Inflammation
Inflammation is the complex defence response triggered due to cell injury and found in vascularized connective tissue. It eliminates the injurious agents and remove the damaged tissue components so that healing can take place. Inflammation leads to accumulation of fluids and leukocytes in extracellular tissues. Inflammation is associated with repair and healing. In this article we will discuss about inflammation, clinical signs of inflammation, different types of inflammation and mechanism of inflammation.
Clinical signs of inflammation
Inflammation can be diagnosed by its cardinal signs given by Celsus,
- Rubor: Redness
- Tumour: Swelling
- Color: Heat
- Dolor: Pain
- Function lasea: Loss of function
Types of inflammation
Based on the time duration, inflammation is of two types,
- Acute inflammation
- Chronic inflammation
Acute inflammation
Acute inflammation is of short duration and can last for few hours to few weeks. The episode of acute inflammation may range from mild to very severe. Acute inflammatory response is described in a series of overlapping stages as follows,
- Increased blood flow
- Increased formation of tissue fluid
- Migration of leukocytes
Increased blood flow
The arterioles and local capillaries supplying blood to the damaged area get dilates. This dilation is caused by locally released chemical mediators from damaged cell, for example histamine and serotonin. Which leads to increased blood flow to the site of inflammation. This increased blood flow causes redness and increase in temperature. The increased blood flow provides more oxygen and nutrients for increased cellular activity.
Some of the most important substances released in inflammation are given in below table
Increased formation of tissue fluid
Formation of tissue fluid leads to swelling (oedema) of the tissue involved. There are two main causes oedema,
Increased permeability of small blood vessel walls: This is caused by inflammatory mediators, e.g. prostaglandins and histamines. Due to increased permeability of blood vessels, there is movement of excess fluid and plasm proteins. Excess fluid leaves the blood through permeable blood vessels and enters the tissue. Plasma proteins leave the blood by decreasing osmotic pressure of blood, hence water moves from blood stream into the tissues.
Increased hydrostatic pressure: The increased blood flow creates the hydrostatic pressure and forces fluid out of the vessels and into the tissues. Due to this most of the inflammatory exudate, phagocytes and cell debris are removed in lymph.
Migration of leukocytes
Loss of fluid from blood increases its thickness, decrease flow and allows white blood cells to adhere to vessel wall. In acute stages neutrophil adhere to blood vessel lining, squeezes between endothelial cells. After about 24 hours, macrophages become the predominant cell type at the site of inflammation. If inflammation is not cured in this period it leads to chronic inflammation.
Outcomes of acute inflammation
The outcomes for any acute inflammation can be one of the following four,
- Resolutions: The restoration of acute inflammation to the normal is called as resolution.
- Healing by fibrosis: Healing by connective tissue called as fibrosis. It is observed if tissue damage is extensive and unable to regenerate.
- Suppuration: It is a formation of pus, occurs in infections caused by pyrogenic organisms.
- Progression to chronic inflammation: Long continue tissue injury results in chronic inflammation.
Factors determining variation in acute inflammation
Organism related
| Factor | Role |
| Type of infection | Different infections have different target areas. E.g. pneumococci cause lobar pneumonia. |
| Extent of virulence | Determine production of exotoxin and extent of its effect. |
| Dose or concentration | Smaller concentration cause lesions while large concentration spread infection. |
| Products of organism | Production of various enzymes results in spread of infection. |
Host related
| Factor | Role |
| General health | Poor health increases severity of inflammation. |
| Immune status | Poor immunity increases the spread of infection. |
| Route of entry | Particular route is essential to cause infection. E.g. vibrio cholerae cause cholera only on oral entry. |
| Type of tissue | Rate of spread of inflammation depend on targeted tissue. Loose texture tissue is more susceptible for inflammation. |
Exudation related
| Factor | Role |
| Serous | Fluid exudates resemble serum cause easy spread of blisters. |
| Fibrous | High fibrin content facilitates fibrosis. |
| Purulent | Promote formation of pus and abscess. |
| Haemorrhagic | Involves vascular damage. |
Cell proliferation related
| Factor | Role |
| Slow | Bacterial infection shows slow proliferation. |
| Moderate | Observed in viral infection. |
| Rapidly progressive | Rapid change in clinical condition with rapid damage. |
Benefits of acute inflammation
Dilution of toxins: Exudate dilutes the bacterial toxins and other harmful chemicals.
Antibodies: Exudate consist antibodies which act against causative organism.
Fibrin formation: Exudates contain fibrinogen which helps in fibrin formation which facilitate the process of phagocytosis and restrict the bacterial spread.
Plasma mediator system: This ensures the continuous supply of mediators hence provide constant protection.
Nutrition: The exudates supply essential nutrients like oxygen, glucose, etc.
Removal of waste: Exudates remove waste products, produced during inflammation through lymphatic channel.
Harmful effects of acute inflammation
- Swelling of inflamed cells leading to serious mechanical effects.
- Inadequate blood supply and thereby impaired functioning.
Systemic manifestation of acute inflammation
Pyrexia: Increase in body temperature due to release of mediators like prostaglandins, interleukins, etc. These mediators affect thermostat function of hypothalamus.
Shock: Increased vasodilation with increase vascular permeability and loss of intravascular volume results in hypotension followed by shock.
Leucocytosis: Leucocytosis and leukemoid reaction seen with acute inflammation.
Lymphangitis: The lymph nodes involve in drain of inflamed tissue shows reactive inflammatory changes called lymphangitis.
Chronic inflammation
If the inflammation lasts for weeks or months it is known as the chronic inflammation. In chronic inflammation tissue destruction and attempts to healing observed together. Chronic inflammation may be a complication of acute inflammation or a primary condition of slow onset. Chronic infection may cause because of,
- Recurrent infections by certain microorganisms. E.g. tubercule bacilli
- Prolong exposure to toxic agents. E.g. inhalation of silica particles
- Autoimmune reaction. E.g. rheumatoid arthritis
The chronic inflammation has following three stages.
- Mononuclear infiltration: First stage is observed as infiltration by mononuclear cells like phagocytes, which includes circulating monocytes, tissue macrophages, epithelioid cells and lymphoid cells.
- Tissue destruction: The substances are released in inflammation process results in tissue destruction, in severe cases it can converted into necrosis.
- Proliferation: In this stage of tissue repair, connective tissue is replaced. Proliferation of small blood vessels is known as angiogenesis.
Types of chronic inflammation
Based on the site of inflammation, it can be divided into two types,
Specific chronic inflammation
When a causative agent causes a specific tissue response it is known as the specific chronic inflammation.
Non-specific chronic inflammation
When causative agent causes a non-specific response with formation of granulation tissue it is known as the non-specific chronic inflammation.
Conclusion
An inflammation can be identified by its cardinal signs such as, redness, swelling, heat, pain and loss of function. Inflammation is one of the body’s primary defence mechanisms. Mechanism of inflammation involves immune cells, cytokines and chemical mediators. Deeper understanding of inflammation contributes to the development of targeted approach for managing inflammatory disorders.
Frequently asked questions
What is exudate?
Exudate is body fluid that come out from the blood vessels into the nearby tissue during inflammation. The fluid exudes out via the pores or a wound.
What is leucocytosis?
Leucocytosis is a condition characterised by increased levels of leucocytes (WBCs). It can occur due to the infection or inflammation to the body.
What is chemotaxis?
Chemotaxis is the movement of an organism or entity in response to a chemical stimulus.
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