Significance of Protein in Edema Fluids

Abstract

The partition of extracellular fluid between plasma and tissues is largely regulated
by the balance of hydrostatic an~ colloid osmotic (oncotic) pressure gradients across
capillary membranes. Normally ~ small excess of tissue fluid forms, enters lymphatics
and returns to the bloodstream. When an imbalance develops between the rate of lymph
production and the rate of its return to the systemic venous circulation, edema.or effusion
appear. Accumulation of edema, however, is not uniform in amount and composition
throughout the body and depend, on the forces governing capillary filtration, regional
differences in capillary permeabiFty, lymph flow and the specific factor tending to perpetuate
the edema. Obstruction td lymph return or disruption of capillary integrity (e.g.
I
infiltrating cancer or inflammation) promote effusion or edema high in protein content
(so-called "exudate"). On the other hand, increased hydrostatic pressure in semipermeable
capillaries promotes excess lymph and ultimately edema or effusion low in protein
content (so-called "transudate"). iThe hepatic sinusoid is unique in its free permeability
to plasma protein. Hepatic venous outflow obstruction, accordingly, produces excess
hepatic and thoracic duct lymphi and eventually ascitic fluid, high in protein.