Barrett Esophagus (BE) is the only known precursor of esophageal adenocarcinoma (EAC), which is rapidly increasing in incidence. BE involves intestinal metaplasia — the replacement of squamous epithelium by columnar epithelium — in the distal esophagus as an adaptive response to gastroesophageal reflux. Download Image

Celiac disease was historically defined as an immune-mediated enteropathy that is driven by the ingestion of dietary gluten. However, celiac disease is increasingly recognized as a systemic disorder characterized by diverse extraintestinal manifestations. Download Image

Constipation is used to describe a variety of symptoms, including hard stools, excessive straining, infrequent bowel movements, bloating and abdominal pain. Chronic constipation can occur secondary to treatment (such as opioid pain medication), systemic illness (such as Parkinson disease), local pathology (such as colorectal cancer) or, more frequently, can be the result of a primary disturbance of colonic propulsion or rectal emptying. Download Image

Chronic pancreatitis is characterized by chronic inflammation of the pancreas that results in progressive scarring and atrophy of the pancreatic tissue, pain, maldigestion (exocrine pancreatic insufficiency), diabetes mellitus (endocrine dysfunction) and increased risk of pancreatic cancer. Download Image

Clostridium difficile is an obligate anaerobic Gram-positive bacterium that is the leading cause of health-care associated infective diarrhoea. Antibiotic exposure during hospitalization and older age (>60 years) are major risk factors for developing C. difficile infection (CDI). Download Image

Colonic diverticular disease (referred to as diverticular disease) — characterized by sac-like protrusions (diverticula) on the wall of the large intestine — can be asymptomatic (known as diverticulosis) or symptomatic (such as diverticulitis or diverticular hemorrhage). Download Image

Crohn’s disease (CD) is a type of inflammatory bowel disease that can affect any part of the gastrointestinal tract and that has a chronic, progressive and destructive course. Download Image

Food allergy is an umbrella term that describes many clinical entities. However, the common mechanism of food allergy is the breakdown of clinical and immunological tolerance against ingested foods. Its most-severe form — anaphylaxis — is immediate, can involve several organ systems and can induce life-threatening hypovolemic shock and respiratory compromise. Download Image

Functional dyspepsia is a common functional gastrointestinal disorder that is characterized by discomfort or pain in the upper abdomen with no apparent organic cause. The three subtypes of the condition are: postprandial distress syndrome (PDS), epigastric pain syndrome (EPS) and a subtype with features of both PDS and EPS. Download Image

Gastro-oesophageal reflux disease (GERD) is a common disorder in adults and children. Patients usually present with heartburn and/or regurgitation but GERD can have various other atypical and extra-oesophageal manifestations. Download Image

Gastrointestinal (GI) pain — a form of visceral pain — is a common symptom of some GI disorders, such as Crohn’s disease, chronic pancreatitis and irritable bowel syndrome (IBS). Download Image

Gallstones — masses in the gallbladder or biliary tract — are found in 10–20% of the adult population, >20% of those will develop symptoms or complications. Download Image

Gastroparesis is a chronic disorder of the stomach, which is characterized by the delayed gastric emptying of solid food. The key symptoms of gastroparesis include early satiety, postprandial fullness, nausea, vomiting, upper abdominal pain, belching and bloating. Download Image

Helicobacter pylori infection causes several gastroduodenal disorders, most commonly chronic gastritis, which can progress to peptic ulcer, gastric cancer or, rarely, gastric mucosa-associated lymphoid tissue lymphoma. Unique properties of the bacterium enable colonization of the gastric epithelium. Download Image

Hookworms are soil-transmitted nematodes. Necator americanus and Ancylostoma duodenale are the predominant human parasites; they can reside in the small bowel for years, where they feed on the host’s blood, causing iron deficiency anaemia in some individuals. Download Image

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder and is not associated with structural or biochemical abnormalities in the gut. Gastrointestinal symptoms include abdominal pain or discomfort, stool irregularities and bloating. In addition, IBS is often associated with somatic comorbidities (for example, pain syndromes, overactive bladder and migraine), psychiatric conditions (including depression and anxiety) and visceral sensitivity. Download Image

Microscopic colitis (MC) is an inflammatory bowel disease affecting the large intestine that is associated with persistent watery diarrhoea, urgency and faecal incontinence. MC is characterized by a normal-appearing colonic mucosa on endoscopy and can be classified into lymphocytic colitis and collagenous colitis on histology. Download Image

Nonalcoholic fatty liver disease (NAFLD) is a consequence of systemic insulin resistance. The liver accumulates abnormal amounts of fat (nonalcoholic fatty liver (NAFL)) in the absence of excess alcohol intake. In the setting of hepatocyte injury and inflammation, nonalcoholic steatohepatitis (NASH) can progress to fibrosis and cirrhosis. Download Image

Periodontal diseases include various inflammatory conditions of the tissues that support the teeth (the gingiva, ligament and bone). Periodontal disease typically starts as gingivitis (inflammation of the gingiva) and, if untreated, can escalate to chronic periodontitis, which can lead to tooth loss. Download Image

Psoriasis is a chronic, immune-mediated disorder with a strong genetic basis. Characteristic cutaneous manifestations are red, raised scaly plaques and sometimes pustules. Systemic comorbidities can be rheumatological (psoriatic arthritis) and cardiovascular. Download Image

Ulcerative colitis (UC) is an inflammatory bowel disease characterized by long-lasting inflammation, originating in the rectum, which extends proximally in a continuous fashion to the colon. In UC, the inflammation is restricted to the innermost (mucosal) layer of the intestine, resulting in ulceration and bloody diarrhoea. Download Image

The whipworm Trichuris trichiura and the roundworm Ascaris lumbricoides are soil-transmitted helminths (STHs). These gastrointestinal parasites cause the neglected tropical diseases trichuriasis and ascariasis, respectively. Download Image