Type II pneumocytes (alveolar epithelial cells) are the progenitor cells of the alveolar epithelium. Which specific histological feature on electron microscopy identifies Type II pneumocytes?
- A Caveolae and pinocytic vesicles in the attenuated squamous cytoplasm for gas exchange
- B Osmiophilic lamellar bodies (multilamellar membrane-bound organelles storing surfactant phospholipids) within the cuboidal cell cytoplasm ✓
- C Cytoplasmic granules containing Clara cell secretory protein (CC16/CCSP)
- D Electron-dense core vesicles containing catecholamines within Kulchitsky (neuroendocrine) cells
Explanation
Type II pneumocytes (granular pneumocytes) are cuboidal cells that synthesise and secrete pulmonary surfactant. Their hallmark ultrastructural feature is osmiophilic (electron-dense) lamellar bodies — membrane-bound, concentrically lamellated organelles that store surfactant phospholipids (principally dipalmitoylphosphatidylcholine). Lamellar bodies are secreted by exocytosis into the alveolar space, where they unravel into tubular myelin and eventually form the surfactant film. Type I pneumocytes are flattened squamous cells with caveolae for transcytosis. Clara (club) cells secrete CC16 and are found in terminal bronchioles. Kulchitsky cells are neuroendocrine cells of the bronchial mucosa.
Reference: BD Chaurasia's Human Anatomy, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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