inflammation - Characteristics, Leukocytes and cytokines, Outcomes, Systemic inflammation, Inflammation examples, Other References

The body's reaction to injury, whether caused by a physical or chemical insult, an infectious agent, or an auto-immune process. In the acute stage there is an increased blood flow to the damaged part, due to chemical substances which dilate the small blood vessels. Certain types of white blood cells (neutrophil polymorphs and monocytes) are attracted to the site, and these engulf and digest damaged tissue and any infectious micro-organisms (phagocytosis). The reaction is accompanied by pain, heat, swelling, redness, and loss of function of the affected part. If the defence is successful, the tissues reorganize and repair themselves; if not, the inflammation may become chronic or an abscess may develop.

Inflammation is characterised by the following quintet: redness (rubor), heat (calor), swelling (tumor), pain (dolor) and dysfunction of the organs involved (functio laesa).

Characteristics

Inflammation has two main components - cellular and exudative.

The cellular component involves the movement of white blood cells from blood vessels into the inflamed tissue. The white blood cells, or leukocytes, take on an important role in inflammation; Blood vessels are dilated upstream of an infection (causing redness and heat) and constricted downstream while capillary permeability to the affected tissue is increased, resulting in a net loss of blood plasma into the tissue - giving rise to edema or swelling.

If inflammation of the affected site persists, released cytokines IL-1 and TNF will activate endothelial cells to upregulate receptors VCAM-1, ICAM-1, E-selectin, and L-selectin for various immune cells.

Neutrophils are characteristic of inflammation in the early stages - they are the first cells to appear in an infected area, and any section of recently inflamed (within a couple of days or so) tissue viewed under a microscope will appear packed with them. Neutrophils only live for a couple days in these interstitial areas, so if the inflammation persists for a longer duration then they are gradually replaced by longer lived monocytes.

Leukocytes and cytokines

Various leukocytes are involved in the initiation and maintenance of inflammation. Generally speaking, acute inflammation is mediated by granulocytes or polymorphonuclear leucocytes, while chronic inflammation is mediated by mononuclear cells such as monocytes and cat macrophages. These cells can be further stimulated to maintain inflammation through the action of an adaptive cascade involving lymphocytes: T cells, B cells, and antibodies.

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Outcomes

The outcome in a particular circumstance will be determined by the tissue in which the injury has occurred, and the injurious agent that is causing it.

There are four possible results to inflammation:

Resolution, the complete reconstitution of damaged tissue, does not usually occur in the body. Some 24 hours after inflammation in a wound first occurs, the wound healing response will commence. This response involves the formation of connective tissue to bridge the gap caused by injury, and the process of angiogenesis, the formation of new blood vessels, to provide nutrients to the newly formed tissue. If the injurious agent continues, chronic inflammation will ensue. This process, marked by inflammation lasting many days, months or even years, may lead to the formation of a chronic wound. Chronic inflammation is characterised by a dominating presence of macrophages in the injured tissue, which extravasate via the same methods discussed above (ICAM-1 VCAM-1). This is why chronic inflammation is almost always accompanied by tissue destruction.

Systemic inflammation

Sepsis

When inflammation overwhelms the whole organism, systemic inflammatory response syndrome (SIRS) is diagnosed. Although the processes involved are identical, this form of inflammation is not confined to a particular tissue but involves the endothelium (lining of blood vessels) and many other organ systems.

Inflammation examples

Inflammation is usually indicated by adding the suffix "-itis", as shown below.

appendicitis: appendix gastritis: stomach laryngitis: larynx meningitis: meninges (the membrane covering the brain) otitis: ear pancreatitis: pancreas

More examples are available at list of types of inflammation.

Other References

Anti-inflammatories can reduce the pain associated with inflammation.