The Osmosis Unit

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The Starling hypothesis of fluid exchange

The Starling hypothesis of fluid exchange was put forward in 1896. It suggested that the main function of the circulatory system was to deliver food and gasses to the cells and remove waste products. Capillary fluid balance and exchange are central to this process. Ernst Starling published his fluid exchange theory in 1896 (fig 1). He suggested that the arterial capillary pressure was greater than the arterial osmotic pressure which resulted in fluid movement out of the capillary. At the venous end of the capillary he suggested that the venous pressure was less than the osmotic pressure resulting in fluid movement back into the capillary. Fluid balance was achieved when the volume filtered out at the arterial end was  equal to the volume osmotically reabsorbed at the venous end (fig 1).

There are two major problems with this hypothesis;

1 The osmotic pressure is not constant down the length of the capillary

2 Capillary flow is pulsatile

These problems are discussed below.

Probelms with the Starling Hypothesis

Pulsatility in the capillary

PRO as a new theory of fluid exchange

The therapeutic significance of PRO




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Last modified: 07/05/06