Here is an example of a contusion to the arm. The blunt force injury ruptures small blood vessels in dermis and underlying soft tissue, resulting in extravasation of red blood cells. Initially, the contusion appears dull red to blue, but over time the red cells are broken down, releasing bilirubin and heme (which is processed by macrophages to hemosiderin), to give the yellow-brown hue seen here after a week.

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