Inflammatory response

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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