CHAPTER 25
Answers to “What Did You Learn?”
1.
In addition to gas exchange, the respiratory system: (1) conditions (warms,
humidifies, cleanses) inhaled gases; (2) produces sound by moving gasses through
the larynx; (3) participates in olfaction (sense of smell); and (4) helps protects the
body against pathogens, airborne allergens, and foreign particulate materials.
2.
The mucus lubricates the epithelial surface and prevents its dehydration. Mucus
traps inhaled dust, dirt particles, microorganisms, and pollen, and also humidifies
the inhaled air.
3.
Inhaled gases are warmed, humidified, and cleansed of particles as they travel
through the respiratory system.
4.
Nasal conchae help produce air turbulence in the nasal cavity. Because of the
turbulence, the air remains in the nasal cavity for a longer period of time, allowing
it to come into contact with the mucosa and become conditioned. Without the
nasal conchae, air would pass quickly through the nasal cavity and not be
sufficiently conditioned before entering the rest of the respiratory system.
5.
Swallowed material from the oral cavity and oropharynx is blocked from entering
the nasopharynx by the soft palate of the mouth. When swallowing, skeletal
muscles in the soft palate contract, elevating the soft palate and sealing off the
nasopharynx to prevent food from entering it.
6.
The vocal folds vibrate to produce sound when air passes between them while
they are adducted.
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7.
The walls of the bronchi are lined by a pseudostratified ciliated columnar
epithelium and supported by incomplete rings of hyaline cartilage that become
less numerous and smaller as the bronchi continue to divide. In addition, a
complete ring of smooth muscle develops between the mucosa of the airways and
the cartilaginous support in the wall. Bronchioles have a simple columnar or
simple cuboidal epithelium, no cartilage in their walls, thicker smooth muscle
compared with that of large bronchi, and separation of groups of smooth muscle
cells by connective tissue.
8.
Terminal bronchioles are the last strictly conducting passageway in the respiratory
system. They affect air resistance by either constricting or dilating. They are
small in diameter with continuous walls containing a thick layer of smooth
muscle. Respiratory bronchioles continue to have a conducting function, and they
are the first respiratory portion of the respiratory system. They have alveoli
outpocketings in their walls where gas exchange occurs.
9.
The hilum is a vertical, indented opening in the mediastinal surface of the lung.
Through this opening pass the bronchi, pulmonary vessels, lymphatic vessels, and
nerves. Collectively, all structures passing through the hilum are termed the “root
of the lung.”
10.
Pulmonary ventilation refers to the movement of air into and out of the respiratory
tract, and is also known as breathing.
11.
The diaphragm contracts during inhalation, causing a vertical dimensional change
to the thorax. The external intercostals elevate the ribs in general, while the
scalenes elevate the first and second ribs, causing lateral dimensional changes.
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Finally, a slight
anterior-posterior dimensional change to the thoracic cavity occurs due to anterior
movement of the inferior portion of the sternum during inhalation.
12.
The main function of sympathetic innervation to the lungs is bronchodilation
(increase in the airway diameter of the bronchioles).
13.
The dorsal respiratory group (DRG) is the inspiratory center. The ventral
respiratory group (VRG) is the expiratory center. During normal, quiet breathing,
the DRG is activated. The VRG, however, functions only during forced
exhalation. During normal quiet breathing, the VRG is inactive, and exhalation is
a passive event that does not require nervous stimulation.
14.
Due to aging, in the amount of gas that can be exchanged with each breath and the
ventilation rate both decrease. In some conditions, such as emphysema, there are
fewer alveoli, which causes a reduced capacity for gas exchange. Additionally, a
lifetime of carbon, dust, and pollution accumulation causes some of the lymph
nodes in the lungs to turn black, resulting in a speckled appearance to the lungs,
even in nonsmokers. Some alveolar epithelial cells die and are replaced by
connective tissue, thus further reducing the lungs’ capacity for gas exchange.
Answers to “Content Review”
1.
Mucous covers the respiratory epithelium where it acts as a lubricant and prevents
dehydration. The layer of sticky mucus traps foreign particles and humidifies the
inhaled air. If we are exposed to airborne allergens, large quantities of small
particulate material, irritating gases, or pathogens, the rate of mucin production
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increases.
2.
Nonkeratinized stratified squamous epithelium lines the oropharnx because this
epithelium is strong enough to withstand the abrasion of swallowed food.
3.
Increasing the tautness/tension on the vocal folds increases the pitch of the sound
produced. Conversely, the less taut/tense the vocal folds, the less the vocal folds
vibrate and the lower the pitch of the sound. The loudness of the sound is
dependent upon the force of the air passing across the surface of the vocal folds.
A large volume of air forced past the vocal folds causes a loud sound is produced.
4.
The bronchial tree, from largest structure to smallest, consists of primary bronchi,
secondary bronchi, tertiary bronchi, bronchioles, and finally the terminal
bronchioles.
5.
The bronchioles have such a small diameter that they do not need wall support
from cartilage since they will not collapse during inhalation.
6.
Alveolar type II cells, also called septal cells, secrete pulmonary surfactant onto
the alveolar surface. This material helps reduce surface tension to prevent the
collapse of the small air sacs.
7.
The left lung is slightly smaller than the right lung. Its medial surface indentation,
called the cardiac impression, accommodates the presence of the heart. The right
lung has three lobes [superior, middle, and inferior lobes] while the left lung has
only two [a superior lobe and an inferior lobe].
8.
In general, the thoracic cavity becomes larger when you inhale, and smaller when
you exhale. Vertical dimensional changes occur with movements of the
diaphragm. The diaphragm contracts during inhalation, and relaxes and is
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brought back to its original position during exhalation.
Lateral dimensional
changes occur during inhalation when the ribs are elevated. The external
intercostals elevate the ribs in general, while the scalenes elevate the 1st and 2nd
ribs specifically during inhalation. During normal exhalation, the ribs are brought
back to original position merely by relaxation of the external intercostals and
scalenes. However, the internal intercostals depress the ribs during forced
exhalation. Finally, there is a slight anterior-posterior dimensional change to the
thoracic cavity, due to an anterior movement of the inferior portion of the sternum
during inhalation. During exhalation, the inferior portion of the sternum moves
posteriorly and returns to its original position.
9.
The autonomic nervous system respiratory centers in the pons are the apneustic
area and pneumotaxic area. The apneustic and the pneumotaxic areas influence
the ventilation rate by modifying the activity of the rhythmicity center in the
medulla oblongata.
10.
The dorsal respiratory group (DRG) is the inspiratory center. The ventral
respiratory group (VRG) is the expiratory center. Both comprise the respiratory
rhythmicity center. The DRG controls the motor neurons that stimulate the
muscles of inspiration, and is activated during both normal inhalation and forced,
active inhalation. In contrast, the VRG functions only during forced exhalation.
During normal quiet breathing, the VRG is inactive and exhalation is a passive
event that does not require nervous stimulation.
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