Pathophysiology

It begins in the rectum (proctitis) and spreads proximally along the entire colon (pancolitis) in a continuous fashion.
The mucosa of the rectum and the colon is hyperemic and edematous in the affected area.
Multiple abscesses develop in the crypts of Lieberkuhn (intestinal glands).
As the disease advances, the abscesses break through the crypts into the submucosa, leaving ulcerations.
These ulcerations destroy the mucosal epithelium, causing bleeding and diarrhea – the loss of fluid and electrolytes caused by the decreased mucosal surface are for absorption.
Protein loss through the stool is also evidenced due to breakdown of cells.
Areas of inflamed mucosa can form pseudopolyps, tonguelike projections into the bowel lumen.
Granulation tissue develops, and the mucosa musculature becomes thickened, shortening the colon.

It is characterized by inflammation of segments of the GI tract.
It can affect any part of the GI tract
- Most often seen in the terminal ileum and the colon.
- Involvement of the esophagus, the stomach, or the duodenum is uncommon.
T-helper cell cytokines such as interleukin-12 and tumor necrosis factor (TNF) stimulate the inflammatory response, which begins in the intestinal submucosa and extends to all the layers of the bowel wall.
Activated neutrophils and macrophages promote inflammation and cause tissue injury.
The inflammation can affect some segments of the intestine but not others resulting in discontinuous skip lesions.
Ulcerations are deep and longitudinal and penetrate between islands of inflamed edematous mucosa, causing the classic cobblestone appearance.
Thickening of the bowel wall occurs, as well as narrowing of the lumen with stricture development – promotes obstruction.
Abscesses or fistula tracts that communicate with other loops of bowel, the skin, the bladder, the rectum or the vagina may develop.
Histologically, granulomas are present in 50% of clients and may be located in any layer of the bowel wall – giving the affected area a cobblestone appearance.

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Inflammatory Bowel Disease