7th February 2024

Summary

Functions of the lung can be considered in terms of respiratory and non-respiratory functions.

The lung’s respiratory function involves exchanging oxygen and carbon dioxide. The lung’s respiratory function depends on ventilation, pulmonary circulation, diffusion of gases across the blood-gas barrier, and control mechanism of ventilation.

Non-respiratory function of the lung can be categorised into:

• Pulmonary circulation
  • Reservoir of blood in haemorrhage (around 400-500mL an adult)
  • Filters blood (removal of thrombi)
• Metabolic functions:
  • Metabolism of vasoactive substances
    • The site of activity is the pulmonary endothelium.
    • Examples:
      • Peptides (e.g. angiotensin I activated into angiotensin II, inactivation of bradykinin)
      • Amines (e.g. removal of serotonin and noradrenaline)
  • Synthesis of glycolipids (e.g. surfactant), proteins (collagen and elastin)
  • Catabolic functions (removal of proteases, e.g. alpha-1-antitrypsin)
  • Carbohydrate metabolism
• Immune functions
  • Physical filtration and removal of inhaled particles involving airway lining and mucociliary clearance, and airway reflexes (cough, sneeze)
  • Immunological defence against inhaled particles involving tonsils alveolar macrophages.
  • Secretion of immunoglobulin, primarily IgA, that is present in bronchial secretions.
• Acid-base balance
  • Via excretion of carbon dioxide and thus indirectly altering H+ concentration via the Henderson-Hasselbalch equation
• Drug absorption
  • Aerosolised inhaled drugs may rapidly pass into systemic circulation and have systemic effects (e.g. beta-agonists used as bronchodilators)
• Temperature regulation of the body