Edema is accumulation of excessive water in body cavities or interstitial tissues.

Definition of Edema = abnormal accumulation of water in tissues or body cavities

Gross characteristics of edema include:

  • Swollen, usually soft and doughy, distended tissue that tends to gravitate ventrally
  • Edematous tissue pits on pressure and the indentations remain after the pressure is removed
  • Edematous tissue is cool to the touch rather than warm (unless inflammation is also present)
  • The edematous tissue is not reddened (not hyperemic) or painful (again, unless inflammation is also present)
  • Distended lymphatics are often visible in edematous lesions
  • At postmortem examination, edema is recognized by the presence of clear yellow-tinged fluid that distends loose connective tissues or accumulates in body cavities such as the peritoneal, pleural, or pericardial spaces. The fluid may flow upon cutting through the tissue or, if the vessels were damaged sufficiently that clotting proteins accompanied the fluid, it may form a yellowish jello-like clot.

Here is a pig that was suffering from "edema disease," which is due to a septicemia of certain strains of E. coli. These bacteria produce a toxin that acts on endothelial cells, allowing fluid to leak out.

Eyelid is a favored spot for this edema to be manifest. This pig can't even open its eye because the lid is so swollen with edema fluid.

BY THE WAY, the word for eyelid edema is CHEMOSIS. Add that to your ever-expanding lexicon!

Microscopic features of edema include:

  • separation of tissue elements by spaces that are either clear (if the edema is protein-poor) or pink (if the edema fluid has abundant protein).
  • dilation of lymphatics

Histologically, edema fluid fills areas that are not supposed to have fluid. Here is a section of lung - protein-rich fluid has leaked out of the vessels and is filling alveoli and bronchioles (*).

This is bad nooz. Can't do no air exchange if there is fluid in these spaces....

Here is another photomicrograph of edema. In this case, the submucosa of the gut, which is represented by the bottom two-thirds of the photo, is markedly distended by fluid.

The arrowhead demonstrates a lymphatic which is also way big. With all this expansion, the nutrients and oxygen just have a heck of a time diffusing through to where they need to go.

This horse had a Salmonella infection, and this bug likes to damage the blood vessels of the gut - EDEMA (and much much more unfortunately).

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