Gastrointestinal disease

The small intestine consists of the duodenum, jejunum and ileum. Inflammation of the small intestine is called enteritis, which if localised to just part is called duodenitis, jejunitis and ileitis, respectively. Peptic ulcers are also common in the duodenum.[5]^{: 879–884}

Chronic diseases of malabsorption may affect the small intestine, including the autoimmune coeliac disease, infective tropical sprue, and congenital or surgical short bowel syndrome. Other rarer diseases affecting the small intestine include Curling's ulcer, blind loop syndrome, Milroy disease and Whipple's disease. Tumours of the small intestine include gastrointestinal stromal tumours, lipomas, hamartomas and carcinoid syndromes.[5]^{: 879–887}

Diseases of the small intestine may present with symptoms such as diarrhoea, malnutrition, fatigue and weight loss. Investigations pursued may include blood tests to monitor nutrition, such as iron levels, folate and calcium, endoscopy and biopsy of the duodenum, and barium swallow. Treatments may include renutrition, and antibiotics for infections.[5]^{: 879–887}

Abdominal X-rays may be used to visualise the large intestine.

Diseases that affect the large intestine may affect it in whole or in part. Appendicitis is one such disease, caused by inflammation of the appendix. Generalised inflammation of the large intestine is referred to as colitis, which when caused by the bacteria Clostridium difficile is referred to as pseudomembranous colitis. Diverticulitis is a common cause of abdominal pain resulting from outpouchings that particularly affects the colon. Functional colonic diseases refer to disorders without a known cause, including irritable bowel syndrome and intestinal pseudoobstruction. Constipation may result from lifestyle factors, impaction of a rigid stool in the rectum, or in neonates, Hirschprung's disease.[5]^{: 913–915}

Diseases affecting the large intestine may cause blood to be passed with stool, may cause constipation, or may result in abdominal pain or a fever. Tests that specifically examine the function of the large intestine include barium swallows, abdominal x-rays, and colonoscopy.[5]^{: 913–915}

Diseases affecting the rectum and anus are extremely common, especially in older adults. Hemorrhoids, vascular outpouchings of skin, are very common, as is pruritus ani, referring to anal itchiness. Other conditions, such as anal cancer may be associated with ulcerative colitis or with sexually transmitted infections such as HIV. Inflammation of the rectum is known as proctitis, one cause of which is radiation damage associated with radiotherapy to other sites such as the prostate. Faecal incontinence can result from mechanical and neurological problems, and when associated with a lack of voluntary voiding ability is described as encopresis. Pain on passing stool may result from anal abscesses, small inflamed nodules, anal fissures, and anal fistulas.[5]^{: 915–916}

Rectal and anal disease may be asymptomatic, or may present with pain when passing stools, fresh blood in stool, a feeling of incomplete emptying, or pencil-thin stools. In addition to regular tests, medical tests used to investigate the anus and rectum include the digital rectal exam and proctoscopy.

Hepatic diseases refers to those affecting the liver. Hepatitis refers to inflammation of liver tissue, and may be acute or chronic. Infectious viral hepatitis, such as hepatitis A, B and C, affect in excess of (X) million people worldwide. Liver disease may also be a result of lifestyle factors, such as fatty liver and NASH. Alcoholic liver disease may also develop as a result of chronic alcohol use, which may also cause alcoholic hepatitis. Cirrhosis may develop as a result of chronic hepatic fibrosis in a chronically inflamed liver, such as one affected by alcohol or viral hepatitis.[5]^{: 947–958}

Liver abscesses are often acute conditions, with common causes being pyogenic and amoebic. Chronic liver disease, such as cirrhosis, may be a cause of liver failure, a state where the liver is unable to compensate for chronic damage, and unable to meet the metabolic demands of the body. In the acute setting, this may be a cause of hepatic encephalopathy and hepatorenal syndrome. Other causes of chronic liver disease are genetic or autoimmune disease, such as hemochromatosis, Wilson's disease, autoimmune hepatitis, and primary biliary cirrhosis.[5]^{: 959–963, 971}

Acute liver disease rarely results in pain, but may result in jaundice. Infectious liver disease may cause a fever. Chronic liver disease may result in a buildup of fluid in the abdomen, yellowing of the skin or eyes, easy bruising, immunosuppression, and feminization.[11] Portal hypertension is often present, and this may lead to the development of prominent veins in many parts of the body, such as oesophageal varices, and haemorrhoids.[5]^{: 959–963, 971–973}

In order to investigate liver disease, a medical history, including regarding a person's family history, travel to risk-prone areas, alcohol use and food consumption, may be taken. A medical examination may be conducted to investigate for symptoms of liver disease. Blood tests may be used, particularly liver function tests, and other blood tests may be used to investigate the presence of the Hepatitis viruses in the blood, and ultrasound used. If ascites is present, abdominal fluid may be tested for protein levels.[5]^{: 921, 926–927}

Pancreatic diseases that affect digestion refers to disorders affecting the exocrine pancreas, which is a part of the pancreas involved in digestion.

One of the most common conditions of the exocrine pancreas is acute pancreatitis, which in the majority of cases relates to gallstones that have impacted in the pancreatic part of the biliary tree, or due to acute or chronic hazardous alcohol use or as a side-effect of ERCP. Other forms of pancreatitis include chronic and hereditary forms. Chronic pancreatitis may predispose to pancreatic cancer and is strongly linked to alcohol use. Other rarer diseases affecting the pancreas may include pancreatic pseudocysts, exocrine pancreatic insufficiency, and pancreatic fistulas.[5]^{: 888–891}

Pancreatic disease may present with or without symptoms. When symptoms occur, such as in acute pancreatitis, a person may experience acute-onset, severe mid-abdominal pain, nausea and vomiting. In severe cases, pancreatitis may lead to rapid blood loss and systemic inflammatory response syndrome. When the pancreas is unable to secrete digestive enzymes, such as with a pancreatic cancer occluding the pancreatic duct, result in jaundice. Pancreatic disease might be investigated using abdominal x-rays, MRCP or ERCP, CT scans, and through blood tests such as measurement of the amylase and lipase enzymes.[5]^{: 888–894}

Diseases of the hepatobiliary system affect the biliary tract (also known as the biliary tree), which secretes bile in order to aid digestion of fats. Diseases of the gallbladder and bile ducts are commonly diet-related, and may include the formation of gallstones that impact in the gallbladder (cholecystolithiasis) or in the common bile duct (choledocholithiasis).[5]^{: 977–978}

Gallstones are a common cause of inflammation of the gallbladder, called cholecystitis. Inflammation of the biliary duct is called cholangitis, which may be associated with autoimmune disease, such as primary sclerosing cholangitis, or a result of bacterial infection, such as ascending cholangitis.[5]^{: 977–978, 963–968}

Disease of the biliary tree may cause pain in the upper right abdomen, particularly when pressed. Disease might be investigated using ultrasound or ERCP, and might be treated with drugs such as antibiotics or UDCA, or by the surgical removal of the gallbladder.[5]^{: 977–979}

The Wikipedia article "Gastrointestinal cancer" describes the specific malignant conditions of the gastrointestinal tract. In general, a significant factor in the etiology of gastrointestinal cancers appears to be excessive exposure of the digestive organs to bile acids.[12][13]