Inflammation is the immediate response of the body to injury. It involves activation of blood proteins (that is - coagulation factors and complement proteins) and the stimulation of inflammatory cells. During inflammation, capillary endothelial cells at sites of tissue injury become leaky, allowing the movement of fluid from the intra-vascular space into the interstitial space. This fluid is called edema fluid. Leukocytes enter injured tissues to kill microbes and remove necrotic debris.

It is worth emphasizing that inflammation is a normal and healthy response of the body to all types of cell injury. It is closely associated in time and space with mechanisms or tissue repair, regeneration and fibrosis (that is - wound healing).

Here are the Key Points:

1. Acute inflammation is an immediate response of the microcirculation to injury resulting in hyperemia, edema, and movement of leukocytes into sites of injury.

2. Mediators of inflammation include plasma proteins (that is - soluble mediators).

3. Mediators of inflammation also include blood cells (that is - cellular mediators).

4. Possible outcomes include: i) acute inflammation with resolution, ii) chronic inflammation, and iii) granulomatous inflammation.

5. Systemic manifestations of inflammation include fever, leukocytosis, decreased appetite and altered sleep patterns.

The following images illustrate Key Morphological Concepts:

1. This is an example of ACUTE INFLAMMATION affecting the skin of the forearm. The cardinal signs of inflammation are clearly evident. They include swelling (tumor), redness (rubor) and warmth (calor). This deep-seated bacterial infection of the skin is also referred to as a carbuncle.

2. This is an example of LEUKOCYTE MARGINATION and sludging of erythrocytes at a site of tissue injury. Leukocytes leave the intra-vascular space and undergo directed cell migration towards sites of necrosis or infection. Directed cell migration is also termed chemotaxis.

3. This is an example of ACUTE PNEUMONIA. The small air spaces in the lung (alveoli) are completely filled with polymorphonuclear leukocytes. These cells are also referred to as neutrophils, based on their lack of staining with special dyes.

4. This is an example of an EOSINOPHIL RESPONSE during chronic inflammation. The large cells with pink cytoplasm are eosinophils. They are seen surrounding a blood vessel. Eosinophils are commonly activated in allergic reactions and parasitic infestations.

5. This is an example of a FIBRIN-RICH EXUDATE forming on the surface of the heart. Note the "bread and butter" appearance. This exudate represents the activation of acute inflammation on the surface of the heart. It is also referred to as fibrinous pericarditis. Fibrin is end-product of the coagulation cascade and the major protein in blood clots.