Chapter 21
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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Question
Which serous membrane lines the thoracic cavity?
a. Viscera pleura
b. Parietal pleura
c. Visceral mediastinum
d. Parietal mediastinum
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Answer
b. Parietal pleura
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
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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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 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
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 4 Oxygen Molecules
• 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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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
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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