Histopathology

Abstract

The exchange process necessary for life takes place in the capillaries at a pressure of 13–32 mmHg. Pressure on the tissue which partially or completely occludes the capillaries impedes the inflow and outflow of blood. When this occurs for an extended period of time, tissue ischemia and hypoxia result. The lack of oxygen causes a shift from aerobic to anaerobic metabolism. As the lactate concentration increases, the pH decreases [1]. The amounts of histamine, bradykinin, prostaglandins, carbon dioxide, lysosomal enzymes, collagenase, hyaluronic acid, and hypoxanthine increase. Following the relief of pressure, during the reflow phase, there are increases in superoxide anion hydrogen peroxide and hydroxyl radicals [2], factor VIII, and uric acid. Fibrinolytic activity decreases. These changes lead to increased capillary permeability, edema, and finally cell death. Necrosis appears first in the secretory cells and ducts of the eccrine sweat glands and in the subcutaneous fat, and progresses to involve the sebaceous glands. The epidermis and the hair follicles are the last structures to be affected by ischemia and hypoxia.