Fig. 3.15 ). Ulceration can occur only when tissue necrosis and resultant inflammation exist on or near a surface. It is most commonly encountered in (1) the mucosa of the mouth, stomach, intestines, or genitourinary tract, and (2) the skin and subcutaneous tissue of the lower extremities in older persons who have circulatory disturbances that predispose to extensive ischemic necrosis. Acute and chronic inflammation often coexist in ulcers, such as peptic ulcers of the stomach or duodenum and diabetic ulcers of the legs. During the acute stage there is intense polymorphonuclear infiltration and vascular dilation in the margins of the defect. With chronicity, the margins and base of the ulcer develop fibroblast proliferation, scarring, and the accumulation of lymphocytes, macrophages, and plasma cells.
Although, as might be expected, many variables may modify the basic process of inflammation, including the
Fig. 3.14 Purulent inflammation. (A) Multiple bacterial abscesses (arrows) in the lung in a case of bronchopneumonia. (B) The abscess contains neutrophils and cellular debris, and is surrounded by congested blood vessels.
http://ebooksmedicine.net
Fig. 3.15 The morphology of an ulcer. (A) A chronic duodenal ulcer. (B) Low-power cross-section view of a duodenal ulcer crater with an acute inflamma tory exudate in the base.
nature and intensity of the injury, the site and tissue affected, and the responsiveness of the host, acute inflammatory reactions typically have one of three outcomes
Fig. 3.16): • Complete resolution. In a perfect world, all inflammatory reactions, after they have succeeded in eliminating the offending agent, should end with restoration of the site of acute inflammation to normal. This is called resolution and is the usual outcome when the injury is limited or short-lived or when there has been little tissue destruction and the damaged parenchymal cells can regenerate. Resolution involves removal of cellular debris and microbes by macrophages, and resorption of edema fluid by lymphatics.
• Healing by connective tissue replacement (scarring, or fibrosis). This occurs after substantial tissue destruction, when the inflammatory injury involves tissues that are incapable of regeneration, or when there is abundant fibrin exudation in tissue or in serous cavities (pleura, peritoneum) that cannot be adequately cleared. In all
Clearance of injurious stimuli
Clearance of mediators and acute inflammatory cells • Replacement of injured cells • Normal function FIBROSIS • Loss of function CHRONIC INFLAMMATION • Angiogenesis • Mononuclear cell infiltrate • Fibrosis (scar) Progression Healing Pus formation (abscess) Healing Healing
Fig. 3.16 Outcomes of acute inflammation: resolution, healing by fibrosis, or chronic inflammation.The components of the various reactions and their functional outcomes are listed.
http://ebooksmedicine.net these situations, connective tissue grows into the area of damage or exudate, converting it into a mass of fibrous tissue.
• Progression of the response to chronic inflammation. Acute to chronic transition occurs when the acute inflammatory response cannot be resolved, as a result of either the persistence of the injurious agent or some interference with the normal process of healing.
Chronic inflammation is a response of prolonged duration (weeks or months) in which inflammation, tissue injury, and attempts at repair coexist, in varying combinations. It may follow acute inflammation, as described earlier, or may begin insidiously, as a smoldering, sometimes progressive, process without any signs of a preceding acute reaction.
Causes of Chronic Inflammation
Chronic inflammation arises in the following settings: