Pathogenesis of edematous states

Edema is a clinical sign reflecting an increased volume of sodium and water in the interstitial space. Two types of abnormal renal sodium handling have been described in edema forming states. In the first, a primary disturbance in renal function leads to sodium retention, plasma volume expansion and, ultimately, edema formation. This type of edema is called primary edema, an "over-flow" or "nephritic" edema. By contrast, in the other type of edema, renal sodium retention seems to be attributable to a decreased effective arterial blood volume. This is "underfill" or "nephrotic" edema.