GI Tract Guide
The gastrointestinal (GI) tract is the passageway of the digestive system that runs from the mouth to the anus, carrying food and liquids from ingestion, digestion, and absorption to evacuation through feces. This interactive guide will help you learn about the organs that make up the GI tract and how they can be impacted by Crohn’s disease and ulcerative colitis.
How to Use the Guide
Click the + hotspots for a detailed view of the GI tract, including the location and function of each organ and how they may be affected by IBD.
Start exploringEsophagus
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The esophagus transports food from the mouth, through the throat, and into the stomach.
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It is rare for Crohn's disease to affect the esophagus.
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A fungal infection called thrush can develop in the esophagus, especially after antibiotics or corticosteroid use.
Stomach
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The main function of the stomach is digestion. Digestion occurs when muscle contractions and secreted acids and digestive enzymes break down food.
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It is rare for Crohn's disease to affect the stomach.
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Gastritis (inflammation of the stomach) can occur for several reasons, including as a result of medications (e.g., steroids, ibuprofen, oral iron) and/or infections.
Proximal Small Bowel (Duodenum and Jejunum)
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The duodenum is the first part of the small bowel. It receives digested food particles from the stomach and secretions from both the pancreas and bile ducts to help with digestion.
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The jejunum connects the duodenum to the ileum and is primarily responsible for the absorption of nutrients.
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Crohn’s disease may affect the small bowel which can result in:
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Inflammation, causing pain and poor absorption of vitamins and micronutrients.
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Strictures (narrowing of the bowel) causing pain, bowel obstruction, nausea and/or vomiting.
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Formation of fistulas (abnormal connections between two organs) into other portions of the small bowel or the colon. Symptoms are not always present.
Ileum
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The ileum is the third part of the small intestine. A function of the ileum is to absorb vitamin B12. Some people with IBD may need supplementation with vitamin B12 after surgery if part of their ileum is removed.
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The ileum also absorbs bile acids, which are involved in fat absorption and elimination of undigested food.
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Patients who have had a partial or complete surgical removal of their ileum may experience diarrhea due to excess bile acids entering the colon.
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Imaging tests, including CT, MRI, or small bowel series, provide a way to locate areas of inflammation, narrowing, or fistulas. Read more about the different tests used to diagnose and monitor IBD.
Terminal Ileum
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The terminal ileum is the end of the small bowel and connects to the beginning of the colon (cecum).
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This area can develop strictures (narrowings) due to chronic inflammation and fibrosis (scarring of the intestine).
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The terminal ileum is the most common site for inflammation and the most frequently involved area that requires resection (surgical removal) in Crohn’s patients.
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Mild redness/irritation in the terminal ileum may occur in patients with pancolitis (inflammation affecting the entire colon) and is known as backwash ileitis.
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Backwash ileitis is different from the ileal inflammation that can be seen in Crohn’s disease. It does not indicate a change of diagnosis from ulcerative colitis to Crohn’s disease.
Ileocecal Valve
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The ileocecal valve separates the colon from the small bowel.
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A marker of the beginning of the colon, it is frequently photographed during a colonoscopy.
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This valve is frequently removed in patients with Crohn's disease because it can become fibrotic (scarred) and strictured (narrowed) for those with longstanding or aggressive disease. Occasionally, this narrowing may be treated during a colonoscopy with dilation, which stretches the valve to make it wider.
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Some patients with ulcerative colitis have wide, gaping ileocecal valves due to scar tissue.
Appendix
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The appendix is located in the cecum (the first part of the colon).
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Exact physical function is not known and surgical removal causes no observable complications.
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There is no association between surgical removal of the appendix (appendectomy) and developing Crohn's disease.
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In left-sided ulcerative colitis, or proctitis, there may be inflammation surrounding the internal opening of the appendix known as a cecal red patch.
Cecum
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The cecum is the beginning of the colon and is connected to the small bowel (terminal ileum).
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The cecum and the terminal ileum, are the parts of the digestive tract most frequently affected by Crohn’s disease.
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In extensive colitis or pancolitis, the inflammation extends from the rectum to the cecum.
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In left-sided ulcerative colitis, or proctitis, there may be inflammation surrounding the internal opening of the appendix known as a cecal red patch.
Ascending Colon
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The ascending colon is the first section of the colon located between the cecum and the transverse colon (second part of the colon).
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The ascending colon absorbs remaining water and other key nutrients from indigestible material, solidifying it to form stool.
