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An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as sap or blood. In the case of blood it will contain some or all plasma proteins, white blood cells, platelets, and in the case of local vascular damage: red blood cells. In plants, it can be a healing and defensive response to repel insect attack, or it can be an offensive habit to repel other incompatible or competitive plants. Organisms that feed on exudate are known as exudativores; for example, the Vampire Bat exhibits hematophagy, and the Pygmy marmoset is an obligate gummivore (primarily eats tree gum).
In humans, exudate can be a pus-like or clear fluid. When an injury occurs, leaving skin exposed, it leaks out of the blood vessels and into nearby tissues. The fluid is composed of serum, fibrin, and white blood cells. Exudate may ooze from cuts or from areas of infection or inflammation.
Plant exudates include saps, gums, latex, resin, and sometimes nectar is considered an exudate. Plant roots exude a variety of molecules into the rhizosphere, including acids, sugars, polysaccharides and ectoenzymes; this can account for 40% of root carbon. Exudation of these compounds has various benefits to the plant and to the microorganisms of the rhizosphere.
|Transudate vs. exudate|
|Main causes||Increased hydrostatic|
|Specific gravity||< 1.012||> 1.020|
|Protein content||< 25 g/L||> 29 g/L|
|< 0.5||> 0.5|
with blood albumin
|> 1.2 g/dL||< 1.2 g/dL|
upper limit for serum
|< 0.6 or < ⅔||> 0.6 or > ⅔|
|Cholesterol content||< 45 mg/dL||> 45 mg/dL|
There is an important distinction between transudates and exudates. Transudates are caused by disturbances of hydrostatic or colloid osmotic pressure, not by inflammation. They have a low protein content in comparison to exudates. Medical distinction between transudates and exudates is through the measurement of the specific gravity of extracted fluid. Specific gravity is used to measure the protein content of the fluid. The higher the specific gravity, the greater the likelihood of capillary permeability changes in relation to body cavities. For example, the specific gravity of the transudate is usually less than 1.012 and a protein content of less than 2 g/100 mL (2 g%). Rivalta test may be used to differentiate an exudate from a transudate. It is not clear if there is a distinction in the difference of transudates and exudates in plants.