MH 139 Lung

Lung

The lung consists of airways and structures for gas exchange.

The trachea divides into a primary bronchi for each lung. They divide into secondary (lobar) bronchi and then into segmental (terminal) bronchi.

• Primary Bronchi (#1,#2,#3)
  • Respiratory Epithelium - composed of a pseudostratified columnar epithelium.
  • Basement Membrane - thick, eosinophilic band beneath the epithelium.
  • Lamina Propria - dense irregular connective tissue.
    • Bronchial Cartilage - consists of hyaline cartilage.
    • Sero-Mucous Glands
    • Smooth Muscle
• Primary (Muscular) Bronchioles (#1,#2)
  • Epithelium changes from pseudostratified columnar to simple, ciliated columnar epithelium as they decrease in diameter.
  • Club Cells - dome-shaped secretory cells.
  • Smooth Muscle - variable amounts present.
• Terminal Bronchioles (#1,#2) - conducting airways.
  • Epithelium changes from simple, ciliated columnar epithelium to cuboidal epithelium.
  • Club Cells - become more prominent.
  • Smooth Muscle - variable amounts present.

• Respiratory Bronchioles (#1,#2,#3) - mixture of conducting epithelium and alveoli where respiration occurs.
  • Epithelium is a mixture of simple columnar and simple cuboidal epithelia.
  • Club Cells - become more prominent.
  • Smooth Muscle - only small amounts are present.
• Alveolar Ducts (#1,#2)- arise from respiratory bronchioles and are passageways lined with alveoli.
• Alveolar Sacs - spherical-like spaces with openings into multiple alveoli.
• Alveoli (#1,#2) - blind ending sacs that are the final termination of the airways.
  • Simple Epithelium (#1,#2,#3) - contains two types of pneumocytes resting on a thin basal lamina.
    • Type I - flattened, simple squamous epithelial cells.
      • Gas exchange occurs through these cells.
    • Type II - dome-shaped, cuboidal epithelial cells that project into the lumen.
      • Secrete surfactant that covers the alveolar surface and reduces surface tension.
  • Capillaries - dense network surround alveoli.
  • Smooth Muscle - often found at the ends of alveolar walls.