Gastritis: Inflammation of the GASTRIC MUCOSA, a lesion observed in a number of unrelated disorders.Gastritis, Atrophic: GASTRITIS with atrophy of the GASTRIC MUCOSA, the GASTRIC PARIETAL CELLS, and the mucosal glands leading to ACHLORHYDRIA. Atrophic gastritis usually progresses from chronic gastritis.Helicobacter pylori: A spiral bacterium active as a human gastric pathogen. It is a gram-negative, urease-positive, curved or slightly spiral organism initially isolated in 1982 from patients with lesions of gastritis or peptic ulcers in Western Australia. Helicobacter pylori was originally classified in the genus CAMPYLOBACTER, but RNA sequencing, cellular fatty acid profiles, growth patterns, and other taxonomic characteristics indicate that the micro-organism should be included in the genus HELICOBACTER. It has been officially transferred to Helicobacter gen. nov. (see Int J Syst Bacteriol 1989 Oct;39(4):297-405).Gastric Mucosa: Lining of the STOMACH, consisting of an inner EPITHELIUM, a middle LAMINA PROPRIA, and an outer MUSCULARIS MUCOSAE. The surface cells produce MUCUS that protects the stomach from attack by digestive acid and enzymes. When the epithelium invaginates into the LAMINA PROPRIA at various region of the stomach (CARDIA; GASTRIC FUNDUS; and PYLORUS), different tubular gastric glands are formed. These glands consist of cells that secrete mucus, enzymes, HYDROCHLORIC ACID, or hormones.Helicobacter Infections: Infections with organisms of the genus HELICOBACTER, particularly, in humans, HELICOBACTER PYLORI. The clinical manifestations are focused in the stomach, usually the gastric mucosa and antrum, and the upper duodenum. This infection plays a major role in the pathogenesis of type B gastritis and peptic ulcer disease.Pyloric Antrum: The region between the sharp indentation at the lower third of the STOMACH (incisura angularis) and the junction of the PYLORUS with the DUODENUM. Pyloric antral glands contain mucus-secreting cells and gastrin-secreting endocrine cells (G CELLS).Gastritis, Hypertrophic: GASTRITIS with HYPERTROPHY of the GASTRIC MUCOSA. It is characterized by giant gastric folds, diminished acid secretion, excessive MUCUS secretion, and HYPOPROTEINEMIA. Symptoms include VOMITING; DIARRHEA; and WEIGHT LOSS.Metaplasia: A condition in which there is a change of one adult cell type to another similar adult cell type.Stomach: An organ of digestion situated in the left upper quadrant of the abdomen between the termination of the ESOPHAGUS and the beginning of the DUODENUM.Gastroscopy: Endoscopic examination, therapy or surgery of the interior of the stomach.Pepsinogen A: This is one of 2 related pepsinogen systems in humans and is also known as pepsinogen. (The other is PEPSINOGEN C.) This includes isozymogens Pg1-Pg5 (pepsinogens 1-5, group I or products of PGA1-PGA5 genes). This is the main pepsinogen found in urine.Stomach Neoplasms: Tumors or cancer of the STOMACH.Achlorhydria: A lack of HYDROCHLORIC ACID in GASTRIC JUICE despite stimulation of gastric secretion.Bile Reflux: Retrograde bile flow. Reflux of bile can be from the duodenum to the stomach (DUODENOGASTRIC REFLUX); to the esophagus (GASTROESOPHAGEAL REFLUX); or to the PANCREAS.Stomach Ulcer: Ulceration of the GASTRIC MUCOSA due to contact with GASTRIC JUICE. It is often associated with HELICOBACTER PYLORI infection or consumption of nonsteroidal anti-inflammatory drugs (NSAIDS).Gastrins: A family of gastrointestinal peptide hormones that excite the secretion of GASTRIC JUICE. They may also occur in the central nervous system where they are presumed to be neurotransmitters.Peptic Ulcer: Ulcer that occurs in the regions of the GASTROINTESTINAL TRACT which come into contact with GASTRIC JUICE containing PEPSIN and GASTRIC ACID. It occurs when there