Structure and Function of the Pulmonary System

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Structure and Function of the Pulmonary System

• Chapter 32

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Structures of the Pulmonary System

• 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
• 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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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
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Pulmonary and Bronchial Circulation

• Alveolocapillary membrane
• Formed by the 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

• 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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Function of the Pulmonary System

• 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

• Neurochemical control
• Respiratory center
• Dorsal respiratory group
• Ventral respiratory group
• Pneumotaxic center
• Apneustic center
• Peripheral chemoreceptors

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Ventilation

• Neurochemical control
• Lung receptors
• Irritant receptors
• Stretch receptors
• J-receptors
• Chemoreceptors
• Central chemoreceptors
• Peripheral chemoreceptors

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Mechanics of Breathing

• Major and accessory muscles
• 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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Mechanics of Breathing

• Alveolar surface tension
• 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
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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

• 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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Gas Transport

• Distribution of ventilation and perfusion
• Gravity and alveolar pressure
• Ventilation-perfusion ratio

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Measurement of Gas Pressure
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Gas Transport

• Oxygen transport
• Diffusion across the alveolocapillary membrane
• Determinants of arterial oxygenation
• Oxyhemoglobin association and dissociation
• Oxyhemoglobin dissociation curve

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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 vasoconstriction
• Caused by low alveolar pO2
• 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
• 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

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Aging and the Pulmonary System