In diffuse alveolar damage (DAD), the exudative phase (days 1–7) is characterized by hyaline membrane formation. These hyaline membranes are composed of:
- A Surfactant protein A (SP-A) polymers precipitated by inflammation
- B Fibrin and plasma proteins admixed with necrotic epithelial debris ✓
- C Collagen I secreted by activated fibroblasts
- D Mucin secreted by hyperplastic type II pneumocytes
Explanation
Hyaline membranes in DAD (the histological pattern of ARDS) are composed of fibrin exudate admixed with plasma proteins (including complement, albumin) and the necrotic cellular debris of type I pneumocytes lining the alveolar walls. They form a smooth, eosinophilic, glassy lining along the alveolar walls and ducts. The fibrin derives from vascular leakage of plasma proteins through damaged endothelium, and the cellular debris represents dead type I alveolar epithelial cells (which cover 95% of alveolar surface). In the organizing (proliferative) phase (days 7–21), type II pneumocytes proliferate to replace damaged type I cells and myofibroblasts deposit collagen.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.