MHS 205 Lung

Lung

The lung consists of airways and structures for gas exchange.

The trachea divides into a primary bronchi for each lung. The smaller intrapulmonary airways are devoid of cartilage and glands in their walls.

• Primary (Muscular) Bronchioles (not present in this specimen)
  • Epithelium changes from pseudostratified columnar to simple, ciliated columnar epithelium as they decrease in diameter.
  • Club Cells - dome-shaped secretory cells with short microvilli. (Do not have cilia.)
  • Smooth Muscle - variable amounts present.
• Terminal Bronchioles - conducting airways.
  • Epithelium changes from simple, ciliated columnar epithelium to cuboidal epithelium.
  • Club Cells - become more prominent.
  • Smooth Muscle - variable amounts present.
• Respiratory Bronchioles - 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 - arise from respiratory bronchioles and are passageways lined with alveoli and occasional regions of simple cuboidal epithelium.
• Alveolar Sacs - spherical-like spaces with openings into multiple alveoli.
• Alveoli - blind ending sacs that are the final termination of the airways.
  • Simple Epithelium (#1, #2 and #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.
  • Macrophages (or Dust Cells) (#1 and #2) - large, dark cells within alveoli that engulf dust particles, bacteria, and other pathogens.
  • Capillaries - dense network surround alveoli.
  • Smooth Muscle - often found at the ends of alveolar walls.