04-24-2012, 10:40 AM   #1
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Diarrhea in I.B.D.

There are many types of diarrhea including; inflammatory, secretory, infective, bile-salt,osmotic, exudative, and increased motility diarrhea.

In I.B.D. the epithelium (thin layer of cells which line the intestine) can become extensively damaged. Loss of the epithelial lining affects absorption from the intestines. The absorptive epithelial cells (enterocytes) lining the bowel are needed in the digestive process, and for absorption of water. When these cells are damaged water is poorly absorbed, and inflammatory diarrhea results.
The immune response, seen in I.B.D., results in white cells being activated. These cells release inflammatory mediators and cytokines (as part of the defense process) which stimulate fluid secretion into the bowel (another defense mechanism, to flush the bowel.) which causes secretory diarrhea.
Further, products released by leukocytes (white cells) known as reactive oxygen species (used to kill pathogens) can damage or kill intestinal epithelial cells. These cells are replaced by immature cells that are less efficient. Immature small intestine epithelial cells don't have the brush border enzymes and transporters necessary for absorption of some nutrients, and water. So, there is less absorption of fluids. The large bowel epithelium is not as complex as that of the small bowel, but is vital for fluid absorption (and, both are involved in the immune system containing toll like receptors.)

If that isn't enough, inflammation can disturb gut motility by affecting enteric nerves. Increased motility means there may not be enough time for fluid absorption to take place. And, incomplete digestion of foods due to shorter transit times causes issues such as fermentation, which compounds the problem.
There are at least two other types of diarrhea. Bile salt diarrhea can be particularly problematic. It is a functional problem resulting from a resected terminal ileum, causing the incomplete re-absorption of bile fluids, and causing diarrhea. Osmotic diarrhea is caused by some laxatives, or from an inability to digest certain food components (such as lactose or fructose) and it also causes fluid to be drawn into the bowel.

Each issue has different treatments, however treating the I.B.D itself is the most important approach to take.

(Some people suffer constipation with I.B.D. In their case issues include reduced bowel motility, and too much water being absorbed causing hard stools.)

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