Gastrointestinal

Gastrointestinal diseases affect the gastrointestinal (GI) tract from the mouth to the anus. There are two types: functional and structural. Some examples include nausea/vomiting, food poisoning, lactose intolerance and diarrhea.

gastrointestinal

Structural gastrointestinal diseases are those where your bowel looks abnormal upon examination and also doesn't work properly. Sometimes, the structural abnormality needs to be removed surgically. Common examples of structural GI diseases include strictures, stenosis, hemorrhoids, diverticular disease, colon polyps, colon cancer and inflammatory bowel disease.

The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and other animals, including the esophagus, stomach, and intestines. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled at the anus as feces. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines.

The human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts.[3] The GI tract includes all structures between the mouth and the anus,[4] forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. The complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder).[5] The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment. The whole human GI tract is about nine metres (30 feet) long at autopsy. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis.[6][7]

The gastrointestinal tract contains the gut microbiota, with some 1,000 different strains of bacteria having diverse roles in maintenance of immune health and metabolism, and many other microorganisms.[8][9][10] Cells of the GI tract release hormones to help regulate the digestive process. These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.[11]

The upper gastrointestinal tract consists of the mouth, pharynx, esophagus, stomach, and duodenum.[13]The exact demarcation between the upper and lower tracts is the suspensory muscle of the duodenum. This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of either "upper" or "lower" origin. Upon dissection, the duodenum may appear to be a unified organ, but it is divided into four segments based upon function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): bulb, descending, horizontal, and ascending. The suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm.

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine.[15] In human anatomy, the intestine (bowel, or gut. Greek: éntera) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the stomach to the anus and as in other mammals, consists of two segments: the small intestine and the large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunum, and ileum while the large intestine is subdivided into the cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.[16][17]

The gastrointestinal tract has a form of general histology with some differences that reflect the specialization in functional anatomy.[22] The GI tract can be divided into four concentric layers in the following order:

The mucosa is the innermost layer of the gastrointestinal tract. The mucosa surrounds the lumen, or open space within the tube. This layer comes in direct contact with digested food (chyme). The mucosa is made up of:

The muscular layer consists of an inner circular layer and a longitudinal outer layer. The circular layer prevents food from traveling backward and the longitudinal layer shortens the tract. The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch.[23] Whilst the muscularis externa is similar throughout the entire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food. The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer, and outer longitudinal layer.

Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example, Clostridia, one of the most predominant bacterial groups in the GI tract, play an important role in influencing the dynamics of the gut's immune system.[36] It has been demonstrated that the intake of a high fiber diet could be responsible for the induction of T-regulatory cells (Tregs). This is due to the production of short-chain fatty acids during the fermentation of plant-derived nutrients such as butyrate and propionate. Basically, the butyrate induces the differentiation of Treg cells by enhancing histone H3 acetylation in the promoter and conserved non-coding sequence regions of the FOXP3 locus, thus regulating the T cells, resulting in the reduction of the inflammatory response and allergies.

Various pathogens, such as bacteria that cause foodborne illnesses, can induce gastroenteritis which results from inflammation of the stomach and small intestine. Antibiotics to treat such bacterial infections can decrease the microbiome diversity of the gastrointestinal tract, and further enable inflammatory mediators.[39] Gastroenteritis is the most common disease of the GI tract.

Inflammatory bowel disease is an inflammatory condition affecting the bowel walls, and includes the subtypes Crohn's disease and ulcerative colitis. While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine. Crohn's disease is widely regarded as an autoimmune disease. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such.

Functional gastrointestinal disorders the most common of which is irritable bowel syndrome. Functional constipation and chronic functional abdominal pain are other functional disorders of the intestine that have physiological causes but do not have identifiable structural, chemical, or infectious pathologies.

Gastrointestinal stromal tumours are the most common mesenchymal neoplasm of the gastrointestinal tract and are highly resistant to conventional chemotherapy and radiotherapy. Such tumours usually have activating mutations in either KIT (75-80%) or PDGFRA (5-10%), two closely related receptor tyrosine kinases. These mutations lead to ligand-independent activation and signal transduction mediated by constitutively activated KIT or PDGFRA. Targeting these activated proteins with imatinib mesylate, a small-molecule kinase inhibitor, has proven useful in the treatment of recurrent or metastatic gastrointestinal stromal tumours and is now being tested as an adjuvant or neoadjuvant. However, resistance to imatinib is a growing problem and other targeted therapeutics such as sunitinib are available. The important interplay between the molecular genetics of gastrontestinal stromal tumour and responses to targeted therapeutics serves as a model for the study of targeted therapies in other solid tumours.

The Gastrointestinal Medical Oncology department is a team of highly specialized medical oncologists, scientists, physician assistants and research nurses who treat gastrointestinal malignancies, including cancers of the liver, bile duct, gallbladder, pancreas, large and small bowel, stomach, esophagus and rare tumors.

Our goal is to deliver the highest quality patient care by providing the most advanced medical therapies and opportunities to participate in clinical trials, with the goal of improving survival and quality of life. Research scientists are working to find better therapies, as well as more accurate diagnosis and screening procedures to detect GI cancers in their earliest stages. Fellowship and residency programs are available to train future generations of gastrointestinal oncologists.

The Committee reviews and evaluates available data concerning the safety and effectiveness of marketed and investigational human drug products for use in the treatment of gastrointestinal diseases and makes appropriate recommendations to the Commissioner of Food and Drugs.

Gastrointestinal stromal tumors (GISTs) are uncommon cancers that start in special cells in the wall of the gastrointestinal (GI) tract, also known as the digestive tract. To understand GISTs, it helps to know something about the structure and function of the GI tract.

Morgan J, Raut CP, Duensing A, Keedy VL. Epidemiology, classification, clinical presentation, prognostic features, and diagnostic work-up of gastrointestinal stromal tumors (GIST). UpToDate. 2019. Accessed at -classification-clinical-presentation-prognostic-features-and-diagnostic-work-up-of-gastrointestinal-stromal-tumors-gist on October 14, 2019. 350c69d7ab