How Inflammation Occurs
Red Painful Swelling is Unpleasant but Necessary for Life
Inflammation is by its very nature unpleasant but it is the the body's first major defense against infection.
Everybody has some experience of inflammation. It might be a sore throat, the swelling around a wound, an insect bite or the painful swelling around an injured joint. It's often the thing we notice most about an illness or injury, the red, swollen and painful bit. Inflammation is usually very unpleasant, occasionally dangerous and essential for life.
Celsus in AD35 gave the classic description of inflammation: red, hot, swollen and tender. It's the usual reaction to injury. Inflammation is clearly a very important mechanism for the body since it occurs so frequently even though very occasionally it can be dangerous – severe swelling in the throat can lead to asphyxiation. The point about inflammation is that it's our first defense mechanism against micro-organisms like bacteria entering a wound. Its purpose is to prevent germs entering the blood circulation and to clear up damaged tissue
How Inflammation Occurs.
The process can be divided into four major stages.
- Blood vessel dilation: initially the small blood vessels in the area constrict and then quickly dilate. This dilation slows the blood flow through the injured area and causes the redness and heat that we experience.
- Migration of white blood cells: these cells wiggle through the wall of the dilated blood vessels and into the surrounding injured area. Their task is to mop up micro-organisms and clear up damaged tissue. They do this by phagocytosis (engulfing the bacteria). During this process many white blood cells die. Pus, which is often associated with inflammation, is simply large numbers of dead white cells.
- Movement of protein and water from blood vessels: this is what causes the swelling. The protein contains antibodies which neutralise micro-organisms.
- Initiation of clotting: with the water and proteins come substances that initiate clotting to prevent blood loss from the wound. One of these substances is fibrin – a stringy substance that forms a mesh. It is fibrin that is responsible for deaths that can occur in diphtheria: the fibrin mesh forms in the throat preventing air from reaching the lungs.
Control of Inflammation
As inflammation is a necessary but potentially dangerous process, the body has complex mechanisms for initiating and controlling it. In fact the healing and repair of the wound can't take place until the inflammatory reaction has been stopped.
Injury to the tissues initiates a cascade of chemical reactions which bring about the inflammatory process. One of the stages in the cascade involves the production of prostaglandins, a group of chemicals, some of which switch on inflammation and others help switch it off. A potent product of this cascade is a substance called histamine. This chemical irritates nerve endings to cause the pain and itching associated with inflammation.
Steroid drugs, aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) control pain and reduce inflammation by interfering with the reactions which produce pro-inflammatory prostaglandins. Very potent anti-inflammatories like steroid drugs have the drawback of potentially encouraging bacterial infection by suppressing inflammation. This does not appear to be the case with aspirin and other NSAIDs.
This article is for information only. If you have any concerns about your health, it's a good idea to consult your doctor.
Resources
An Introduction to General Pathology, Spector and Axford. pub. Churchill Livingston 1999
