Chapter 32
Structure and Function of the
Pulmonary System
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Structures of the
Pulmonary System
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

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Airways
Blood vessels
Chest wall
Lungs



Lobes
Segments
Lobules
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Structures of the Pulmonary System
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Structures of the
Pulmonary System

Conducting airways

Upper airways
• Nasopharynx
• Oropharynx
 Larynx
• Connects upper and lower airways
 Lower airways
• Trachea
• Bronchi
• Terminal bronchioles
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Structures of the Pulmonary System
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Structures of the
Pulmonary System

Gas-exchange airways
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

Respiratory bronchioles
Alveolar ducts
Alveoli
• Epithelial cells

Type I alveolar cells
– Alveolar structure

Type II alveolar cells
– Surfactant production
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Structures of the Pulmonary System
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Structures of the Pulmonary System
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Structures of the Pulmonary System
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Gas Exchange
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Alveoli


Primary gas-exchange units
Pores of Kohn
• Permit air to pass through the septa from alveolus to alveolus


Collateral ventilation and even air distribution
Lungs contain approximately 25 million alveoli at
birth and 300 million by adulthood
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Pulmonary and
Bronchial Circulation


Pulmonary circulation has a lower pressure
than systemic circulation (18 mmHg)
Only one third of vessels filled with blood at
any given time
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Pulmonary and
Bronchial Circulation
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
Pulmonary artery divides and enters the lung
at the hilus
Each bronchus and bronchiole has an
accompanying artery or arteriole
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Pulmonary and Bronchial
Circulation
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Pulmonary and
Bronchial Circulation

Alveolocapillary membrane


Formed by shared alveolar and capillary walls
Thin membrane of alveolar epithelium, the
alveolar basement membrane, interstitial space,
the capillary basement membrane, and the
capillary endothelium
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Pulmonary and Bronchial Circulation
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Chest Wall and Pleura
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Chest wall



Skin, ribs, and intercostal muscles
Thoracic cavity
Pleura




Serous membrane
Parietal and visceral layers
Pleural space (cavity)
Pleural fluid
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Lung Functions
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Gas exchange
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Supply oxygen
Eliminate CO2
Maintain pH
Eliminate water
Other functions

Maintain normal body temperature
 Immune responses
 Hormone secretion
 Metabolism
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Requirements for Ventilation,
Perfusion, and Diffusion
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

Adequate inspired O2 – (FiO2)
Ventilation and perfusion of alveoli
A permeable alveolocapillary membrane
Adequate blood flow
Ability to transport O2 and CO2
Ability of cell to use O2 and eliminate CO2
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Requirements for Ventilation,
Perfusion, and Diffusion

Adequate inspired O2 – (FiO2)
Barometric pressure is 760 at sea level
21% x 760 = partial pressure of O2 at sea level = ~160 mmHg
Barometric pressure is 600 at Salt Lake City
(much lower on Mt. Everest)
21% x 600 = partial pressure of O2 at SLC = ~126 mmHg
Why we give oxygen at high altitude
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Function of the Pulmonary
System
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Ventilation
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

Mechanical movement of gas or air into and out of
the lungs
Minute volume
• Ventilatory rate multiplied by the volume of air per breath
Alveolar ventilation
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Lung Volumes and Capacities
Based on Age, Gender, Height



Dead space: oropharynx to division 16 (about
equal to ideal body weight)
Tidal volume (per breath) 400-800 ml
IRV 3000 ml additional air that could be inhaled
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Lung Volumes and Capacities
Based on Age, Gender, Height

ERV 1000 ml remaining air



Forced vital capacity (theoretical)


Can be forcefully expired after normal expiration FEV1
Why abdominal thrusts work; expel TV plus ERV
TV + IRV + ERV ~4500-5000 ml
Residual volume constant ~1200 ml

Air remaining in alveoli
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Formulas
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Minute ventilation (or volume/min)
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


RR x TV
RR 16, TV 500
16 x 500 = 8000 ml/min
Effective minute volume: RR x (TV-DS)


100 lb, RR 16, TV 500 ml
16 (500-100) = 6400 ml/min
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Control of Ventilation

ANS
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Stimulates smooth muscle (contract relax)
• Airway lumen diameter
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Terms

Hypoxia
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
Low oxygen in the cell
Hypoxemia

Low oxygen in arterial blood (low O2 saturation)
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Control of Ventilation

