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Histology of the Respiratory System

• Trachea:

  • Contains C-shaped hyaline cartilage supporting the airway.
  • Lined with respiratory epithelium (ciliated pseudostratified columnar with goblet cells).
  • Submucosa contains seromucous glands.
  • Fibromuscular membrane contains trachealis muscle.
  • Adventitia layer surrounds the trachea.

• Trachealis:

  • Muscular tissue in the trachea wall.

• Trachea Mucosa:

  • Epithelium containing goblet cells.
  • Basal lamina.
  • Lamina propria.

• Trachea Submucosa:

  • Blood vessels.
  • Connective tissue.

• Trachea Cartilage:

  • Hyaline cartilage, appears basophilic, rich in sulfated GAGs and eosinophilic collagen.
  • Perichondrium (thicker towards the adventitia).

• Oblique Sections:

  • Oblique sections of trachea tissue can show multiple cartilages in a single plane.

• Bronchi:

  • Classified as extrapulmonary (e.g., primary and secondary) or intrapulmonary (e.g., tertiary to terminal).
  • Extra-pulmonary bronchi are not surrounded by lung tissue.
  • Intrapulmonary bronchi are surrounded by lung tissue.
  • Contain cartilage plates, decreasing in size as they branch down.
  • Lined with respiratory epithelium.
  • Submucosa contains glands.

• Bronchioles:

  • Lack cartilage and submucosal glands.
  • Have smooth muscle.
  • Lined with simple columnar epithelium. -Transition to simple cuboidal epithelium at the terminal bronchioles.
  • Branching terminal bronchioles form respiratory bronchioles.

• Respiratory Bronchioles:

  • Characterized by a transition from smooth muscle-dominated walls to alveolar structures.

• Alveolar Ducts and Alveoli:

  • Alveolar ducts lead to alveoli, the terminal air sacs.
  • Alveoli are lined with a simple squamous epithelium (type I pneumocytes).

• Alveoli:

  • Contain alveolar type II cells (surfactant producing cells).
  • Surrounded by capillary networks for gas exchange.

• Pulmonary Artery:

  • Present in lung tissue images; often in relation to bronchioles and alveoli.

• Alveolar Septa:

  • The thin walls of the alveoli, separating adjacent alveoli.

• Club/Clara cells:

  • Found in the epithelium of bronchioles, producing surfactant.

• Important Note:

  • The epithelium of alveoli, alveolar sacs, and ducts are predominantly simple squamous, mainly constituted by type I pneumocytes.

• Histology of Vessels

  • Artery, vein, and blood vessels were observed in relation to broncho-pulmonary structures.