 642

a rare form of cancer that affects the mesothelium (simple squamous epithelium) of a serous membrane.