Inflammatory response

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Describe the pathological changes that occur in the tissues during an inflammatory response.

Acute inflammation is a normal process that protects and heals the body. It lasts hours to days so is short lived. It is characterised by the presence of neutrophils. Chronic inflammation is an abnormal process that does not benefit the body. It is characterised by lymphocytes and macrophages. Active inflammation, tissue destruction and repair attempts all occur at the same time. It occurs in presistent infections, prolonged exposure to toxic agents and autoimmunity. It can last for years.

The damaged tissues release

chemical mediators, histamine and prostaglandins, which cause vasodilation of

the surrounding blood vessels and increased blood flow to the area. This process causes two of the cardinal signs

of inflammation - heat and redness.

These mediators also help increase permeability of the blood vessels,

allowing phagocytes and fluid to leak out into tissues causing swelling

(oedema) which is another cardinal sign.

The tissue is infiltrated by lots of white blood cells.

The red blood cells adhere

together in the vessel and the neutrophils move towards the vessel wall. This is a process known as

Margination/Pavementing. The neutrophils

then move out of the vessel into the interstitial fluid. Once the neutrophils are out, the macrophages

follow. This process is known as

Emigration/Diapedisis.

Chemotaxis attract neutrophils

and other white blood cells to the site of injury. Once the neutrophils and macrophages have

arrived at the site, they ingest the debris and bacterium. This process is known as Phagocytosis and can

lead to pus formation. The process is

helped by opsonins (proteins). They have

binding sites so that they can bind and mark bacteria ready for phagocytosis. A substance called complement also aids Phagocytosis

by breaking up and marking foreign cells for destruction.

Growth factors and fibroblasts

are then released to fuel the re-growth of tissue.

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