770
UNIT FIVE
b. The amount of air that moves in or out during a
respiratory cycle is the tidal volume.
c. Additional air that can be inhaled is the inspiratory
reserve volume; additional air that can be exhaled
is the expiratory reserve volume.
d. Residual air remains in the lungs and is mixed with
newly inhaled air.
e. The total lung capacity is equal to the vital
capacity plus the residual air volume.
f. The inspiratory capacity is the maximum volume
of air a person can inhale following exhalation of
the tidal volume.
g. The functional residual capacity is the volume
of air that remains in the lungs following the
exhalation of the tidal volume.
h. The vital capacity is the maximum amount of air a
person can exhale after taking the deepest breath
possible.
i. Air in the anatomic and alveolar dead spaces is not
available for gas exchange.
4. Alveolar ventilation
a. Minute ventilation is tidal volume multiplied by
breathing rate.
b. Alveolar ventilation rate is the physiologic dead
space subtracted from the tidal volume multiplied
by breathing rate.
c. The alveolar ventilation rate is a major factor
affecting gas exchange between the alveolar air
and the blood.
5. Nonrespiratory air movements
a. Nonrespiratory air movements are air movements
other than breathing.
b. They include coughing, sneezing, laughing, crying,
hiccupping, and yawning.
19.5
CONTROL OF BREATHING (PAGE 755)
Normal breathing is rhythmic and involuntary, although
the respiratory muscles can be controlled voluntarily.
1. Respiratory areas
a. The respiratory areas are in the brainstem and
include parts of the medulla oblongata and pons.
b. The medullary respiratory center includes two
groups of neurons.
(1) The dorsal respiratory group is most important
in inspiration.
(2) The ventral respiratory group increases
inspiratory and expiratory movements during
forceful breathing.
c. The pontine respiratory group may contribute to
the rhythm of breathing.
2. Factors affecting breathing
a. The partial pressure of a gas is determined by the
concentration of that gas in a mixture of gases or
the concentration of gas dissolved in a liquid.
b. Chemicals, lung tissue stretching, and emotional
state affect breathing.
c. Chemosensitive areas (central chemoreceptors) are
associated with the respiratory center.
(1) CO
2
combines with water to form carbonic
acid, which, in turn, releases hydrogen ions in
the CSF.
(2) Stimulation of these areas increases alveolar
ventilation.
6. Trachea
a. The trachea extends into the thoracic cavity in
front of the esophagus.
b. It divides into the right and left bronchi.
c. The mucous lining continues to ┬▒
lter incoming air.
d. Incomplete cartilaginous rings support the wall.
7. Bronchial tree
a. The bronchial tree consists of branched air
passages that connect the trachea to the air sacs.
b. The branches of the bronchial tree include primary
bronchi, lobar bronchi, segmental bronchi,
intralobular bronchioles, terminal bronchioles,
respiratory bronchioles, alveolar ducts, alveolar
sacs, and alveoli.
c. Structure of the respiratory tubes
(1) As tubes branch, the amount of cartilage in
the walls decreases, and the muscular layer
becomes more prominent.
(2) Elastic ┬▒
bers in the walls aid breathing.
(3) The epithelial lining changes from
pseudostrati┬▒
ed and ciliated to cuboidal
and simple squamous as the tubes become
progressively smaller.
d. Functions of the respiratory tubes include
distribution of air and exchange of gases between
the alveolar air and the blood.
8. Lungs
a. The left and right lungs are separated by the
mediastinum and are enclosed by the diaphragm
and the thoracic cage.
b. The visceral pleura is attached to the surface of the
lungs; parietal pleura lines the thoracic cavity.
c. The right lung has three lobes, and the left lung
has two.
d. Each lobe is composed of lobules that contain
alveolar ducts, alveolar sacs, alveoli, nerves, blood
vessels, lymphatic vessels, and connective tissues.
19.4
BREATHING MECHANISM (PAGE 747)
Inspiration and expiration movements are accompanied
by changes in the size of the thoracic cavity.
1. Inspiration
a. Atmospheric pressure forces air into the lungs.
b. Inspiration occurs when the intra-alveolar pressure
is reduced.
c. The intra-alveolar pressure is reduced when the
diaphragm moves downward and the thoracic cage
moves upward and outward.
d. Surface tension holding the pleural membranes
together aids lung expansion.
e. Surfactant reduces surface tension in the alveoli.
2. Expiration
a. The forces of expiration come from the elastic
recoil of tissues and from surface tension in the
alveoli.
b. Expiration can be aided by thoracic and abdominal
wall muscles that pull the thoracic cage downward
and inward and compress the abdominal organs
inward and upward.
3. Respiratory air volumes and capacities
a. One inspiration followed by one expiration is a
respiratory cycle.
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