Loss of blood from the circulatory system caused by damage to the blood vessels or by a bleeding disorder. Bleeding may be visible (external) or concealed (internal). Rapid loss of more than 10 per cent of the blood volume can cause symptoms of shock, with fainting, pallor, and sweating. The speed with which blood flows from a cut depends on the type of blood vessel damaged: blood usually oozes from a capillary, flows from a vein, and spurts from an artery. If an injury does not break open the skin, blood collects around the damaged blood vessels close under the skin to form a bruise. Any lost blood that mixes with other body fluids such as sputum (phlegm) or urine will be noticed quite readily; bleeding in the digestive tract may make vomit or faeces appear darker than usual. Internal bleeding may not be discovered until severe anaemia develops.


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