There are between five and seven litres of blood in the average adult body. Blood is moved around the body under pressure by the cardiovascular system - the heart and blood vessels. Without an adequate blood volume and pressure, the human body soon collapses. Bleeding, or haemorrhage , poses a threat by causing both the volume and the pressure of the blood within the body to decrease through blood loss.
Serious wounds involve damage to blood vessels.
As arteries carry oxygenated blood from the heart, damage to a vessel is characterised by bright red blood which 'spurts' with each heartbeat. Damage to veins appears as a darker red flow. Capillary damage is associated with wounds close to the skin and is of a bright red 'ooze' from below the surface. Abrasion is a wound where the skin layers have been scraped off. Puncture wounds are perforations, and may be due to anything from a corkscrew to a bullet.