Summary of possible structural and functional changes in the small airways of asthmatics
| Structural changes | Functional changes | |
| Epithelium | Variation in thickness Altered epithelial cell to cell adhesion Goblet cell hyper/metaplasia Mucus accumulation/plugging Alterations in expression of MUC5AC | Impaired barrier function Increased mucus production Epithelial–mesenchymal transition |
| ECM | ||
| Inner airway wall area | Changes in ECM composition Basement membrane thickening | Altered ECM production Stiffening of the airways Increased ASM opposing force |
| Within ASM | Changes in ECM composition | Altered ECM production Stiffening of the airways |
| Outer airway wall area | Changes in ECM composition Outer airway wall area thickening | Altered ECM production Stiffening of the airways Increased ASM opposing force Decreased force transduction |
| ASM | Thickening of ASM layer ASM hyperplasia/hypertrophy | Increased contractile force Length adaptation Force adaptation Increased maximal shortening Increased shortening velocity Impaired bronchodilating and protective effect after a deep inspiration |
| Parenchyma | Abnormal airway alveolar attachments | Decreased force transduction Decreased parenchymal tethering force |
ECM: extracellular matrix; ASM: airway smooth muscle.