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Lung Anatomy: Lobes, Pleura, Airways, Alveoli, and Vasculature

Gross & Microscopic Structure

Lobes & Fissures

  • Right lung: 3 lobes (upper, middle, lower) separated by oblique and horizontal fissures.
  • Left lung: 2 lobes (upper, lower) separated by oblique fissure; lingula = homologue of middle lobe.

Pleura

  • Visceral pleura: Invests lung surface; insensitive.
  • Parietal pleura: Lines thoracic cavity; sensitive (somatic innervation).
  • Pleural space: Potential space with ~10–20 mL serous fluid; negative pressure (−5 cmH₂O) maintains lung expansion.

Airway Tree

Trachea → main bronchi → lobar bronchi (3R, 2L) → segmental bronchi (10R, 8–10L) → subsegmental → bronchioles (no cartilage) → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveoli (gas exchange units).

Alveoli & Gas Exchange

  • ~300–500 million alveoli; total surface area ~70–100 m².
  • Type I pneumocytes (95% surface, thin for diffusion); Type II (surfactant production).
  • Dense capillary network; blood-gas barrier ~0.5 μm.

Vasculature

  • Pulmonary arteries: Deoxygenated blood from RV; low pressure (15/8 mmHg).
  • Pulmonary veins: Oxygenated blood to LA (4 veins).
  • Bronchial arteries: Systemic supply to airways/tissue (from thoracic aorta).

Lymphatics & Nerves

  • Deep (peribronchial) and superficial (subpleural) plexuses → hilar/mediastinal nodes.
  • Autonomic: Parasympathetic (vagus) → bronchoconstriction/secretion; Sympathetic → bronchodilation.

Color

Healthy: pink-gray. Anthracotic pigmentation (carbon) with age/pollution/smoking.

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