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Structure and Function of the
Pulmonary System

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Structures of the Pulmonary
System
 Airways
 Pulmonary circulation
 Chest wall
 Lungs
 Lobes (three on right, two on left)
 Segments
 Lobules
 Mediastinum

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Structures of the Pulmonary
System (cont’d)

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Structures of the Pulmonary
System (cont’d)
 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 (cont’d)

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Structures of the Pulmonary
System (cont’d)
 Gas-exchange airways:
 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 (cont’d)

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Structures of the Pulmonary
System (cont’d)

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Pulmonary and Bronchial
Circulation
 Pulmonary circulation has a lower
pressure than the systemic circulation
 One-third of pulmonary vessels are filled
with blood at any given time
 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 (cont’d)
 Alveolocapillary membrane
 Formed by the shared alveolar and capillary
walls
 Gas exchange occurs across this membrane
 Pulmonary veins
 Each drains several pulmonary capillaries
 Dispersed randomly throughout the lung
 Leave the lung at the hila and enter the left
atrium

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Pulmonary and Bronchial
Circulation (cont’d)

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Chest Wall and Pleura
 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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Thoracic Cavity

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Function of the Pulmonary System
 Ventilate the alveoli
 Diffuse gases into and out of the blood
 Perfuse the lungs so the body receives
oxygen

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Function of the Pulmonary System
(cont’d)
 Ventilation
 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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Ventilation
 Respiratory center
• Dorsal respiratory
group
• Ventral respiratory
group
• Pneumotaxic center
• Apneustic center
 Peripheral
chemoreceptors
 Lung receptors:
• Irritant receptors
• Stretch receptors
• J receptors
 Chemoreceptors:
• Central
chemoreceptors
• Peripheral
chemoreceptors
 Neurochemical control

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Neurochemical Respiratory Control

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Mechanics of Breathing
 Major and accessory muscles:
 Major muscles of inspiration:
• Diaphragm
• External intercostals
 Accessory muscles of inspiration:
• Sternocleidomastoid muscle
• Scalene muscles
 Accessory muscles of expiration:
• Abdominal intercostal muscles
• Internal intercostal muscles

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Muscles of Ventilation

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Mechanics of Breathing
 Alveolar surface tension and ventilation
 Function of surfactant
 Elastic properties of the lung and chest
wall:
 Elastic recoil
 Compliance
 Airway resistance
 Work of breathing

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Mechanics of Breathing
(cont’d)

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Gas Transport
 Four steps
 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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Measurement of Gas Pressure
 Barometric pressure
 Partial pressure
 Partial pressure of water vapor

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Measurement of Gas Pressure
(cont’d)

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Gas Transport
 Distribution of ventilation and perfusion
 Gravity and alveolar pressure
 Ventilation-perfusion ratio

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Gas Transport (cont’d)
 Oxygen transport
 Diffusion across the alveolocapillary membrane
 Determinants of arterial oxygenation:
• Hemoglobin binding
• Oxygen saturation
 Oxyhemoglobin association and dissociation
• Oxyhemoglobin dissociation curve
• Bohr effect

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Measurement of Gas Pressure

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Gas Transport
 Carbon dioxide transport
 Dissolved in plasma
 Bicarbonate
 Carbamino compounds
 Haldane effect

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Control of Pulmonary Circulation
 Hypoxic pulmonary vasoconstriction
 Caused by low alveolar paO2
 Blood is shunted to other, well-ventilated
portions of the lungs
• Provides better ventilation and perfusion matching
• If hypoxia affects all segments of the lungs, the
vasoconstriction can result in pulmonary
hypertension

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Control of Pulmonary Circulation
(cont’d)
 Acidemia also causes pulmonary artery
constriction

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Tests of Pulmonary Function
 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
 Loss of elastic recoil
 Stiffening of the chest wall
 Alterations in gas exchange
 Increases in flow resistance
 Decreased exercise tolerance

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Aging and the Pulmonary System
(cont’d)