Inflammation

The innate immune system is programmed to respond to damage to the body, whether the damaged tissue is septic or sterile. That response rapidly initiates an interactive system of humoral (soluble in the blood) and cellular systems, called inflammation. Inflammation is the first response to injury.

The inflammatory response:

• occurs in tissues with a blood supply (vascularized)
• is activated rapidly (within seconds) after damage occurs
• depends on the activity of both cellular and chemical components
• is nonspecific

The classic symptoms of acute inflammation include redness (erythema), heat, swelling, pain, and loss of function. Microscopic inflammatory changes occur within seconds in the microcirculation (arterioles, capillaries, and venules) near the site of an injury and include the following processes:

• Vasodilation (increased size of the blood vessels), which causes slower blood velocity and increases blood flow to the injured site
  
• Increased vascular permeability (the blood vessels become porous from contraction of endothelial cells) and leakage of fluid out of the vessel (exudation), causing swelling (edema) at the site of injury; as plasma moves outward, blood in the microcirculation becomes more viscous and flows more slowly, and the increased blood flow and increasing concentration of red cells at the site of inflammation cause locally increased redness (erythema) and warmth.
• White blood cell adherence to the inner walls of vessels and their migration through enlarged junctions between the endothelial cells lining the vessels into the surrounding tissue.

There are several benefits of inflammation, including the following:

• Prevents infection and further damage by contaminating microorganisms through the influx of plasma to dilute toxins produced by bacteria and released from dying cells, the influx and activation of plasma protein systems that help contain and destroy bacteria  (e.g., complement system, clotting system), and the influx of cells (e.g., neutrophils, macrophages) that destroy cellular debris and infectious agents.
• Limits and control the inflammatory process through the influx of plasma protein systems (e.g., clotting system), plasma enzymes, and cells (e.g., eosinophils) that prevent the inflammatory response from spreading to areas of healthy tissue.
• Interacts with components of the adaptive immune system to elicit a more specific response to contaminating pathogen(s) through the influx of macrophages and lymphocytes.
• Prepares the area of injury for healing through removal of bacterial products, dead cells, and other products of inflammation (e.g., by way of channels through the epithelium or drainage by lymphatic vessels) and initiation of mechanisms of healing and repair.

All Images Related

Acute Inflammatory Response

Plasma Protein Systems in Inflammation: Complement, Clotting and
Kinin system

Principal Mediators of Inflammatory Processes

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