Mechanism of Bruise
Increased distress to tissue causes capillaries to break under the skin, allowing blood to escape and build up. As time progresses, blood seeps into the surrounding tissues, causing the bruise to darken and spread. Nerve endings within the affected tissue detect the increased pressure, which, depending on severity and location, may be perceived as pain or pressure or be asymptomatic. The damaged capillary endothelium releases endothelin, a hormone that causes narrowing of the blood vessel to minimize bleeding. As the endothelium is destroyed, the underlying von Willebrand factor is exposed and initiates coagulation, which creates a temporary clot to plug the wound and eventually leads to restoration of normal tissue.
During this time, larger bruises may change color due to the breakdown of hemoglobin from within escaped red blood cells in the extracellular space. The striking colors of a bruise are caused by the phagocytosis and sequential degradation of hemoglobin to biliverdin to bilirubin to hemosiderin, with hemoglobin itself producing a red-blue color, biliverdin producing a green color, bilirubin producing a yellow color, and hemosiderin producing a golden-brown color. As these products are cleared from the area, the bruise disappears. Often the underlying tissue damage has been repaired long before this process is complete.
Read more about this topic: Bruise
Famous quotes containing the words mechanism of, mechanism and/or bruise:
“A mechanism of some kind stands between us and almost every act of our lives.”
—Sarah Patton Boyle, U.S. civil rights activist and author. The Desegregated Heart, part 3, ch. 2 (1962)
“The two elements the traveler first captures in the big city are extrahuman architecture and furious rhythm. Geometry and anguish. At first glance, the rhythm may be confused with gaiety, but when you look more closely at the mechanism of social life and the painful slavery of both men and machines, you see that it is nothing but a kind of typical, empty anguish that makes even crime and gangs forgivable means of escape.”
—Federico García Lorca (1898–1936)
“Ah, little road, brown as my race is brown,
Your trodden beauty like our trodden pride,
Dust of the dust, they must not bruise you down.
Rise to one brimming golden, spilling cry!”
—Helene Johnson (b. 1907)