An abdominal aortic aneurysm (AAA) is most commonly located infrarenally. The predominant mechanism of aneurysm expansion involves:
- A Destruction of medial elastin and collagen by matrix metalloproteinases (MMPs) secreted by macrophages and neutrophils ✓
- B Smooth muscle hypertrophy and medial hyperplasia
- C Intimal proliferation from shear stress compressing the media
- D Fibrosis of the adventitia restricting compensatory remodeling
Correct answer: A. Destruction of medial elastin and collagen by matrix metalloproteinases (MMPs) secreted by macrophages and neutrophils
Explanation
AAA pathogenesis involves chronic transmural inflammation with macrophage and neutrophil infiltration of the media and adventitia, secreting MMPs (especially MMP-9/gelatinase B and MMP-2) that degrade medial elastin and collagen. Loss of structural proteins allows progressive dilation under arterial pressure. The infrarenal aorta has fewer vasa vasorum, making it more susceptible. Atherosclerosis contributes by impairing nutrient delivery to the media.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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