Answer: vascular walls in the bloodstream
Explanation:
Edema is the accumulation of fluid in the extracellular or interstitial space, in addition to the body's cavities. It is a sign that appears in many diseases and manifests itself as a swelling of the soft tissues due to the accumulation of fluid in the interstitial compartment. This edema can be seen locally as it happens in the lower extremities or as a generalised feeling of swelling (hands, abdomen).
<u>Edema occurs if there is an imbalance between the forces that regulate the passage of fluid from one compartment to another</u>. If there is abundant water flow from the intravascular to the interstitial compartment, an edema occurs. Such fluid extravasation may respond to physical or chemical factors, <u>from an increase in intravascular pressure in the return circulation, to an increase in the permeability of the vascular wall, or a decrease in the levels of molecules that maintain intravascular fluid, caused by proteins</u>.
So an edema is produced by an imbalance in the forces that regulate the passage of fluid from one compartment to another in the tissues.