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Anatomy of the lungs. Shown are the five lobes of the lung and the anatomy of the tracheobronchial tree.


  • Mechanics:

    • - Statics refer to forces acting on the lung that affect volumes and elastic behavior

      • Lungs = collapsing forces; chest wall (CW) = expanding forces (Figure 2.2)

    • - Dynamics refer to the forces moving air, including flow patterns and resistance

  • Gas exchange: Handling of O2/CO2


The lung–chest wall system. The chest wall has a tendency toward expansion, while the lungs have a tendency toward collapse. At the end of a normal exhalation, the volume of air remaining in the lungs is the functional reserve capacity. While at the functional reserve capacity, the expanding chest wall forces and the collapsing lung forces are in balance. Since initiating a new breath requires the lung–chest wall system to shift away from this equilibrium point, inhalation is an active process that requires the use of the respiratory muscles.


  • Volumes and Capacities:

    • - Definitions (Table 2.1)

    • - Changes in pathologic states (Figure 2.3)

      • Obstructive lung disease (e.g., asthma, emphysema): ↑TLC, FRC, RV; ↓↓FEV1, ↓FVC, FEV1/FVC < 0.7

      • Restrictive lung disease (e.g., fibrosis): ↓TLC, FRC, RV; ↓FEV1, ↓↓FVC, ↑ or normal FEV1/FVC

  • Compliance: C = ΔVP

    V = volume, P = pressure

    • - Compliance = Filling term; ability of lungs to stretch

    • - Elastance = Expiration term; ability of lungs to collapse from stretched position

    • - Obstructive diseases = ↑Compliance, ↓Elastance; Restrictive diseases = ↓Compliance, ↑Elastance

  • Surface tension: P = 2T/r

    P = pressure, T = surface tension, r = radius

    • - Law of Laplace: Large alveoli remain open due to high radius, and small alveoli collapse, causing atelectasis

    • - Surfactant:

      • Decreases surface tension → Decreases pressure → Increases compliance and reduces alveolar collapse

      • Produced by Type II alveolar cells: Choline + diacylglycerol → dipalmitoylphosphatidylcholine (DPPC)

      • Surfactant contains lecithin; if lecithin:sphingomyelin ratio ≥ 2:1 in amniotic fluid = lung maturity

    • - Hysteresis: Compliance (i.e., the slope of a pressure/volume curve) changes with inspiration and expiration; compliance is lower during expiration and at extreme volumes (i.e., very full lungs or very empty lungs)


Lung volumes and capacities in health and disease. A) The four components of volume in the lung: Tidal volume (TV), expiratory reserve volume (ERV), inspiratory reserve volume (IRV), and residual volume (RV), as well as capacities which are measurements of two or more volumes. Functional residual capacity (FRC) = ERV + RV. Inspiratory capacity (IC) = TV + IRV. Vital capacity (VC) = ...

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