are defects in the MUCOSA barrier. The common forms of peptic ulcers are associated with HELICOBACTER PYLORI and the consumption of nonsteroidal anti-inflammatory drugs (NSAIDS).Pepsinogen C: This is one of the 2 related pepsinogen systems in humans. It is found in prostate and seminal fluid whereas PEPSINOGEN A is not.Stomach Diseases: Pathological processes involving the STOMACH.Duodenal Ulcer: A PEPTIC ULCER located in the DUODENUM.Helicobacter felis: A species of HELICOBACTER that colonizes in the STOMACH of laboratory MICE; CATS; and DOGS. It is associated with lymphoid follicular hyperplasia and mild GASTRITIS in CATS.Helicobacter heilmannii: A species of gram-negative, spiral-shaped bacteria found in the gastric mucosa that is associated with chronic antral gastritis. This bacterium was first discovered in samples removed at endoscopy from patients investigated for HELICOBACTER PYLORI colonization.Parietal Cells, Gastric: Rounded or pyramidal cells of the GASTRIC GLANDS. They secrete HYDROCHLORIC ACID and produce gastric intrinsic factor, a glycoprotein that binds VITAMIN B12.Chronic Disease: Diseases which have one or more of the following characteristics: they are permanent, leave residual disability, are caused by nonreversible pathological alteration, require special training of the patient for rehabilitation, or may be expected to require a long period of supervision, observation, or care. (Dictionary of Health Services Management, 2d ed)Duodenitis: Inflammation of the DUODENUM section of the small intestine (INTESTINE, SMALL). Erosive duodenitis may cause bleeding in the UPPER GI TRACT and PEPTIC ULCER.Anemia, Pernicious: A megaloblastic anemia occurring in children but more commonly in later life, characterized by histamine-fast achlorhydria, in which the laboratory and clinical manifestations are based on malabsorption of vitamin B 12 due to a failure of the gastric mucosa to secrete adequate and potent intrinsic factor. (Dorland, 27th ed)Dyspepsia: Impaired digestion, especially after eating.Helicobacter: A genus of gram-negative, spiral-shaped bacteria that has been isolated from the intestinal tract of mammals, including humans. It has been associated with PEPTIC ULCER.Biopsy: Removal and pathologic examination of specimens in the form of small pieces of tissue from the living body.Urease: An enzyme that catalyzes the conversion of urea and water to carbon dioxide and ammonia. EC 3.5.1.5.Pepsinogens: Proenzymes secreted by chief cells, mucous neck cells, and pyloric gland cells, which are converted into pepsin in the presence of gastric acid or pepsin itself. (Dorland, 28th ed) In humans there are 2 related pepsinogen systems: PEPSINOGEN A (formerly pepsinogen I or pepsinogen) and PEPSINOGEN C (formerly pepsinogen II or progastricsin). Pepsinogen B is the name of a pepsinogen from pigs.Postgastrectomy Syndromes: Sequelae of gastrectomy from the second week after operation on. Include recurrent or anastomotic ulcer, postprandial syndromes (DUMPING SYNDROME and late postprandial hypoglycemia), disordered bowel action, and nutritional deficiencies.Gastric Juice: The liquid secretion of the stomach mucosa consisting of hydrochloric acid (GASTRIC ACID); PEPSINOGENS; INTRINSIC FACTOR; GASTRIN; MUCUS; and the bicarbonate ion (BICARBONATES). (From Best & Taylor's Physiological Basis of Medical Practice, 12th ed, p651)Precancerous Conditions: Pathological processes that tend eventually to become malignant. (From Dorland, 27th ed)Endoscopy, Gastrointestinal: Endoscopic examination, therapy or surgery of the gastrointestinal tract.Campylobacter: A genus of bacteria found in the reproductive organs, intestinal tract, and oral cavity of animals and man. Some species are pathogenic.Atrophy: Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes.Acinonyx: