Respiratory System MCAT Practice Question
A 68-year-old man with a 45-pack-year smoking history presents with progressive dyspnea on exertion, chronic cough, and weight loss over the past 2 years. Pulmonary function testing shows FEV1 of 35% predicted and a markedly elevated functional residual capacity (FRC). High-resolution CT of the chest demonstrates basilar-predominant emphysema with loss of normal lung architecture. Laboratory analysis of his bronchoalveolar lavage fluid reveals significantly elevated neutrophil elastase activity. Compared to age-matched controls, his lungs demonstrate reduced elastic recoil on pressure-volume curve analysis. Which of the following best explains the mechanism by which increased elastase activity results in decreased elastic recoil in this patient's lungs?
Answer choices
- AElastase proteolytically cleaves the backbone of elastin molecules, disrupting the cross-linked fiber network responsible for elastic propertiesCorrect answer
- BElastase phosphorylates elastin at lysine residues, preventing the formation of desmosine and isodesmosine cross-links
- CElastase inhibits lysyl oxidase in lung fibroblasts, preventing hydroxylation of lysine residues required for elastin cross-linking
- DElastase degrades collagen type IV in the alveolar basement membrane, the primary structural component providing lung elasticity
- EElastase promotes excessive elastin synthesis and cross-linking, leading to increased lung stiffness and reduced compliance
- FElastase cleaves the signal peptide from tropoelastin, preventing its secretion and subsequent incorporation into the extracellular matrix
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