Blood is carried around the body in a transport system of arteries, capillaries and veins, and any damage to this network results in bleeding. Bleeding can be both external and internal. External bleeding involves a break to the skin surface, known as a wound, which can take many different forms. Internal bleeding is bleeding that occurs inside the body when there is no external injury for the blood to escape from. The most common form of internal bleeding is a small bruise from a minor impact. Heavy impact from car accidents, fights or falls, for example, can lead to serious internal bleeding, which may kill.
Transport of blood
Arteries have thick muscular walls, which contract. This pushes blood out from the heart under pressure. The blood contained within them is full of oxygen, which has been collected from the lungs, and the main function of the arteries is to take this oxygen-rich blood to the organs and body tissue. Because the blood is under pressure, and is so full of oxygen, arterial bleeding is characterised by bright red blood pumping from an injury. Arterial bleeding is very serious as blood is rapidly lost.
Veins have thin walls and return blood from the organs and tissues to the heart. They do not have muscles of their own and rely on the actions of the muscles around them to squeeze the blood around. To keep the blood moving in one direction around the body, they have a series of one-way valves that ensure a one-way flow. When these valves deteriorate, blood pools up in the veins making them swell up. This weakens the vein wall, resulting in a condition known as varicose veins. While the blood loss from a bleeding vein does not tend to be as quick as an arterial bleed, it does nonetheless have the potential to be a very serious and even fatal injury. Bleeding from a vein will seem to flow from an injury and as it has little or no oxygen it will appear to be a dark red.
Capillaries are very thin-walled vessels. Blood is forced through them under pressure, causing the food and oxygen stored in the blood to be pushed out into the body tissues and organs.
Types of injury
Small bleeds are very common and rarely need much treatment. Large blood loss may lead, if untreated, to shock and, potentially, death.
IncisionsClean and deep cuts characterised by paper cuts and knives are known as incisions. While these wounds do not tend to bleed a lot, there may be underlying damage to tendons and other tissues.Lacerations are jagged wounds, which tend to bieed a lot.
Puncture wounds are, as their name suggests, deep injuries caused by a long object such as a knitting needle. They do not tend to bleed a great deal but they carry the risk of infection as dirt can be carried a long way into the tissue. There is also a greater risk of damage to vital organs such as the lungs or liver.
Grazes are a commonplace injury and involve damage to the top layers of the skin. They do not cause major blood loss but are often dirty, as grazes tend to have debris embedded within them.
How does the body stop bleeding?
When a blood vessel is torn or cut, a series of chemical reactions takes place that causes the formation of a blood clot to seal the injury. Components of the blood known as platelets clump together at the injury site. Damaged tissue and platelets release chemicals that activate proteins called clotting factors. These react with a special protein (fibrinogen) to form a mesh of filaments that traps blood cells. These form the basis of a blood clot that contains white blood cells to help fight infection and specialised blood cells that help promote repair and recovery. A scab will form to protect the wound until repair has taken place. When applying pressure to the site of a wound you are helping the clotting process.
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