What does edema refer to?

Edema refers specifically to the accumulation of excess fluid in the interstitial spaces of tissues, which leads to noticeable swelling. This condition can occur for various reasons, including inflammation, injury, or lymphatic obstruction, and occurs when the balance between fluid filtration out of the capillaries and fluid reabsorption back into them is disrupted.

In contrast, the other options reflect different concepts within the context of body fluid dynamics and the lymphatic system. Fluid accumulation in blood vessels pertains to conditions like congestion or hyperemia, not edema itself. Fluid drainage via lymphatic vessels refers to a normal function of the lymphatic system, where excess interstitial fluid is returned to the bloodstream, effectively preventing edema. Lastly, inflammation of lymph nodes is an immune response to infection or disease, which may or may not be associated with edema, but is not defined by it. Thus, the correct definition of edema is directly linked to excess tissue fluid leading to swelling.