Gastroesophageal reflux disease (GERD), gastro-oesophageal reflux disease (GORD), gastric reflux disease, or acid reflux disease is chronic symptoms or mucosal damage caused by stomach acid coming up from the stomach into the esophagus. A typical symptom is heartburn. GERD is usually caused by changes in the barrier between the stomach and the esophagus, including abnormal relaxation of the lower esophageal sphincter, which normally holds the top of the stomach closed; impaired expulsion of gastric reflux from the esophagus, or a hiatal hernia. These changes may be permanent or temporary ("transient"). Another kind of acid reflux, which causes respiratory and laryngeal signs and symptoms, is called laryngopharyngeal reflux (LPR) or "extraesophageal reflux disease" (EERD). Unlike GERD, LPR is unlikely to produce heartburn, and is sometimes called silent reflux.

Acute pancreatitis or acute pancreatic necrosis is a sudden inflammation of the pancreas. Depending on its severity, it can have severe complications and high mortality despite treatment. While mild cases are often successfully treated with conservative measures, such as NPO (nil per os or nothing by mouth (NBM)) and aggressive intravenous fluid rehydration, severe cases may require admission to the intensive care unit or even surgery to deal with complications of the disease process.

An anal fissure is a break or tear in the skin of the anal canal. Anal fissures may be noticed by bright red anal bleeding on the toilet paper, sometimes in the toilet. If acute they may cause severe periodic pain after defecation but with chronic fissures pain intensity is often less. Anal fissures usually extend from the anal opening and are usually located posteriorly in the midline, probably because of the relatively unsupported nature of the anal wall in that location. Fissure depth may be superficial or sometimes down to the underlying sphincter muscle.

Autoimmune Hepatitis is a disease of the liver that occurs when the body's immune system attacks cells of the liver. Anomalous presentation of human leukocyte antigen (HLA) class II on the surface of hepatocytes, possibly due to genetic predisposition or acute liver infection, causes a cell-mediated immune response against the body's own liver, resulting in autoimmune hepatitis. This abnormal immune response results in inflammation of the liver, which can lead to further complications, including cirrhosis.

Barrett's esophagus (sometimes called Barrett's syndrome, CELLO—columnar epithelium lined lower oesophagus) refers to an abnormal change (metaplasia) in the cells of the inferior portion of the esophagus. A positive diagnosis generally requires observing specific macroscopic and microscopic changes. The normal squamous epithelium lining of the esophagus is replaced by metaplastic columnar epithelium. Columnar epithelium refers to a cell type that is typically found in more distal parts of the gastrointestinal system. The medical significance of Barrett’s esophagus is its strong association with esophageal adenocarcinoma, a particularly lethal cancer.

Celiac disease is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy onward. Symptoms include chronic diarrhoea, failure to thrive (children), and fatigue, but these may be absent, and symptoms in other organ systems have been described.

A growing portion of diagnoses are being made in asymptomatic persons as a result of increased screening; the condition is thought to affect between 1 in 1,750 and 1 in 105 people in the United States. Celiac disease is caused by a reaction to gliadin, a prolamin (gluten protein) found in wheat, and similar proteins found in the crops of the tribe Triticeae (which includes other common grains such as barley and rye). Upon exposure to gliadin, and specifically to three peptides found in prolamins, the enzyme tissue transglutaminase modifies the protein, and the immune system cross-reacts with the small-bowel tissue, causing an inflammatory reaction. That leads to a truncating of the villi lining the small intestine (called villous atrophy). This interferes with the absorption of nutrients, because the intestinal villi are responsible for absorption. The only known effective treatment is a lifelong gluten-free diet. While the disease is caused by a reaction to wheat proteins, it is not the same as wheat allergy.

Chronic pancreatitis is a long-standing inflammation of the pancreas that alters its normal structure and functions. It can present as episodes of acute inflammation in a previously injured pancreas, or as chronic damage with persistent pain or malabsorption.

Cirrhosis is a consequence of chronic liver disease characterized by replacement of liver tissue by fibrosis, scar tissue and regenerative nodules (lumps that occur as a result of a process in which damaged tissue is regenerated), leading to loss of liver function. Cirrhosis is most commonly caused by alcoholism, hepatitis B and C, and fatty liver disease, but has many other possible causes. Some cases are idiopathic, i.e., of unknown cause.

