inflammation
Meaning of inflammation: Useful in the short term and damaging when it persists, inflammation is protective or destructive depending largely on how long it lasts.
Definition of inflammation
Inflammation is the body's coordinated response to anything that damages tissue, whether injury, infection, an irritant or an immune reaction. Blood vessels widen and leak, and white blood cells move into the area to clear the cause and begin repair. The classic signs are redness, warmth, swelling, pain and loss of function, though not all appear in every case.
What happens in the tissue?
Damage is detected by cells already stationed in the tissue, and they release chemical signals. Small blood vessels nearby widen, so more blood arrives, producing redness and warmth. The vessel walls turn leaky, letting fluid and proteins escape into the tissue, which produces swelling. Some of the released chemicals sensitize nerve endings, producing pain, and swelling and pain together limit use of the part, the fifth classic sign. White blood cells then stick to the vessel walls and squeeze between the cells lining them to reach the site, where they engulf debris and any organisms present. A raised white blood cell count in a blood sample often reflects that recruitment.
Is inflammation the same as infection?
| Inflammation | Infection | |
|---|---|---|
| What it is | The body's response | An organism multiplying within tissue |
| Requires a microbe | No | Yes |
| Example of one without the other | Sprained ankle, gout, autoimmune arthritis | Infection in someone whose immune response is suppressed |
| Relationship between them | Infection is one trigger among many | Infection almost always provokes it |
The two words are used interchangeably in everyday speech and should not be. Cellulitis, a bacterial infection of the skin, is inflamed because it is infected. A sprained ankle is inflamed with no organism involved at all. What is done about each differs completely, so the distinction is not a technicality.
How do acute and chronic inflammation differ?
Acute inflammation develops within minutes to hours, is driven largely by neutrophils, and resolves once the trigger has been dealt with, leaving repaired tissue behind. Chronic inflammation persists for months or years. It is driven by a different set of cells, including macrophages and lymphocytes, and it involves destruction and attempted repair proceeding at the same time, so scarring accumulates alongside continuing damage. It arises when the trigger cannot be cleared, when an immune response is directed at the body's own tissue, or when exposure to an irritant continues. Long-running low-grade inflammation is associated with atherosclerosis, with some cancers and with metabolic disease, which is why it is studied well beyond the settings where redness and swelling can be seen.
Also known as
Used in a sentence
Laboratory and imaging findings suggested inflammation around the joint.
Good to know
Inflammation can be acute or chronic, and it is not synonymous with infection, since injury, autoimmune disease and irritants all produce it without any organism being present.
Word origin
Where “inflammation” comes from
From Latin inflammare, meaning to set on fire, formed from in-, meaning into, and flamma, meaning flame.