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The ascending colon may or may not be involved in patients with Crohn’s disease due to the patchy nature of Crohn’s disease.
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Pancolitis or extensive colitis causes inflammation of the entire colon, including the ascending colon.
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Left-sided ulcerative colitis will not involve this area.
Descending Colon
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The descending colon's main job is to store stool that will ultimately empty into the rectum.
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The descending colon is located on the left side of the abdomen.
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May be affected by Crohn’s disease in the form of inflammation, fistulas (abnormal connections between two organs), or strictures.
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The descending colon is often involved in patients with ulcerative colitis; this is often known as left-sided colitis.
How to Use the Guide
Click the + hotspots for a detailed view of the GI tract, including the location and function of each organ and how they may be affected by IBD.
Start exploringRectum
- purple Crohn's Disease
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The rectum is at the end of the colon, and is connected to the anus. The rectum is a holding area for stool, which sends a signal to the brain that it is time to have a bowel movement.
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Rectal inflammation associated with Crohn’s disease can lead to the development of fistulas (abnormal connections between the rectum, skin, or adjacent organs).
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The rectum is almost always involved in ulcerative colitis.
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Rectal inflammation, associated with ulcerative colitis, may cause rectal pain, urgency, and tenesmus (a frequent urge to have a bowel movement but nothing comes out or it is incomplete).
Anus
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The anus is the external opening at the end of the digestive tract where waste is eliminated.
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Fissures, tears in the lining of the anal canal, can be seen in Crohn’s disease. Symptoms include anal pain, spasms, and bleeding.
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A perianal fistula (abnormal connection) between the anal canal and skin may occur in Crohn’s disease patients.
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Abscesses (infected, pus-filled cavities) may form between the anal canal and the skin in Crohn’s patients with perianal disease. Treatment requires drainage of the abscess cavity.
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Anal skin tags may be seen in Crohn’s patients and may be the result of a chronic anal fissure. They are typically not painful unless infected or irritated due to frequent wiping. Surgery to remove skin tags is not recommended because healing can be difficult.
Internal Hemorrhoids
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Internal hemorrhoids are normal blood vessels located at the bottom of the lower rectum. The vessels are typically not sensitive to touch, pain, or temperature.
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Internal hemorrhoids become symptomatic when the connective tissue that holds them together weakens. This occurs most commonly with age, but can be seen with pregnancy, straining, and sitting for long periods of time.
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Treatment is symptom-based and rarely involves surgery.
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In IBD patients, there may be an increased risk of poor wound healing if hemorrhoids are surgically removed.
External Hemorrhoids
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External hemorrhoids are normal blood vessels located at the bottom of the lower rectum.
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External hemorrhoids are covered by skin tissue and become symptomatic when there is a breakdown of the surrounding connective tissue.
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Symptoms can include sensitivity to touch, temperature, and pain when sitting or during bowel movements. Hemorrhoids can also bleed.
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Treatment is symptom-based and rarely involves surgery.
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Hemorrhoids can become irritated from the frequent bowel movements or straining experienced by IBD patients. There may be an increased risk of poor wound healing if hemorrhoids are surgically removed.
Internal Anal Sphincter
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Located at the beginning of the anal canal, this muscle contracts to prevent the escape of stool and relaxes to allow its release. It can be damaged by anal surgery, childbirth, or fistula.
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A fistula (abnormal connection) can travel through this area and is defined based upon the nearness to the sphincter muscle.
External Anal Sphincter
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Located at the end of the anal canal, this muscle contracts to keep the canal and opening closed to prevent the escape of stool and relaxes to allow its release. It can be damaged by anal surgery, childbirth, or fistula.
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Fistulas (abnormal connections) can travel through this area.
Anal Glands
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Anal glands are small sacs that line the wall of the anal canal and drain to anal crypts ending in the space between the internal and external sphincters. Anal glands secrete material into the anal canal via the anal duct.
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If anal glands become inflamed and blocked from Crohn's disease, a fistula (abnormal connection) or perianal abscess can form.
Anal Crypts
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Anal crypts are the innermost parts of the anal glands.
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Blockage of anal crypts may lead to fistulas (abnormal connections) or abscesses.
Anal Canal and Dentate Line
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The anal canal includes the end of the rectum above the anus.
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The dentate line divides the upper and lower portions of the anal canal.
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Blood and nerve supply is different above and below this line. The upper portion of the anal canal is above the dentate line and does not feel pain. The lower portion, which is similar to the skin, can perceive pain signals.