Inflammation is the body’s response to injury. When tissues are damaged and cells die, the body responds by mounting an inflammatory response. The purpose is protection of the cells and tissue from the damaging insults, and eventually leading to repair of damaged tissue and regrowth of cells. Paradoxically, the inflammatory process which is meant to be protective and reparative, can produce severe illness and may even cause death.
Tissue death leads to release of chemical substances that act on blood vessels and white blood cells to recruit them to the site of inflammation. Examples of such chemical mediators are histamine, prostaglandins, cytokines such as interleukins and tumor necrosis factor and proteins of the complement system. These chemicals result in redness, warmth and pain at the site of inflammation. The cytokines and prostaglandin are also responsible for causing fever that often accompanies inflammation. Nitric oxide is also produced and results in vasodilation. Anti-inflammatory medications such as NSAIDs and aspirin act by inhibiting the chemical inflammatory mediators in order to stop the whole process of inflammation.
During the early stages of inflammation, small blood vessels close to the area of tissue damage become dilated with increased blood flow. The blood flow slows down and the fluid leaks out of the vessels into the area of tissue damage. This results in swelling (edema) of the damaged tissue and the tissue surrounding it.
Inflammatory cell migration
White blood cells known as neutrophils and macrophages are responsible for killing the microorganisms that damage our cells and tissues, as well as for mopping up the debris left behind by dead cells. These cells migrate to the site of damaged tissue and form part of the acute inflammatory exudate. Neutrophils interact with the endothelial cells that form the wall of blood vessels and roll along the blood vessel wall in order to migrate to the site of damage. Neutrophils and macrophages engulf the microorganisms and dead cells by a process known as phagocytosis. Neutrophils also produce toxic free radicals to kill the microorganisms. Many neutrophils and dead cells in an inflammatory exudate are also known as pus.
Acute inflammatory exudate
The acute inflammatory exudate contains fluid, neutrophils and macrophages, as well as fibrin. The clotting pathway that is responsible for the clotting of blood is activated in inflammation and fibrin is produced from fibrinogen. Fibrin is a long filamentous protein that holds the neutrophils and macrophages together with the damaged cells in the area of inflammation. Fibrin is also responsible for the repair of the damaged tissue, forming scar tissue.
Acute inflammation can lead to either resolution, healing by repair or chronic inflammation. Resolution is when all damaged tissue is removed and there is regrowth of dead cells, leading to completely normal tissue. Healing by repair results in granulation tissue or scar formation. Eventually the scar tissue is dissolved and new cells regrow but this process can take a long time. Chronic inflammation occurs when there is continued tissue damage. In this case the inflammatory process continues with tissue damage and repair occurring at the same time.