Everything about Inflammation totally explained
Inflammation (
Latin,
inflammatio, to set on fire) is the complex biological response of
vascular tissues to harmful stimuli, such as
pathogens, damaged cells, or irritants. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation isn't a synonym for
infection. Even in cases where inflammation is caused by infection it's incorrect to use the terms as synonyms: infection is caused by an exogenous pathogen, while inflammation is the response of the organism to the pathogen.
In the absence of inflammation, wounds and infections would never heal and progressive destruction of the tissue would compromise the survival of the organism. However, inflammation which runs unchecked can also lead to a host of diseases, such as
hay fever,
atherosclerosis, and
rheumatoid arthritis. It is for this reason that inflammation is normally tightly regulated by the body.
Inflammation can be classified as either
acute or
chronic.
Acute inflammation is the initial response of the body to harmful stimuli and is achieved by the increased movement of
plasma and
leukocytes from the blood into the injured tissues. A cascade of biochemical events propagates and matures the inflammatory response, involving the local
vascular system, the
immune system, and various cells within the injured tissue. Prolonged inflammation, known as
chronic inflammation, leads to a progressive shift in the type of cells which are present at the site of inflammation and is characterised by simultaneous destruction and healing of the tissue from the inflammatory process.
Causes
Types
>
| |
Acute |
Chronic |
| Causative agent |
Pathogens, injured tissues |
Persistent acute inflammation due to non-degradable pathogens, persistent foreign bodies, or autoimmune reactions |
| Major cells involved |
Neutrophils, mononuclear cells (monocytes, macrophages) |
Mononuclear cells (monocytes, macrophages, lymphocytes, plasma cells), fibroblasts |
| Primary mediators |
Vasoactive amines, eicosanoids |
IFN-γ and other cytokines, growth factors, reactive oxygen species, hydrolytic enzymes |
| Onset |
Immediate |
Delayed |
| Duration |
Few days |
Up to many months, or years |
| Outcomes |
Healing, abscess formation, chronic inflammation |
Tissue destruction, fibrosis |
Acute inflammation
>
| English |
Latin |
| Redness |
Rubor* |
| Heat |
Calor* |
| Swelling |
Tumor* |
| Pain |
Dolor* |
| Loss of function |
Functio laesa** |
| All the above signs may be observed in specific instances, but no single sign must, as a matter of course, be present.These are the original, so called, "cardinal signs" of inflammation.**
|
Acute inflammation is a short-term process which is characterized by the classic signs of inflammation - swelling, redness, pain, heat, and loss of function - due to the infiltration of the tissues by plasma and
leukocytes. It occurs as long as the injurious stimulus is present and ceases once the stimulus has been removed, broken down, or walled off by scarring (
fibrosis). The first four characteristics have been known since ancient times and are attributed to
Celsus.
Loss of function was added to the definition of inflammation by
Virchow in the 19th century (1870).
The process of acute inflammation is initiated by the blood vessels local to the injured tissue, which alter to allow the exudation of
plasma proteins and
leukocytes into the surrounding tissue. The increased flow of fluid into the tissue causes the characteristic swelling associated with inflammation since the
lymphatic system doesn't have the capacity to compensate for it, and the increased blood flow to the area causes the reddened colour and increased heat. The blood vessels also alter to permit the extravasation of leukocytes through the
endothelium and
basement membrane constituting the blood vessel. Once in the tissue, the cells migrate along a
chemotactic gradient to reach the site of injury, where they can attempt to remove the stimulus and repair the tissue.
Meanwhile, several biochemical cascade systems, consisting of chemicals known as plasma-derived inflammatory mediators, act in parallel to propagate and mature the inflammatory response. These include the
complement system,
coagulation system and
fibrinolysis system.
Finally, down-regulation of the inflammatory response concludes acute inflammation. Removal of the injurious stimuli halts the response of the inflammatory mechanisms, which require constant stimulation to propagate the process. Additionally, many inflammatory mediators have short half lives and are quickly degraded in the tissue, helping to quickly cease the inflammatory response once the stimulus has been removed. and
anti-inflammatory drugs work specifically by inhibiting normal inflammatory components.
Cancer
Inflammation orchestrates the microenvironment around tumours, contributing to proliferation, survival and migration. Cancer cells use
selectins,
chemokines and their receptors for invasion, migration and metastasis. On the other hand, many cells of the immune system contribute to
cancer immunology, suppressing cancer.
Termination
The inflammatory response must be actively terminated when no longer needed to prevent unnecessary "bystander" damage to tissues.|30px|30px|Charles Serhan}}
Systemic effects
An organism can escape the confines of the immediate tissue via the
circulatory system or
lymphatic system, where it may spread to other parts of the body. If an organism isn't contained by the actions of acute inflammation it may gain access to the lymphatic system via nearby
lymph vessels. An infection of the lymph vessels is known as
lymphangitis, and infection of a lymph node is known as
lymphadenitis. A pathogen can gain access to the bloodstream through lymphatic drainage into the circulatory system.
When inflammation overwhelms the host,
systemic inflammatory response syndrome is diagnosed. When it's due to
infection, the term
sepsis is applied, with
bacteremia being applied specifically for bacterial sepsis and
viremia specifically to viral sepsis.
Vasodilation and organ dysfunction are serious problems associated with widespread infection that may lead to
septic shock and death.
Acute-phase proteins
Inflammation also induces high systemic levels of
acute-phase proteins. In acute inflammation, these proteins prove beneficial, however in chronic inflammation they can contribute to
amyloidosis During clinical studies, inflammatory-related molecule levels were reduced and increased levels of anti-inflammatory molecules were seen within four weeks after patients began a very low calorie diet. The association of systemic inflammation with
insulin resistance and
atherosclerosis is the subject of intense
research.
Outcomes
The outcome in a particular circumstance will be determined by the tissue in which the injury has occurred and the injurious agent that's causing it. There are three possible outcomes to inflammation:
The complete restoration of the inflamed tissue back to a normal status. Inflammatory measures such as vasodilation, chemical production, and leukocyte infiltration cease, and damaged parenchymal cells regenerate. In situations where limited or short lived inflammation has occurred this is usually the outcome.
Fibrosis
Large amounts of tissue destruction, or damage in tissues unable to regenerate, can not be regenerated completely by the body. Fibrous scarring occurs in these areas of damage, forming a scar composed primarily of collagen. The scar won't contain any specialized structures, such as parenchymal cells, hence functional impairment may occur.
Abscess Formation
A cavity is formed containing pus, an opaque liquid containing dead white blood cells and bacteria with general debris from destroyed cells.
Chronic inflammation
In acute inflammation, if the injurious agent persists then 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 the dominating presence of macrophages in the injured tissue. These cells are powerful defensive agents of the body, but the toxins they release (including reactive oxygen species) are injurious to the organism's own tissues as well as invading agents. Consequently, chronic inflammation is almost always accompanied by tissue destruction.
Examples
Inflammation is usually indicated by adding the suffix "-itis", as shown below. However, some conditions such as asthma and pneumonia don't follow this convention. More examples are available at list of types of inflammation.
Image:Acute_Appendicitis.jpg|Acute appendicitis
Image:Dermatitis.jpg|Acute dermatitis
Image:Streptococcus pneumoniae meningitis, gross pathology 33 lores.jpg|Acute infective meningitis
Image:Tonsillitis.jpg|Acute tonsillitis
Further Information
Get more info on 'Inflammation'.
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