A genus of long-legged, swift-moving felines (FELIDAE) from Africa (and formerly Asia) about the size of a small leopard.Endoscopy: Procedures of applying ENDOSCOPES for disease diagnosis and treatment. Endoscopy involves passing an optical instrument through a small incision in the skin i.e., percutaneous; or through a natural orifice and along natural body pathways such as the digestive tract; and/or through an incision in the wall of a tubular structure or organ, i.e. transluminal, to examine or perform surgery on the interior parts of the body.Anti-Ulcer Agents: Various agents with different action mechanisms used to treat or ameliorate PEPTIC ULCER or irritation of the gastrointestinal tract. This has included ANTIBIOTICS to treat HELICOBACTER INFECTIONS; HISTAMINE H2 ANTAGONISTS to reduce GASTRIC ACID secretion; and ANTACIDS for symptomatic relief.Antigens, Bacterial: Substances elaborated by bacteria that have antigenic activity.Gastric Acid: Hydrochloric acid present in GASTRIC JUICE.H(+)-K(+)-Exchanging ATPaseAmoxicillin: A broad-spectrum semisynthetic antibiotic similar to AMPICILLIN except that its resistance to gastric acid permits higher serum levels with oral administration.Autoimmune Diseases: Disorders that are characterized by the production of antibodies that react with host tissues or immune effector cells that are autoreactive to endogenous peptides.Omeprazole: A 4-methoxy-3,5-dimethylpyridyl, 5-methoxybenzimidazole derivative of timoprazole that is used in the therapy of STOMACH ULCERS and ZOLLINGER-ELLISON SYNDROME. The drug inhibits an H(+)-K(+)-EXCHANGING ATPASE which is found in GASTRIC PARIETAL CELLS.Duodenogastric Reflux: Retrograde flow of duodenal contents (BILE ACIDS; PANCREATIC JUICE) into the STOMACH.Gastric Fundus: The superior portion of the body of the stomach above the level of the cardiac notch.Antibodies, Bacterial: Immunoglobulins produced in a response to BACTERIAL ANTIGENS.Endoscopy, Digestive System: Endoscopic examination, therapy or surgery of the digestive tract.Gastroenterostomy: A variety of surgical reconstructive procedures devised to restore gastrointestinal continuity, The two major classes of reconstruction are the Billroth I (gastroduodenostomy) and Billroth II (gastrojejunostomy) procedures.Intrinsic Factor: A glycoprotein secreted by the cells of the GASTRIC GLANDS that is required for the absorption of VITAMIN B 12 (cyanocobalamin). Deficiency of intrinsic factor leads to VITAMIN B 12 DEFICIENCY and ANEMIA, PERNICIOUS.Gastric Acidity Determination: Gastric analysis for determination of free acid or total acid.Bismuth: A metallic element that has the atomic symbol Bi, atomic number 83 and atomic weight 208.98.Bacterial Proteins: Proteins found in any species of bacterium.Thymectomy: Surgical removal of the thymus gland. (Dorland, 28th ed)Campylobacter Infections: Infections with bacteria of the genus CAMPYLOBACTER.Esophagitis: INFLAMMATION, acute or chronic, of the ESOPHAGUS caused by BACTERIA, chemicals, or TRAUMA.Antacids: Substances that counteract or neutralize acidity of the GASTROINTESTINAL TRACT.Lymphocytosis: Excess of normal lymphocytes in the blood or in any effusion.Gastrointestinal Diseases: Diseases in any segment of the GASTROINTESTINAL TRACT from ESOPHAGUS to RECTUM.Gastroesophageal Reflux: Retrograde flow of gastric juice (GASTRIC ACID) and/or duodenal contents (BILE ACIDS; PANCREATIC JUICE) into the distal ESOPHAGUS, commonly due to incompetence of the LOWER ESOPHAGEAL SPHINCTER.Gastrin-Secreting Cells: Endocrine cells which secrete GASTRIN, a peptide that induces GASTRIC ACID secretion. They are found predominantly in the GASTRIC GLANDS of PYLORIC ANTRUM in the STOMACH, but can also be found in the DUODENUM, nervous and other tissues.