Chemoreceptors
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Central receptors
• Reflects PaCO2
• Stimulated by H+ in cerebrospinal fluid (pH)
 Peripheral receptors
• Aorta and carotid bodies
• Stimulated by hypoxemia (PaO2)
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Control of Ventilation

Irritant receptors: epithelium of conducting
airways
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
Cough, bronchoconstriction, decrease RR
Stretch receptors: protective

Decrease RR and volume
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Ventilation

Neurochemical control
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
Respiratory center
• Dorsal respiratory group
• Ventral respiratory group
• Pneumotaxic center
• Apneustic center
Peripheral chemoreceptors
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Ventilation

Neurochemical control
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
Lung receptors
• Irritant receptors
• Stretch receptors
• J-receptors
Chemoreceptors
• Central chemoreceptors
• Peripheral chemoreceptors
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Mechanics of Breathing
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Major and accessory muscles
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Major muscles of inspiration
• Diaphragm
• External intercostals
Accessory muscles of inspiration
• Sternocleidomastoid and scalene muscles
Accessory muscles of expiration
• Abdominal and internal intercostal muscles
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Muscles of Ventilation
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Overview: Mechanics of Breathing
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Alveolar surface tension
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
Function of surfactant
Elastic properties of lung and chest wall
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Elastic recoil
 Compliance
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Airway resistance
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

Airway size
Gas velocity (Poiseuille’s law)
Muscular effort
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Mechanics of Breathing
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Surface Tension of Water


Tendency of water molecules to contract to the
smallest possible surface area (bead) with
exposure to air
Increased surface tension = increased work of
breathing
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Laplace’s Law


The smaller a sphere’s radius (alveoli) the
greater the surface tension and the more difficult
(work) to expand the alveoli
P = 2t/r

P = pressure inside a sphere (alveoli)
 t = surface tension
 r = radius of a sphere

Surfactant reduces fluid surface tension lining
the alveoli and decreases tendency to collapse,
preventing atelectasis
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Compliance



A measure of lung and chest wall distensibility or
“stiffness”
Volume ― volume of air moved
C=
Pressure ― force to move the air
Low: increased work of inspiration


Stiff lungs
High: increased work of expiration

Baggy lungs
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Measurement of Gas Pressure

Barometric pressure


Partial pressure
Partial pressure of water vapor
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Measurement of Gas Pressure
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Measurement of Gas Pressure
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Gas Transport
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Four steps
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
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Ventilation of the lungs
Diffusion of oxygen from the alveoli into the
capillary blood
Perfusion of systemic capillaries with oxygenated
blood
Diffusion of oxygen from systemic capillaries into
the cells
Diffusion of CO2 occurs in reverse order
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Gas Transport

Distribution of ventilation and perfusion


Gravity and alveolar pressure
Ventilation-perfusion ratio
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Gas Transport: O2
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Oxygen transport
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
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Diffusion across alveolocapillary membrane
Determinants of arterial oxygenation
Oxyhemoglobin association and dissociation
• Oxyhemoglobin dissociation curve
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Gas Transport: CO2

Carbon dioxide transport




Dissolved in plasma
Bicarbonate
Carbamino compounds
Haldane effect
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Measurement of Gas Pressure
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Measurement of Gas Pressure
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Clinical Manifestations: Hypoxemia

Early

Tachycardia
 Mild increase in blood pressure
 Diaphoresis (stress response)
 Confusion (CNS response)
 Loss of judgment
 Cyanosis after 5 g desaturation

Late


Stupor
Decreased BP, myocardium not getting enough O2
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Control of Pulmonary Circulation

Hypoxic vasoconstriction
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
Caused by low alveolar PO2
Blood is shunted to other, well-ventilated portions
of the lungs
• Better ventilation and perfusion matching
• If hypoxia affects all segments of lungs, the
vasoconstriction can result in pulmonary hypertension

Acidemia also causes pulmonary artery
constriction
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Tests of Pulmonary Function
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Spirometry
Diffusion capacity
Residual volume
Functional reserve capacity (FRC)
Total lung capacity
Arterial blood gas analysis
Chest radiographs
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Aging and the Pulmonary System
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
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Loss of elastic recoil
Stiffening of the chest wall
Alterations in gas exchange
Increases in flow resistance
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Aging and the Pulmonary System
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