Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones.
In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication, a form of mechanical digestion, and the wetting contact of saliva. Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which is waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes.
Lower gastrointestinal bleeding, commonly abbreviated LGIB, refers to any form of bleeding in the lower gastrointestinal tract. LGIB is a common ailment seen at emergency departments. It presents less commonly than upper gastrointestinal bleeding (UGIB). It is estimated that UGIB accounts for 100–200 per 100,000 cases versus 20–27 per 100,000 cases for LGIB. Approximately 85% of lower gastrointestinal bleeding involves the colon, 10% are from bleeds that are actually upper gastrointestinal bleeds, and 3–5% involve the small intestines. The mortality rate for LGIB is between 2–4%.
A lower Gastrointestinal Bleed is referred as any bleed that occurs distal to the ligament of Treitz and superior to the anus. This includes the last 1/4 of the duodenum and the entire area of the jejunum, ileum, colon, rectum, and anus.
Colorectal surgery is a field in medicine, dealing with disorders of the rectum, anus, and colon. The field is also known as proctology, but the latter term is now used infrequently within medicine, and is most often employed to identify practices relating to the anus and rectum in particular. The word proctology is derived from the Greek words πρωκτός ("Proktos"), meaning anus or hindparts, and λόγος ("Logos") meaning science or study.
Physicians specializing in this field of medicine are called colorectal surgeons or proctologists. In the United States, to become colorectal surgeons, these surgical doctors have to complete a general surgery residency, as well as a colorectal surgery fellowship, upon which they are eligible to be certified in their field of expertise by the American Board of Colon and Rectal Surgery or the American Osteopathic Board of Proctology. In other countries, certification to practice proctology is given to surgeons at the end of a 2-3 year subspecialty residency by the country's board of surgery.