Anatomy Involved in Crohn's Disease
Noel Williams, MD
Simmy Bank, MD, MB, ChB
Francisco Talavera, PharmD, PhD
BS Anand, MD
Venkatachala Mohan, MD
Overview of the Digestive System
The digestive system is made up of the digestive tract, which is a long series of organs, including the esophagus, the stomach, the small intestine, and the large intestine, that runs from the mouth to the anus. The digestive tract in an adult is about 30 feet long.
Digestion begins in the mouth where saliva begins to break down food. Food is swallowed from the mouth into the esophagus, which then moves the chewed food to the stomach. The stomach has strong muscular walls that mix and churn the food with acid and enzymes (known as gastric juice), breaking the food into smaller pieces. The processed semiliquid food, called chyme, is slowly released from the stomach into the small intestine.
Most digestion and absorption occurs in the small intestine. The small intestine has 3 parts: 1) the duodenum, 2) the jejunum, and 3) the ileum. Enzymes and other substances made by intestinal cells, the pancreas, and the liver are secreted into the small intestine and breakdown starches, sugars, fats, and proteins. Absorption of nutrients occurs through the millions of tiny fingerlike projections called villi and the even tinier projections on the villi called microvilli. Any undigested material moves to the large intestine. The large intestine or colon has four sections called the 1) cecum/ascending colon, 2) transverse colon, 3) descending colon/sigmoid, and 4) rectum. The main job of the large intestine is to remove water and salts (electrolytes) from the undigested material and to form solid waste (feces) that can be excreted. The remaining contents of the large intestine move to the rectum, where feces are stored until they leave the body through the anus as a bowel movement.
How the Digestive System is Involved in Crohn's Disease
Crohn's disease is a chronic inflammation of the digestive tract. Any part of the digestive tract from the mouth to the anus can be involved, although it most commonly affects the end of the small intestine called the terminal ileum and the beginning of the large intestine called the cecum. The inflammation may extend deep into the tissues of the organ that is affected. The inflammation may cause pain in the abdomen and may make the intestines empty frequently, resulting in diarrhea. Other symptoms include bloating, constipation, pain or bleeding with a bowel movement, urinary tract infection or vaginal infection.
In addition, the following complications may occur: blockage in the intestine due to thickening of the intestinal walls; ulcers or fissures may tunnel through the affected area into surrounding areas (for example, bladder, vagina, skin), and fistulas (communication between the intestine and other adjacent organs) may develop. Thickening of the wall due to acute inflammation may narrow the lumen of the small intestine. Scar tissue resulting from the healing process may also lead to a narrowed bowel, and strictures are often present. Nutritional complications are common in Crohn's disease. Protein, calorie, and vitamin deficiencies may be due to inadequate dietary intake, loss of protein in the intestine, or poor absorption. Depending on what part of the intestine is affected, the symptoms and complications may differ.
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