Microvascular Aspects of Tissue Injury

This chapter focuses first on the vasomotor aspects of tissue injury, as these must be recognized and separated from other intrinsic derangements involving the blood–tissue barrier and the blood cellular elements.

Abstract

This chapter discusses the microvascular aspects of tissue injury. The somatic representations of the injury reaction of necessity represent the backbone or framework into which all other information must be incorporated on whatever level—ultrastructural, biochemical, or biophysical. The chapter focuses first on the vasomotor aspects, as these must be recognized and separated from other intrinsic derangements involving the blood–tissue barrier and the blood cellular elements. The terminal vascular bed represents the only access that the general population of cells has to the circulation. The capillary blood flow is believed to be monitored locally under physiologic conditions by tissue byproducts that counteract the vasomotor tone imposed on a systemic basis via the bloodstream and the nervous system. The major features of the inflammatory process—vasodilation, transudation of plasma proteins, and cellular emigration—appear to develop separately, although because of structural considerations the elements impinge on one another. Initially, hemodynamic changes predominate: (a) arterial dilation, (b) venular resistance is increased, (c) capillary pressure is elevated, and (d) the surface for exchange is increased through the opening up of new capillaries. Simultaneously with the vasodilation, substantial amounts of plasma protein leak into the tissue to cause manifest edema. Cellular emigration, on the other hand, is usually delayed in appearance and progresses slowly.