That requires defining an equation for the quantity ingested and present in the gut lumen:

In those models, additional compartments describe the various sections of the gut lumen and tissue.

Consequently, stool within the gut lumen becomes excessively dehydrated.

When drugs are taken orally, they enter the gut lumen to be absorbed in the small intestine and sometimes, in the stomach.

The gut lumen contains large amount of fluid, and motility, leading to diarrhea that can last for several days.

It is more active in the tissues than in the gut lumen.

In the case of gastrointestinal parasites, development may take place entirely in the gut lumen or with only limited movement into the mucosa.

The absorption of water from the gut lumen is an osmotic consequence of such processes.

At the same time the enterotoxin also promotes a net secretion of chloride ions into the gut lumen from the epithelial cells.

The consequent build up of osmotically active particles within the gut lumen inhibits water reabsorption by the gut wall.