The large intestine

No information is available at present on the effects of the many other secondary bile acids present in feces in small concentrations on water and electrolyte movement in the colon. In addition, no information is available on the role of bile acids in constipation, irritable bowel syndrome, nonspecific diarrhea, antibiotic diarrhea, or the diarrhea of the germ-free animal. Of interest is the response of the diarrhea of the germ-free animal to an anion exchange resin similar to cholestyramine (112). Studies are needed to define the structure-activity relationships for bile acids and the induction of water and sodium secretion by the colon. In addition, information is needed on the composition, concentration, and physical state of bile acids in colonic contents and feces in health and disease. 

Van den Oord, doctoral thesis. University of Utrecht, Netherlands, Schotanus Jens, Utrecht (1965). 

Ekwall, T. Rosendahl, and N. Ldfman, Acta Chem. Scand. 11, 590 (1957). 

Edsall and J. Wyman, Biophysical Chemistry, Vol. I, p. 466, Academic Press, New York (1958). 

Senior, T. B. Van Itallie, and N. J. Greenberger, eds., Medium Chain Triglycerides, University of Pennsylvania Press, Philadelphia (1968). 

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Intestinal flora is a general term for the bacteria yeast and fungi that live in the large intestine... 

Balantidiasis (balantidiosis, balantidial dysentery), an intestinal disease seen almost worldwide, is caused by the large ciUated protozoan, balantidium coll The organism is usually found in the lumen of the large intestine of humans and animals. Cysts formed in the lumen of the colon or in freshly evacuated feces of humans or domesticated and wild animals, can colonize the colon and terminal ileum of new hosts by the latter s ingestion of contaminated food or water. The hog has been found to be the most heavily parasitized host. Its association with the rat may be a means for maintaining a reservoir infection in the two animals. 

E. histolytica colonization of the large intestine is eradicated using a luminal agent such as diloxanid furoate or paromomycin. Invasive amoebiasis (colitis,... 

Entamoeba histolytica is an anaerobic rhizopod that occurs in tropical and subtropical areas. It can cause intestinal and extraintestinal manifestations. It is transmitted orally by ingestion of cysts that develop into trophozoites in the large intestine. Amebic trophozoites release several cytolytic factors, e.g. amoe-bapore, which enable the parasite to invade tissue. In intestinal amoebiasis, E. histolyticatrophozoites invade the intestinal mucosa, causing a form of ulcerative colitis with bloody and mucous diarrhoea. Extraintestinal manifestation of amebiasis results in abscess formation, usually in the liver but sometimes in the brain. 

Di-D-fructose dianhydrides have been claimed to promote the growth of bifidobacteria in vitro.134 Bifidobacterium spp. are found in the large intestines of most vertebrates.135 The benefits attributed to the presence of a healthy population of bifidobacteria in the gut include inhibition of carcinogenesis,136 suppression of putrefactive substances,137 lowering of blood pressure and blood... 

Irrespective of the physical form of the carotenoid in the plant tissue it needs to be dissolved directly into the bulk lipid phase (emulsion) and then into the mixed micelles formed from the emulsion droplets by the action of lipases and bile. Alternatively it can dissolve directly into the mixed micelles. The micelles then diffuse through the unstirred water layer covering the brush border of the enterocytes and dissociate, and the components are then absorbed. Although lipid absorption at this point is essentially complete, bile salts and sterols (cholesterol) may not be fully absorbed and are not wholly recovered more distally, some being lost into the large intestine. It is not known whether carotenoids incorporated into mixed micelles are fully or only partially absorbed. 

To date, there is very little known about if and how phytochemicals modulate the metabolism of GIT tissues other than the liver. Of particular interest are the xenobiotic metabolizing enzymes of the GIT, which are involved with transformation of drugs and toxins. Whereas the metabolic activities of the resident microflora dominate in the large intestine, mucosal enzyme activities are more important in the small intestine where bacterial densities are lower and the villi and microvilli increase the area of exposure. 

