In-Depth Notes on Mechanisms of Pulmonary Disease

Anatomy of the Respiratory Tract

  • Upper airway:
    • Composed of the mouth, nose, pharynx, and larynx, covered by mucosa.
  • Lower airway:
    • Trachea: Comprised of columnar epithelial cells, goblet cells, and cilia.
    • Bronchi: Pseudostratified columnar epithelium with goblet cells, cilia, smooth muscle, and connective tissue.
    • Bronchioles: Consist of columnar cuboidal epithelium with sparse goblet and cilia.

Alveoli and Gas Exchange

  • Acinus structure:
    • Respiratory bronchioles: Thin epithelium with minimal smooth muscle/connective tissue.
    • Alveolar ducts lead to alveoli, which are the gas exchange units of the lungs.
    • Alveoli consist of an epithelial layer and thin basement membrane.
    • Type I cells: Structural cells.
    • Type II cells: Responsible for surfactant production.

Respiratory Muscles

  • Major breathing muscles:
    • Diaphragm: Primary muscle for inhalation.
    • Accessory muscles of inhalation:
    • External intercostals.
    • Sternocleidomastoid.
    • Accessory muscles of exhalation:
    • Internal intercostals.
    • Abdominal muscles.

Lung Functions and Gas Exchange

  • Essential functions:

    • Moves O2O_2 into the blood.
    • Removes CO2CO_2 from the blood.
    • Warms and humidifies air, traps inhaled particles.

  • Capillary network: Low-pressure system, where at resting conditions only 25% of pulmonary capillaries are perfused.

  • Fluid balance: Critical factors include hydrostatic pressure, colloid osmotic pressure, and capillary permeability.

    • Increased hydrostatic pressure results in fluid accumulation in the interstitium.

Lung Compliance

  • Describes how easily the lungs can be inflated. Factors include:
    • Presence of elastin and collagen fibers.
    • Water content in the lungs.
    • Surface tension from surfactants.

Alterations in Pulmonary Function

  • Hypoventilation causes:
    • CNS depressants, obesity, obstructive sleep apnea (OSA), myasthenia gravis, chest wall damage.
  • Hyperventilation causes:
    • Fever, pain, anxiety, less commonly sepsis and brainstem injuries.

Lung Volumes and Capacities

  • Key volumes include:
    • Tidal Volume: Volume of air inhaled or exhaled in a normal breath.
    • Inspiratory Reserve Volume: Maximum volume of air that can be inhaled after a normal inspiration.
    • Expiratory Reserve Volume: Maximum volume of air that can be exhaled after a normal expiration.
    • Residual Volume: Air remaining in the lungs after maximum exhalation.
    • Vital Capacity: Total volume of air that can be exhaled after a maximum inhalation.
    • Total Lung Capacity: Maximum volume of air in the lungs after a maximum inhalation.

Respiratory Pathologies

  • Ventilation-Perfusion (V/Q Mismatch):

    • Blood flows to lung areas without sufficient O2O_2, leading to decreased oxygenation.

  • Asthma:

    • Characterized by airway inflammation, hyper-responsiveness, and increased mucus causing obstruction.
    • Reversible obstruction.

  • Chronic Obstructive Pulmonary Disease (COPD):

    • Emphasizes either chronic bronchitis ("blue bloater") or emphysema ("pink puffer").
    • Resulting from exposure to harmful particles (especially cigarette smoke).

Cystic Fibrosis

  • An autosomal recessive disease characterized by dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) resulting in thick, sticky mucus that obstructs airways and causes respiratory infections.

  • Clinical findings include:

    • Chronic cough, difficulty breathing, malabsorption, and growth failure.

  • Diagnostics/Tests: Sweat chloride test, CF mutation identification, and pulmonary function tests.

Diagnosing and Treating Respiratory Diseases

  • Key diagnostic tests:
    • Chest X-rays, blood cultures, sputum cultures, and pulmonary function tests.
  • Common treatments:
    • Oxygen therapy, bronchodilators, antibiotics, and supportive care.