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also plethora, an excess of blood in a tissue or organ. One may distinguish arterial and venous hyperemia. Arterial (active) hyperemia arises as a result of increased blood flow in the arteries owing to increased tonus of the vasodilator nerves or decreased tonus of the vasoconstrictor nerves. Among its causes are increased sensitivity of the blood vessels to physiological stimuli or the influence of extraordinary stimuli (such as bacterial toxins, high temperature, and products of tissue decomposition); in humans psychogenic factors (such as shame and anger) play a large role. Arterial hyperemia is characterized by dilatation of the arteries in the hyperemized area, elevation of temperature in the area, acceleration of blood flow, and reddening (for example, hyperemia of the face). It is accompanied by intensification of metabolic processes in the tissues and promotes the regeneration of tissues. Hemorrhages may occur during arterial hyperemia if there are pathological changes in the blood vessels. Arterial hyperemia is induced for therapeutic purposes by means of mustard plasters and cupping glasses. Venous (passive, static) hyperemia occurs when the outflow of blood along the veins is obstructed as a result of pressure on the venous wall (cicatrix, tumor, varicose dilatation of the veins, or edema), while the inflow remains unchanged or when there is a weakening of cardiac activity. Venous hyperemia is characterized by deceleration of blood flow to the point of complete stasis. Oxygen deficit develops in the tissues, the vascular walls become more permeable, and edema develops. Prolonged blood stasis and edema may lead to atrophy of the parenchyma of an organ.
V. A. FROLOV