Gastrointestinal diseases (abbrev. GI diseases or GI illnesses) refer to diseases involving the gastrointestinal tract, namely the oesophagus, stomach, small intestine, large intestine and rectum, and the accessory organs of digestion, the liver, gallbladder, and pancreas. Oral disease The oral cavity is part of the gastrointestinal system and as such the presence of alterations in this district can be the first sign of both systemic and gastrointestinal diseases. By far the most common oral conditions are plaque-induced diseases (e.g., gingivitis, periodontitis, dental caries). Oral symptoms can be similar to lesions occurring elsewhere in the digestive tract, with a pattern of swelling, inflammation, ulcers, and fissures. If these signs are present, then patients are more likely to also have anal and esophageal lesions and experience other extra-intestinal disease manifestations. Some diseases which involve other parts of the GI tract can manifest in the mouth, alone or in combination, including: Gastroesophageal reflux disease can cause acid erosion of the teeth and halitosis. Gardner's syndrome can be associated with failure of tooth eruption, supernumerary teeth, and dentigerous cysts. Peutz–Jeghers syndrome can cause dark spots on the oral mucosa or on the lips or the skin around the mouth. Several GI diseases, especially those associated with malabsorption, can cause recurrent mouth ulcers, atrophic glossitis, and angular cheilitis (e.g., Crohn's disease is sometimes termed orofacial granulomatosis when it involves the mouth alone). Sideropenic dysphagia can cause glossitis, angular cheilitis. Oesophageal disease Oesophageal diseases include a spectrum of disorders affecting the oesophagus. The most common condition of the oesophagus in Western countries is gastroesophageal reflux disease, which in chronic forms is thought to result in changes to the epithelium of the oesophagus, known as Barrett's oesophagus. Acute disease might include infections such as oesophagitis, trauma caused by the ingestion of corrosive substances, or rupture of veins such as oesophageal varices, Boerhaave syndrome or Mallory-Weiss tears. Chronic diseases might include congenital diseases such as Zenker's diverticulum and esophageal webbing, and oesophageal motility disorders including the nutcracker oesophagus, achalasia, diffuse oesophageal spasm, and oesophageal stricture. Oesophageal disease may result in a sore throat, throwing up blood, difficulty swallowing or vomiting. Chronic or congenital diseases might be investigated using barium swallows, endoscopy and biopsy, whereas acute diseases such as reflux may be investigated and diagnosed based on symptoms and a medical history alone. Gastric disease Gastric diseases refer to diseases affecting the stomach. Inflammation of the stomach by infection