Oedema

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Oedema means that too much fluid, mainly water, has accumulated in the body. The term comes from a Greek word meaning â€˜a swollen conditionâ€™.

The accumulation of fluid may be in a particular location or it may be in several places in the body. In generalised oedema, fluid accumulates in any of the tissues, but especially in the air spaces of the lungs and in the spaces in the abdomen surrounding the bowels and other organs (the peritoneal cavity). Localised oedema is usually temporary and often corrects itself. Generalised oedema, however, is almost always abnormal and requires specific treatment.

The body is made of millions of cells, most of them linked together to form tissues. The cells themselves are largely filled with (and surrounded by) fluid. So a considerable proportion of the body weight - about 60 per cent - consists of water.

The processes that result in the movement of water into and out of cells are important in human body function. Also important are the factors that control the total amount of water in the body at any particular time. For example, in a healthy person without oedema, the kidneys deal with surplus fluid in the body by disposing of it in the urine.

The amount of water normally remaining in the body is provided by the difference between fluid taken in and fluid discharged. Fluid is taken into the body by drinking, food, and by water produced by bodily processes. It is discharged from the body via urine, faeces, non-visible perspiration (for example, when breathing out), and sweat.

Factors affecting the quantity of water in the body include high surrounding temperatures and taking strenuous exercise. In healthy people, such factors usually result in a significant increase in the intake of fluid, which is almost immediately compensated for by an increase in the urinary output.