Physiological Adaptation Q 46
Atherosclerosis impedes coronary blood flow by which of the following mechanisms?
A. Plaques obstruct the vein
B. Plaques obstruct the artery
C. Blood clots form outside the vessel wall
D. Hardened vessels dilate to allow the blood to flow through
Correct Answer: B. Plaques obstruct the artery.
Arteries, not veins, supply the coronary arteries with oxygen and other nutrients. Atherosclerosis is a lipoprotein-driven disease that leads to plaque formation at specific sites of the arterial tree through intimal inflammation, necrosis, fibrosis, and calcification.
Option A: Atherosclerosis is a direct result of plaque formation in the artery. Most often, the culprit morphology is plaque rupture with exposure of highly thrombogenic, red cell-rich necrotic core material. The permissive structural requirement for this to occur is an extremely thin fibrous cap, and thus, ruptures occur mainly among lesions defined as thin-cap fibroatheromas.
Option C: Blood clots form inside the vessel wall and impede circulation. Also common are thrombi forming on lesions without rupture (plaque erosion), most often on pathological intimal thickening or fibroatheromas. However, the mechanisms involved in plaque erosion remain largely unknown, although coronary spasm is suspected.
Option D: Hardened vessels can’t dilate properly and, therefore, constrict blood flow. During atherogenesis, the local vessel segment tends to remodel in such a way that the lumen area is usually not compromised until plaques are large (expansive remodeling). Thereafter stenosis formation may occur through continued plaque growth or shrinkage of the local vessel segment (constrictive remodeling) or a combination of the 2 processes.