Colorectal cancer, commonly known as bowel cancer, is a cancer caused by uncontrolled cell growth (neoplasia), in the colon, rectum, or vermiform appendix. Colorectal cancer is clinically distinct from anal cancer, which affects the anus. Colorectal cancers start in the lining of the bowel. If left untreated, it can grow into the muscle layers underneath, and then through the bowel wall. Most begin as a small growth on the bowel wall: a colorectal polyp or adenoma. These mushroom-shaped growths are usually benign, but some develop into cancer over time. Localized bowel cancer is usually diagnosed through colonoscopy.

Colon cancer is the second leading cause of cancer deaths in the United States. Approximately 150,000 people are diagnosed with colon cancer each year. About 50,000 people will die from colon cancer yearly. Most people are diagnosed with colon cancer after age 50. Men and woman are equally likely to get colon cancer. An individual’s lifetime risk for colon cancer is about 5%. The majority of people who develop colon cancer do not have any specific risk factors for colon cancer. Environmental agents may play a role in the development of colon cancer. Our diets may promote colon cancer development. (They are high in animal fat and low in anti-oxidants and other minerals.) Genetic factors also play a role in colon cancer development. Certain diseases are linked to colon cancer (ulcerative colitis and Crohn’s disease).

Most colon cancers will develop from benign growths in our colon called polyps. There are different types of polyps. Those associated with colon cancer are called adenomas. Polyps do not usually cause any symptoms. It usually will take years for a polyp to develop into cancer. (It is estimated that it can take 10-15 years for an adenoma to develop into cancer.) Not all adenomas will develop into cancer. However, with rare exception, colon cancer will come from these adenomas. If these polyps can be detected and removed from the colon, the risk of developing colon cancer can be significantly reduced. Colonoscopy is currently the best method for detecting and removing polyps from the colon. If polyps are identified during a colonoscopy, they are usually removed during that examination. If the polyps are found to be the adenomas, there is a chance that more of these types of polyps will develop. Therefore, it is important to have periodic examinations of the colon (usually every 3-5 years).

Constipation (also known as costiveness, dyschezia, and dyssynergic defaecation) refers to bowel movements that are infrequent and/or hard to pass. Constipation is a common cause of painful defecation. Severe constipation includes obstipation (failure to pass stools or gas) and fecal impaction (Bowel obstruction).

Crohn's disease, also known as regional enteritis, is a type of inflammatory bowel disease that may affect any part of the gastrointestinal tract from mouth to anus, causing a wide variety of symptoms. It primarily causes abdominal pain, diarrhea (which may be bloody if inflammation is at its worst), vomiting (can be continuous), or weight loss, but may also cause complications outside the gastrointestinal tract such as skin rashes, arthritis, inflammation of the eye, tiredness, and lack of concentration.

Diverticulosis also known as "diverticular disease" is the condition of having diverticula in the colon, which are outpocketings of the colonic mucosa and submucosa through weaknesses of muscle layers in the colon wall. These are more common in the sigmoid colon, which is a common place for increased pressure. This is uncommon before the age of 40, and increases in incidence after that age.

Eosinophilic esophagitis is an allergic inflammatory condition of the esophagus. Symptoms are swallowing difficulty, food impaction, and heartburn. The disease was first described in children but occurs in adults as well. The condition is not well understood, but food allergy may play a significant role.

A variety of complaints are attributed to "excess gas" such as belching, bloating, abdominal pain, and flatulence. In most people with such complaints, however, the amount of measured gas in the gastrointestinal system is no greater than that found in normal asymptomatic subjects. Gas is produced in all people and is normally eliminated from the body through belching and by passing it through the anus, the latter occurring on average 10-20 per day in normal individuals.

Gastritis is an inflammation of the lining of the stomach, and has many possible causes. The main acute causes are excessive alcohol consumption or prolonged use of nonsteroidal anti-inflammatory drugs (also known as NSAIDs) such as aspirin or ibuprofen. Sometimes gastritis develops after major surgery, traumatic injury, burns, or severe infections. Gastritis may also occur in those who have had weight loss surgery resulting in the banding or reconstruction of the digestive tract. Chronic causes are infection with bacteria, primarily Helicobacter pylori, chronic bile reflux, stress and certain autoimmune disorders can cause gastritis as well. The most common symptom is abdominal upset or pain. Other symptoms are indigestion, abdominal bloating, nausea, and vomiting and pernicious anemia. Some may have a feeling of fullness or burning in the upper abdomen. A gastroscopy, blood test, complete blood count test, or a stool test may be used to diagnose gastritis.

