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Respiratory system
L2
Faisal I. Mohammed, MD, PhD
University of Jordan
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Airflow
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Air pressure differences drive airflow
3 other factors affect rate of airflow and ease of pulmonary
ventilation
 Surface tension of alveolar fluid
 Causes alveoli to assume smallest possible diameter
 Accounts for 2/3 of lung elastic recoil
 Prevents collapse of alveoli at exhalation
 Lung compliance
 High compliance means lungs and chest wall expand easily
 Related to elasticity and surface tension
 Airway resistance
 Larger diameter airway has less resistance
 Regulated by diameter of bronchioles & smooth muscle
tone
University of Jordan
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Surfactant
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Complex mixture of phospholipids, proteins, ions
Produced by type II alveolar epithelial cells
It reduces surface tension forces by forming a monomolecular
layer between aqueous fluid lining alveoli and air, preventing a
air/water interface
Function
 Reduces surface tension
 Prevents alveolar collapse
 Increases compliance
 Reduces work of breathing
However, the high surface tension and collapse of the alveoli
is prevented by surfactant.
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Compliance
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Distensibility (stretchability):
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Ease with which the lungs can expand.
Change in lung volume per change in
transpulmonary pressure.
DV/DP
100 x more distensible than a balloon.
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Compliance is reduced by factors that produce
resistance to distension.
Lung volumes and capacities
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Minute ventilation (MV) = total volume of air inhaled and
exhaled each minute
Normal healthy adult averages 12 breaths per minute
moving about 500 ml of air in and out of lungs (tidal
volume)
MV = 12 breaths/min x 500 ml/ breath = 6 liters/ min
Alveolar ventilation = (tidal volume – dead space)*
respiratory rate
e.g Alveolar ventilation = (500-150)*12= 4.2 liters/min
University of Jordan
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Spirometer
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Lung volumes and capacities
Spirometer - measurement of lung volumes
- measurement of the oxygen consumption
Spirogram of Lung Volumes and Capacities
University of Jordan
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Restrictive and Obstructive Disorders
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Restrictive disorder:
 Vital capacity is
reduced.
 FVC is normal.
Obstructive disorder:
 Diagnosed by tests
that measure the
rate of expiration.
 VC is normal.
 FEV1 is < 80%.
Insert fig. 16.17
Lung Volumes
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Only about 70% of tidal volume reaches respiratory
zone
Other 30% remains in conducting zone
Anatomic (respiratory) dead space – conducting
airways with air that does not undergo respiratory gas
exchange
Alveolar ventilation rate – volume of air per minute
that actually reaches respiratory zone
Inspiratory reserve volume – taking a very deep
breath
University of Jordan
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Lung Volumes
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Expiratory reserve volume – inhale normally and
exhale forcefully
Residual volume – air remaining after expiratory
reserve volume exhaled
Vital capacity = inspiratory reserve volume +
tidal volume + expiratory reserve volume
Total lung capacity = vital capacity + residual
volume
University of Jordan
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Thank You
University of Jordan
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