Edema, inflammatory
Chapter: 2
Edema is an early component of a developing inflammatory lesion. It occurs due to increased vascular permeability that allows plasma proteins to escape from the circulation locally. Their presence increases oncotic (osmotic) pressure extravascularly, which tends to increase the loss of fluid from the leaky vessels. Because of these facts, inflammatory edema fluid will almost always have a specific gravity >1.015. Increased vascular permeability, coupled with egress of plasma proteins into the extravascular space, collectively are very important in the earliest phases of an inflammatory reaction: increased flow of fluid through the lesion into the lymphatics may help to flush away the inciting stimulus and, more important, the plasma protein precursors of inflammatory mediators are almost immediately made available to begin expanding and augmenting the inflammatory response.