Stimulation of 5-HT3 receptors triggers hypersensitivity and hyperactivity of the large intestine. Alosetron (Lotronex) is a selective 5-HT3 antagonist that blocks these receptors and is used to treat women with severe diarrhea-predominant IBS. Eligible patients should have frequent and severe abdominal pain, frequent bowel urgency or incontinence, and restricted daily activities. Alosetron has been shown to improve overall symptoms and quality of life. Alosetron can cause constipation in some patients. 

The large intestine consists of the cecum the ascending, transverse, descending, and sigmoid colon segments and the... 

Four major tissue layers, from the lumen outward, form the large intestine the mucosa, submucosa, muscularis externa, and serosa (Fig. 88-2). Complete replacement of surface epithelial cells occurs approximately weekly, with the total number of epithelial cells remaining constant in normal colonic tissue. As patients age, abnormal cells accumulate on the surface epithelium and protrude into the stream of fecal matter their contact with fecal mutagens can lead to further cell mutations and eventual adenoma formation.4... 

Familial adenomatous polyposis An inherited condition in which numerous polyps form, mainly in the epithelium of the large intestine. While these polyps start out benign, malignant transformation into colon cancer occurs 100% of the time when not treated. 

In humans, the large intestine usually receives about 500 mL of fluid-like food material (chyme) per day. As... 

Fig. 6 (A) Scanning electron micrograph of the luminal surface of the large intestine (transverse colon magnification x 60). (From Ref. 9.) (B) Schematic diagram showing a longitudinal cross section of the large intestine. (C) Enlargement of cross section shown in B. (A and B modified from Ref. 10.)...

Structurally, the large intestine is similar to the small intestine, although the luminal surface epithelium of the former lacks villi. The muscularis mucosa, as in the small intestine, consists of inner circular and outer longitudinal layers. Figure 6 illustrates a photomicrograph and diagrammatic sketches of this region. 

Hydrogen sulfide is produced in the large intestine of mammals by metabolism of sulfhydryl proteins by anaerobic bacteria, and may compose 0-10% of intestinal gases (Beauchamp et al. 1984 EPA 1978). It is produced in the human mouth by microbial petrification (Rosenberg et al. 1991). 

The large intestine typically receives 500 to 1500 ml of chyme per day from the small intestine. As discussed, most digestion and absorption have... 

The colon s absorption of most of the water and salt from the chyme results in this "drying" or concentrating process. As a result, only about 100 ml of water is lost through this route daily. The remaining contents, now referred to as feces, are "stored" in the large intestine until it can be eliminated by way of defecation. 

The longitudinal layer of smooth muscle in the small intestine is continuous. In the large intestine, this layer of muscle is concentrated into three flat bands referred to as taniae coli. Furthermore, the large intestine appears to be subdivided into a chain of pouches or sacs referred to as haustra. The haustra are formed because the bands of taniae coli are shorter than the underlying circular layer of smooth muscle and cause the colon to bunch up, forming the haustra. 

In contrast to segmentation contractions in the small intestine (9 to 12 per minute), haustral contractions occur much less frequently (up to 30 min between contractions). These very slow movements allow for the growth of bacteria in the large intestine. Normally, the bacterial flora in this region is harmless. In fact, some of the bacteria produce absorbable vitamins, especially vitamin K. 

A second form of motility in the large intestine is mass movement. Three or four times per day, typically after a meal, a strong propulsive contraction occurs that moves a substantial bolus of chyme forward toward the distal portion of the colon. Mass movements may result in the sudden distension of the rectum that elicits the defecation reflex. 

Secretion of the large intestine. The large intestine produces an alkaline mucus secretion, the function of which is to protect the mucosa from mechanical or chemical injury. Mucus provides lubrication to facilitate the movement of the contents of the lumen. Bicarbonate ion neutralizes the irritating acids produced by local bacterial fermentation colonic secretion increases in... 

Hall, GA., Rutter, J.M. and Beer, R.J. (1976) A comparative study of the histopathology of the large intestine of conventionally reared, specific pathogen free and gnotobiotic pigs infected with Trichuris suis. Journal of Comparative Pathology 86, 285—292. 

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