Inflammatory Bowel Disease

Inflammatory bowel disease, or IBD for short, is a chronic condition that causes inflammation and ulceration in the intestinal tract. The two major types of IBD are Crohn disease, or CD, and ulcerative colitis, or UC.

Okay, so, the gastrointestinal tract is a hollow tube that includes the oral cavity, pharynx, esophagus, stomach, small and large intestines, and anus. Now, zooming in on a cross section of the intestines, we can see that the walls are typically made up of the same four layers of tissue. From the inside out, there’s the mucosa, the inner lining that consists of mucosal epithelium, connective tissue, and smooth muscle that secretes mucus and digestive enzymes. It also serves as a highly selective barrier, that absorbs nutrients and water while preventing absorption of harmful substances and bacteria.

Moving outward, the submucosa is a dense layer of tissue that provides support and contains blood vessels, lymphatics, and nerves. Next is the muscularis, which consists of a network of nerve fibers and layers of smooth muscle that contract to move intestinal contents forward in a process called peristalsis. And finally, the outermost layer is the serosa, composed of connective tissue. It anchors the intestines in place and secretes a lubricating fluid that promotes smooth movement of the intestines within the abdominal cavity.

Now, the exact cause of IBD is unknown; however, it’s likely that a combination of genetic, environmental, and immune factors alters the protective barrier function of the mucosal epithelium, leading to a dysregulated immune response. On top of that, the normal gut microbiome may also be altered, resulting in an increasing population of potentially pathogenic bacteria.

Risk factors include having a family history of IBD; dietary patterns such as a diet high in processed foods; and having another autoimmune disease. Interestingly, nicotine use increases the risk and disease severity of CD, while it’s associated with later onset and less disease severity of UC.

IBD occurs due to autoimmune activity, which is when the immune system attacks its own tissues causing inflammation and tissue damage. In UC, inflammation affects the large intestine, often starting in the rectum and spreading from there in a continuous fashion, damaging the mucosa and submucosa. The mucosa becomes fragile and small hemorrhages occur; and as the disease progresses these hemorrhagic areas coalesce into ulcers.