Gastroesophageal reflux disease (GERD), gastro-oesophageal reflux disease (GORD), gastric reflux disease, or acid reflux disease is chronic symptoms or mucosal damage caused by stomach acid coming up from the stomach into the esophagus. A typical symptom is heartburn. GERD is usually caused by changes in the barrier between the stomach and the esophagus, including abnormal relaxation of the lower esophageal sphincter, which normally holds the top of the stomach closed; impaired expulsion of gastric reflux from the esophagus, or a hiatal hernia. These changes may be permanent or temporary ("transient"). Another kind of acid reflux, which causes respiratory and laryngeal signs and symptoms, is called laryngopharyngeal reflux (LPR) or "extraesophageal reflux disease" (EERD). Unlike GERD, LPR is unlikely to produce heartburn, and is sometimes called silent reflux.

Helicobacter pylori, previously named Campylobacter pyloridis, is a Gram-negative, microaerophilic bacterium found in the stomach. It was identified in 1982 by Barry Marshall and Robin Warren, who found that it was present in patients with chronic gastritis and gastric ulcers, conditions that were not previously believed to have a microbial cause. It is also linked to the development of duodenal ulcers and stomach cancer. However, over 80 percent of individuals infected with the bacterium are asymptomatic and it has been postulated that it may play an important role in the natural stomach ecology. Like many infections, H. pylori infection occurs after an individual swallows the bacterium after contact with an individual who is infected or with utensils or food contaminated with it. The rate of infection increases with age and is more common at younger ages in developing countries due to poor sanitation and crowded living conditions. Nevertheless even in the United States, it is estimated that half of people have the infection by age 60.

Hemorrhoids, are vascular structures in the anal canal which help with stool control. They become pathological or piles when swollen or inflamed. In their physiological state they act as a cushion composed of arterio-venous channels and connective tissue that aid the passage of stool. The symptoms of pathological hemorrhoids depend on the type present. Internal hemorrhoids usually present with painless rectal bleeding while external hemorrhoids present with pain in the area of the anus.

Hepatitis C is an infectious disease primarily affecting the liver, caused by the hepatitis C virus (HCV). The infection is often asymptomatic, but chronic infection can lead to scarring of the liver and ultimately to cirrhosis, which is generally apparent after many years. In some cases, those with cirrhosis will go on to develop liver failure or other complications, including liver cancer or life-threatening esophageal varices and gastric varices. The hepatitis C virus is spread by blood-to-blood contact. Most people have few, if any symptoms after the initial infection, yet the virus persists in the liver in about 85% of those infected. Persistent infection can be treated with medication; peginterferon and ribavirin are the current standard therapy. Overall, between 51-80% of treated patients are cured. Those who develop cirrhosis or liver cancer may require a liver transplant, and the virus universally recurs after transplantation. An estimated 180 million people worldwide are infected with hepatitis C. Hepatitis C is not known to cause disease in other animals. No vaccine against hepatitis C is currently available.

Irritable bowel syndrome (IBS, or spastic colon) is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements. Diarrhea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C or IBS-A, respectively). IBS may begin after an infection (post-infectious, IBS-PI), a stressful life event, or onset of maturity without any other medical indicators. Although there is no cure for IBS, there are treatments that attempt to relieve symptoms, including dietary adjustments, medication and psychological interventions. Patient education and a good doctor-patient relationship are also important.

Steatohepatitis (also known as fatty liver disease) is a type of liver disease, characterized by inflammation of the liver with concurrent fat accumulation in liver ("steato", meaning fat, "hepatitis", meaning inflammation of the liver). Mere deposition of fat in the liver is termed steatosis, and together these constitute fatty liver changes. Classically seen in alcoholics as part of alcoholic liver disease, steatohepatitis also is frequently found in people with diabetes and obesity and it is related to metabolic syndrome. When not associated with excessive alcohol intake, it is referred to as non-alcoholic steatohepatitis, or NASH and is the progressive form of the relatively benign Non-alcoholic fatty liver disease. Steatohepatitis of either etiology may progress to cirrhosis, and NASH is now believed to be a frequent cause of unexplained cirrhosis (at least in Western societies). NASH is also associated with Lysosomal Acid Lipase Deficiency.

Ulcerative colitis (Colitis ulcerosa, UC) is a form of inflammatory bowel disease (IBD). Ulcerative colitis is a form of colitis, a disease of the intestine, specifically the large intestine or colon, that includes characteristic ulcers, or open sores, in the colon. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset. IBD is often confused with irritable bowel syndrome (IBS), a troublesome, but much less serious, condition. Ulcerative colitis has similarities to Crohn's disease, another form of IBD. Ulcerative colitis is an intermittent disease, with periods of exacerbated symptoms, and periods that are relatively symptom-free. Although the symptoms of ulcerative colitis can sometimes diminish on their own, the disease usually requires treatment to go into remission.