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| English: A comparison between human red blood cells differing in oxygenation state. The cell on the left presents an oxygenated appearance as it would while in arterial circulation (after loading oxygen and unloading carbon dioxide in the lungs). The cell on the right appears as it would when deoxygenated, or in venous circulation (after unloading oxygen and loading carbon dioxide in the oxygen requiring-tissue capillaries). (Photo credit: Wikipedia) |
All over your body,you have tiny blood vessels called capillaries. They get rupture when you have a wound.This causes blood to seep into tissues, and red cells break Hemoglobin the substance that gives red cells its colour, turns blue when oxygen is removed. Tissues quickly use up the oxygen in hemoglobin but hemoglobin does not get any resupply of oxygen as the blood vessels are broken.This is why a bruise gets a bluish colour. It looks even bluer if the overlying tissue is pink. In about 14 days the red-blood cells degenerate and are reabsorbed.Then the bruise disappears.
