The large intestine (or "large bowel") is the second-to-last part of the digestive system — the final stage of the alimentary canal is the anus — in vertebrate animals. Its function is to absorb water from the remaining indigestible food matter, and then to pass useless waste material from the body. This article is primarily about the human gut, though the information about its processes are directly applicable to most mammals.
The large intestine consists of the cecum and colon. It starts in the right iliac region of the pelvis, just at or below the right waist, where it is joined to the bottom end of the small intestine. From here it continues up the abdomen, then across the width of the abdominal cavity, and then it turns down, continuing to its endpoint at the anus.
The large intestine is about 1.5 metres (4.9 ft) long, which is about one-fifth of the whole length of the intestinal canal.
In Terminologia Anatomica the large intestine includes the cecum, colon, rectum, and anal canal. However, some sources exclude the anal canal.
Function and relation to other organs
The large intestine takes about 32 hours to finish up the remaining processes of the digestive system. Food is no longer broken down at this stage of digestion. The large intestine absorbs water and electrolytes from the approximate 1.5L of chyme passing through the ileocecal valve daily. The colon absorbs vitamins which are created by the colonic bacteria - such as Vitamin K (especially important as the daily ingestion of Vit. K is not normally enough to maintain adequate blood coagulation), Vitamin B12, thiamine and riboflavin. It also compacts feces, and stores fecal matter in the rectum until it can be discharged via the anus in defecation.
The large intestine differs in physical form from the small intestine in being much wider and in showing the longitudinal layer of the muscularis have been reduced to 3 strap-like structures known as the taeniae coli. The wall of the large intestine is lined with simple columnar epithelium. Instead of having the invaginations of the small intestine (villi), the large intestine has invaginations (the intestinal glands). While both the small intestine and the large intestine have goblet cells, they are abundant in the large intestine.
The vermiform appendix is attached to its posteromedial surface of the large intestine. It contains masses of lymphoid tissue. It is a part of mucosa-associated lymphoid tissue, which gives the appendix an important role in immunity. Appendicitis is the result of a blockage that traps infectious material in the lumen. The appendix can be removed with no damage or consequence to the patient. The large intestine extends from the ileocecal junction to the anus and is about 1.5m long. On the surface, bands of longitudinal muscle fibers called taeniae coli, each about 5 mm wide, can be identified. There are three bands, and they start at the base of the appendix and extend from the cecum to the rectum. Along the sides of the taeniae, tags of peritoneum filled with fat, called epiploic appendages (or appendices epiploicae) are found. The sacculations, called haustra, are characteristic features of the large intestine, and distinguish it from the small intestine. It is also found in the digestive system.
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