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Clinically, acute inflammation is characterized by 5 cardinal signs: rubor (redness), calor (increased heat), tumor (swelling), dolor (pain), and functio laesa (loss of function) (Figure 3-1). The first four were described by Celsus (ca 30 bc–38 ad); the fifth was a later addition by Virchow in the nineteenth century. Redness and heat are due to increased blood flow to the inflamed area; swelling is due to accumulation of fluid; pain is due to release of chemicals that stimulate nerve endings; and loss of function is due to a combination of factors. These signs are manifested when acute inflammation occurs on the surface of the body, but not all of them will be apparent in acute inflammation of internal organs. Pain occurs only when there are appropriate sensory nerve endings in the inflamed site—for example, acute inflammation of the lung (pneumonia) does not cause pain unless the inflammation involves the parietal pleura, where there are pain-sensitive nerve endings. The increased heat of inflamed skin is due to the entry of a large amount of blood at body core temperature into the normally cooler skin. When inflammation occurs internally—where tissue is normally at body core temperature—no increase in heat is apparent.

Figure 3–1.

Cardinal signs of acute inflammation. Note swelling and redness of the skin around an infected burn. Marked tenderness, increased local temperature, and loss of function were also present.

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