Within a thrombus, the dark lines of Zahn are attributed to_______________?
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Answer: D. Aggregated R.B.C
Explanation
The alternating pale and dark layers known as lines of Zahn in a thrombus are composed of aggregated platelets/fibrin and red blood cells respectively. Pulsatile blood flow in the heart or large arteries deposits platelets and fibrin during periods of rapid flow. Red blood cells settle and become trapped during slower flow phases, creating the contrasting dark layers. Lines of Zahn are macroscopic and microscopic laminations found exclusively in thrombi formed within flowing blood. Platelets and polymerized fibrin form the pale layers of the characteristic laminar thrombus structure. Red blood cells predominate in the intervening dark layers due to sedimentation under flowing conditions.
Option A is incorrect because coagulated fibrin alone does not account for the dark alternating erythrocyte bands. Option B is wrong since aggregated proteins do not form the distinct visible laminations of lines of Zahn. Option C is incorrect because aggregated platelets form the pale layers rather than the dark red cell layers.
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