Chapter 20
Control of Respiratory Function
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Lung Functions
• Gas exchange
– Moves O2 into blood
– Removes CO2 from blood
• Blood storage
• Regulate vasoconstricting substances
– Bradykinin
– Angiotensin II
– Heparin
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Conducting Airways
• Move air into
lungs
• Warm and
humidify air
• Trap inhaled
particles
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Respiratory
Airways
• Bronchioles
• Alveoli
• Gas is
exchanged with
the blood
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Membranes and Cavities
• Parietal pleura
• Visceral pleura
• Pleural space
(between pleurae)
• Mediastinum
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Question
Which serous membrane lines the thoracic cavity?
a. Visceral pleura
b. Parietal pleura
c. Visceral mediastinum
d. Parietal mediastinum
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Answer
b. Parietal pleura
Rationale: The organs and walls of the thoracic and
abdominal cavities are covered with serous membranes.
Visceral membranes cover the organ; parietal
membranes line the cavity walls. The two membranes
and the space between them allow for ease of
movement. The thoracic cavity is lined by parietal
pleura; the lungs are covered by visceral pleura.
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Respiratory Muscles
• Diaphragm
• Accessory muscles of inhalation
– External intercostals
– Scalene
– Sternocleidomastoid
• Accessory muscles of exhalation
– Internal intercostals
– Abdominal muscles
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Question
Tell whether the following statement is true or false.
During inhalation, the diaphragm contracts and flattens.
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Answer
True
Rationale: The diaphragm is the main muscle of
inhalation/inspiration. During inhalation, the diaphragm
contracts and flattens (it moves downward in order to
accommodate the volume of air you are taking in,
allowing space for the lungs to expand). During
exhalation, the diaphragm relaxes and moves back up.
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Compliance
• How easily lungs can be inflated depends
on:
– Elastin and collagen fibers
– Water content
– Surface tension
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Surfactant Reduces Surface Tension
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Scenario
• A man’s lungs were damaged during a fire
• He developed severe respiratory distress
• The doctor said smoke inhalation had caused an inflammation
of his alveoli
• The damage had also destroyed some of his surfactant
Question:
• What had happened to his lung compliance?
• Why was he given positive-pressure ventilation?
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Lung Volumes
• Tidal volume
• Inspiratory reserve
• Expiratory reserve
• Residual volume
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Lung Capacities
• Vital capacity
• Inspiratory capacity
• Functional residual capacity
• Total lung capacity
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Dynamic Lung Function
• Forced vital capacity
• Forced expiratory volume
• FEV1.0
• Minute volume
• Maximum voluntary ventilation
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Question
Which measure of lung function indicates the total amount
of air that the lungs can hold?
a. Tidal volume
b. Functional residual capacity
c. Vital capacity
d. Total lung capacity
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Answer
d. Total lung capacity
Rationale: Total lung capacity is the maximum amount of
air that the lungs can hold—everything (volume-wise) at
the end of a maximal inhalation (the deepest breath one
can possibly take). Normal TLC is approximately 6 L.
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Gas Exchange
• Oxygen moves from
alveolar air into blood
• Carbon dioxide moves
from blood into alveolar
air
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Ventilation and Perfusion
Scenario:
A child has inhaled a peanut, blocking her left primary
bronchus.
Question:
• How will the ventilation in her two lungs change?
• How will the composition of the air in her two lungs differ?
• Which lung should she send more blood to?
• How should her body alter perfusion of the lungs?
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Ventilation–Perfusion Mismatching
• Blood goes to
parts of the lung
that do not have
oxygen to give it
• Blood does not
go to parts of
the lung that
have oxygen
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Question
Tell whether the following statement is true or false.
Ventilation–perfusion mismatch results in hypoxia.
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Answer
True
Rationale: In either case (ventilation without perfusion or
perfusion without ventilation), oxygen is not picked up by
the capillaries and delivered to the tissues. The result of
decreased oxygen at the tissue level is termed hypoxia.
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Blood Gases—Oxygen
• Dissolved oxygen = PaO2 or PO2
– Normal value >80 mm Hg
• Oxygen bound to hemoglobin = oxyhemoglobin
– Normal value 95% to 97% saturation
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Hemoglobin Holds Four Oxygen Molecules
O2
O2
O2
• How saturated is
this molecule of
hemoglobin?
• How could a person
have a hemoglobin
saturation of 95%?
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Oxygen Capacity
• Amount of oxygen
the blood can hold
• What is the oxygen
capacity of normal
blood?
• What is the oxygen
capacity of anemic
blood?
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Oxygen Release
• If the blood
released half of its
oxygen to the
tissues:
– How much
oxygen would
the normal
tissues receive?
– How much would
the anemic
person’s tissues
receive?
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Oxygen Release (cont.)
• Most body
tissues have a
PO2 of 40–60
mm Hg
• How much
oxygen does the
normal blood
release at a PO2
of 40 mm Hg?
• The anemic
blood?
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Oxygen Affinity
A
B
C
• How tightly the
hemoglobin
holds onto the
oxygen
• Which of these
hemoglobin
samples has the
highest oxygen
affinity?
• Which will
release the most
oxygen to the
tissues?
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Blood Gases—Carbon Dioxide
• Dissolved carbon dioxide = PaCO2 or PCO2
– Normal value 35–45 mm Hg
• Carbon dioxide bound to hemoglobin =
carbaminohemoglobin
• Carbonic acid  bicarbonate ion and H+
• When you exhale you remove CO2 from your blood
and also decrease the amount of carbonic acid, raising
your blood pH
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Question
Tell whether the following statement is true or false.
The relationship between PCO2 and pH is direct.
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Answer
False
Rationale: The relationship is indirect. As PCO2 levels rise,
the amount of carbonic acid in the blood increases,
making the pH more acidic (decreasing it).
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lungs
inflate
stretch receptors
note increased lung
volume
pneumotaxic
begins inspiration
respiratory
centers
apneustic
stretch receptors
note decreased lung
volume
stops inspiration;
begins exhalation
lungs
deflate
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Chemoreceptors Can Adjust Respiration
Rate
• Central chemoreceptors
– Measure PCO2 and pH in cerebrospinal fluid
– Increase respiration when PCO2 increases or pH
decreases
• Peripheral chemoreceptors
– Measure PO2 in arterial blood
– Increase respiration when PO2 <60 mm Hg
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Scenario
• You are caring for a COPD client
• He has chronically high PCO2
• He is being given low-flow oxygen and complains
all the time that he “needs more air,” so you turn
up his oxygen.
Question:
• When you check on him later, he is unconscious
and not breathing. What happened?
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