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There is a balance between hydrostatic forces, which tend to make
fluid pass out from the capillaries to the interstitium and alveoli,
and oncotic forces, which draw fluid in to the capillary bed from
the interstitium.
Hydrostatic pressure predominates on the arterial
side of the capillary and oncotic pressure on the venous side. In
hydrostatic edema , the hydrostatic forces dominate, and the fluid
is forced into the interstitium of the lung and alveolar spaces.
When epithelial damage occurs, the normal tight junctions of
epithelial cells are lost and fluid flows freely into alveolar
spaces. When there is endothelial damage, the barrier function of
the capillary wall is also impaired. |
