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It is thin and watery and contains few blood cells or other large proteins. Any fluid (solvent and solute) that has passed through a presumably normal membrane, such as the capillary wall, as a result of unbalanced hydrostatic and osmotic forces; characteristically low in protein unless there has been secondary concentration. fluid that has passed through a normal membrane as a result of imbalanced hydrostatic/onchotic (osmotic) pressures, e.g.process of oedema formation as part of acute inflammation (inflammatory exudate accumulates as net result of onchotic pressure exerted by plasma proteins that have escaped from local vessels into surrounding tissue spaces)a fluid substance that has passed through a membrane or has been extruded from a tissue; in contrast to an exudate, a transudate is characterized by high fluidity and a low content of protein, cells or solid matter derived from cells.

Transudates result from an imbalance in oncotic and hydrostatic pressures. The serous body cavities surrounding the lungs, heart and abdomen normally contain a small amount of fluid.This fluid is formed when plasma exits from a capillary bed in the tissue and enters the interstitial space.The rate of fluid formation depends on the balance between plasma and tissue oncotic and hydrodynamic pressures.Voiceover: So when we get into talking about plural effusions, that fluid that's accumulating in the actual plural space, is either a transudate or an exudate, and that can be a really confusing idea to try and wrap your head around, so let's write this just over here in the corner.We're either talking about transudate fluid, or exudate fluid.The real difference between the two is how that fluid came about to be in that space.

How did that fluid get in that space in other words. For instance if somebody has congestive heart failure, liver failure, if somebody had pneumonia, lupus, and how we really break those up is based off of two things.

Then we have our endothelial cells which are these guys poking out here.

Then these little yellow dots, these represent my proteins, so my plasma protein.

The forces promoting fluid filtration out of the blood vessels (capillaries on the arteriolar side) into the interstitium (plasma hydrodynamic pressure and tissue oncotic pressure) are slightly higher than the forces promoting fluid absorption from the tissue back into the blood vessels ( capillaries on the venule side) (plasma oncotic pressure and tissue hydrodynamic pressure).

This leads to a net accumulation of small amounts of fluid in the interstitium that enters the body cavities.

Excess fluid is normally removed by the lymphatic system.