The two major forms of human inflammatory bowel disease (IBD), Crohn's disease (CD), and ulcerative colitis (UC), represent classic chronic inflammatory disorders, characterized by progressive destructive inflammation in the gastrointestinal tract. Although the majority of research into IBD pathogenesis has focused on immune dysregulation, vascular involvement has also been recognized. The intestinal microcirculation and its endothelial lining contribute to normal immune homeostasis in the gut and potentially to the chronic dysregulated inflammation, which characterizes IBD. Alterations in endothelial-leukocyte interaction have been identified in the chronically inflamed intestine, including an enhanced capacity for endothelial-leukocyte interaction. The mechanisms of altered endothelial function in IBD immune dysregulation appear to involve a diminished capacity to generate nitric oxide (NO), as well as altered expression of cell adhesion molecules and vascular addressins. In addition to its role in leukocyte recruitment, the intestinal microvasculature may also contribute to chronic inflammation through its central role in the regulation of tissue perfusion. Studies have demonstrated an altered microvascular architecture characterized by stenosis, which correlates with decreased in vivo perfusion in chronically inflamed and remodeled intestine. Recent work has demonstrated an acquired microvascular dysfunction, with impaired vasodilation in IBD involved intestinal microves-sels. Chronically inflamed IBD microvessels demonstrate a diminished endothelium-dependent vasodilatory capacity, a finding not present in uninvolved IBD gut arterioles. In summary, important alterations in IBD intestinal microvascular physiology and function have been identified in human IBD, which may contribute to chronic inflammatory and ischemic pathophysiology.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.