The word inflammation is derived from the Latin term "inflammo", meaning "I set alight, I ignite".
Inflammation is part of body's wisdom. Inflammatory process is a complex interactive cascade/web of transformation of local and systemic environment involving inflammatory cells and pro-inflammatory chemicals in the blood, blood vessels and site of tissue injury and beyond.
Inflammation is not analogous to infection although inflammation is result of an infection by pathogens as simple as flu.
Purpose of inflammation
It is the body’s natural immune response to combat any offending irritant or pathogen that attacks our body with potential for harm. Inflammation may be thought of as a defense mechanism that we are born with and performs the follows actions,
- Isolates damaged area
- Protects against harmful agents/stimuli
- Demolishes or eliminates the harmful agent/pathogen as well as the, damaged cells attacked by the harmful agent.
- Begins the repair after the offending agent has been addressed to allow for healing and bring the tissue/organ back to its healthy baseline as much as possible.
- Goal is to limit inflammation in a controlled fashion. Key is not just to treat but prevent. The best benefits are achieved by the body when it individualizes the response and adjusts accordingly.
When does the inflammation occur?
When body senses danger, it marshalls’ it’s immune system forces to combat the offender, and then to help repair the aftermath. The harmful agent or danger may be physical, chemical or biologic pathogen. Inflammation may be good or bad depending upon the context.
Where does inflammatory process occur?
The inflammatory reaction or process occurs not just at the site of injury but also in distant parts of body. For example, think about systemic fever as a result of infection in one discreet part of body.
What causes acute inflammation?
- When something harmful or irritating affects any part of our body, acute inflammation occurs. It is frequently a self-limiting or relatively easily treatable phenomenon that resolves upon effective treatment of the cause like infection or trauma. Chronic inflammation quite simply represents the other end of the spectrum.
- Acute inflammation either gets resolved as healing process wins the day, transforms into an abscess, or evolves into chronic inflammation.
What causes chronic inflammation?
Chronic inflammation frequently represents an uncontrolled, poorly regulated, over-active and self-sustaining inflammatory torrent of events:
- Infections providing continued stimulus for inflammation, e.g. tuberculosis
- Environmental offenders/toxins like pollens, smoking, traffic pollution
- Persistent foreign body in the body
- Autoimmune reaction
- Persistence of inflammatory mediators resulting in persistent inflammation.
Acute versus chronic inflammation
Acute inflammation starts quickly, rapidly progressing to its peak. Manifestations of acute inflammation may last a few days to sometimes a few weeks. It requires the constant presence of the offending agent and resolves once the offendor has been taken care of. Examples include acute respiratory infection, injury to hand/knee/foot etc.
Chronic inflammation occurs over long term lasting from months to years due to inability of the body to effectively combat the infection. Other times, it may occur due to self-sustaining inflammation seen in autoimmune diseases wherein body’s immune system actually attacks body’s own tissues mistaking it for alien and harmful. Still another scenario would be wherein a low grade inflammation persists, for example due to bad orodental hygiene, stomach ulcers etc.
Components of inflammatory process
Leukocytes or white blood cells are critically involved in the initiation and sustaining the inflammatory processes. These WBCs arrive at the site of injury or infection from their usual location in the blood, migrate across the blood vessel wall into the surrounding tissues.
Acute inflammation involves inflammatory cells like neutrophils, basophils, eosinophils, and mononuclear cells like macrophages, monocytes in addition to a variety of inflammatory mediators. Complement system may be activated.
Chronic inflammation involves mononuclear cells like macrophages, lymphocytes, plasma cells as well as fibroblasts . The inflammatory cascade is mediated via reactive oxygen species, interferon,cytokines along with growth factors etc. The result is tissue death, healing and scarring; all these processes may be occurring simultaneously.
Plasma cascade systems involved in inflammation include complement system, kinin system, coagulation system and fibrinolysis system.
Signs/symptoms of inflammation
The names are derived from 5 Latin terms:
- Rubor or redness: Redness occurs as a result of increased blood flow to the site of inflammation
- Calor or heat/ warmth
- Tumor which stands for edema/swelling: Swelling occurs as more fluid and proteins including antibodies exude out of the blood vessels into the surrounding tissues
- Dolor or pain
- Functio laesa or decreased function or immobility
The first four features were documented in De Medicina by a Roman medical writer named Aulus Cornelius Celsus. It is unclear who came up with the fifth feature, i.e.loss of function.
What is the significance of various signs of inflammation?
The signs and symptoms of inflammation, specifically acute inflammation, show that the body is trying to combat the danger and heal the damaged tissues. All the signs may or may not be present in all circumstances.
Many of the signs of inflammation may not be visible if the site of inflammation is deep inside the body, e.g. pneumonia in case of lung infection.
Process of Acute Inflammation with specific reference to gut
First defenses are mounted by cells already present in the tissues themselves. The gut which has the highest amount of pathogenic load due to trillions of bacteria along with toxins present in the gut lumen represents the largest immune organ of all. The inflammatory cells of gut include resident macrophages, dendritic cells, histiocytes, and mast cells.
Initially there is dilation of blood vessels supplying the site of injury resulting in increased blood Supply. The blood capillaries become leaky which facilitates seepage of fluid out of the blood vessels into the surrounding tissue.
Along with the fluid seepage also come the cells involved in inflammation starting with neutrophils that are the body;s first line of defense. A wide variety of leukocytes like granulocytes, monocytes and lymphocytes are involved.
Neutrophils form the tip of the spear and are the firsts ones to arrive at the site of inflammation.
The surface of these cells have Pattern Recognition Receptors (PRRs), which recognize pathogenic organisms and can differentiate between an invading organism and the body’s own cells. Activation of PRRs by infection, trauma, irritant, toxin initiates the process of inflammation releasing in inflammatory mediators.
They engulf the pathogenic organism and kill it via nonspecific armaments like oxygen free radicals.
Neutrophils also release many antimicrobial proteins as well as proinflammatory cytokines like tumor necrosis factor and interferon which in turn stimulate increased synthesis and release of acute phase reactant proteins along with spreading the process of inflammation throughout the body.
Process of chronic inflammation
The main white cells involved in chronic inflammation are monocytes which engulf and kill the pathogens as well as the older damaged cells. Like other white cells, they are also source of pro-inflammatory chemicals. Over time lymphocytes also arrive at the scene.
Antibodies of various types against the purported pathogen are formed and released. Sometimes, these antibodies have a “mis-recognition” and may target and hurt body’s own tissues. Another process involves the antibody-antigen complex stimulating the complement system further kindling the release of a variety of intermediaries of inflammation.
The reactive oxygen species and pro-inflammatory mediators in addition to killing the harmful pathogens also damage the body’s own tissues. Chronic inflammation involves healing of damaged tissues as well as formation of new blood vessels at the site along with regeneration of cells and scar tissue.
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