Gastrointestinal tract intestine

Only a small (ca 3%) fraction of ingested or inhaled manganese is absorbed, which occurs primarily by the intestines (209). Once absorbed, manganese is regulated by the Hver, where it is excreted into the bile and passes back into the intestine, where some reabsorption may occur (210). Manganese is elirninated almost exclusively (>95%) by the bile in the gastrointestinal tract. 

The largest use of endoscopic techniques is in the examination of the gastrointestinal tract. Upper intestinal endoscopy is the examination of the esophagus, stomach, and proximal duodenum. Colonoscopy is the examination of the colon, large intestine, and in some cases the distal parts of the small intestine. Cholangiopancreatography is the examination of the biUary tree and pancreas. 

Toxicity. The toxicity of barium compounds depends on solubility (47—49). The free ion is readily absorbed from the lung and gastrointestinal tract. The mammalian intestinal mucosa is highly permeable to Ba " ions and is involved in the rapid flow of soluble barium salts into the blood. Barium is also deposited in the muscles where it remains for the first 30 h and then is slowly removed from the site (50). Very Httle is retained by the fiver, kidneys, or spleen and practically none by the brain, heart, and hair. 

Soluble Compounds. The mechanism of barium toxicity is related to its ability to substitute for calcium in muscle contraction. Toxicity results from stimulation of smooth muscles of the gastrointestinal tract, the cardiac muscle, and the voluntary muscles, resulting in paralysis (47). Skeletal, arterial, intestinal, and bronchial muscle all seem to be affected by barium. 

Pituitary Adenylyl Cyclase-activating Polypeptide (PACAP) is a 38-amino acid peptide (PACAP-38), which is widely expressed in the central nervous system. PACAP is most abundant in the hypothalamus. It is also found in the gastrointestinal tract, the adrenal gland and in testis. Its central nervous system functions are ill-defined. In the periphery, PACAP has been shown to stimulate catecholamine secretion from the adrenal medulla and to regulate secretion from the pancreas. Three G-protein coupled receptors have been shown to respond to PACAP, PAQ (PACAP type I) specifically binds PACAP, VPACi and VPAC2 also bind vasoactive intestinal peptide (VDP). Activation of PACAP receptors results in a Gs-mediated activation of adenylyl cyclase. 

Gastrointestinal tract—nausea, vomiting, diarrhea, constipation, epigastric pain, indigestion, abdominal distress or discomfort, intestinal ulceration, stomatitis, jaundice, bloating, anorexia, and dry mouth... 

Gastrointestinal tract-decrease in secretions of the stomach, decrease in gastric and intestinal movement (motility)... 

Delivery of peptides and proteins via the gastrointestinal tract has not been successful because of poor penetration through the intestinal epithelium and high levels of proteolytic activity in the gastrointestinal tract. Liposomal encapsulation of proteins and peptides will not improve the efficiency and capacity of this absorption pathway considerably (e.g., Ryman et al., 1982 Machy and Leserman, 1987 Weiner and Chia-Ming Chiang, 1988). These difficulties in delivery via the oral route caused the parenteral route to remain the preferred route for the administration of therapeutic peptides... 

Parenteral Fluids. During the past ten years interest has been renewed in the total alimentation of the infant by vein (2). The motivation for this is the fact that neonates may suffer from some congenital malformation of the intestinal tract which would require surgical resection. If this is done, then one needs some outside way for alimentation, bypassing the intestine, until the intestine is able to heal and recover its normal function. This may take many weeks. A second source of motivation is the small premature infant weighing less than a kilogram, whose immature central nervous system and gastrointestinal tract make it difficult to establish nutrition by oral intake soon after birth. These also require total intravenous nutrition for a substantial period of time. 

Nystatin has a specific action on C. albicans and is of no value in the treatment of any other type of infection. It is poorly absorbed from the gastrointestinal tract even after very large doses, the blood level is insignificant. It is administered orally in the treatment of oral thrush and intestinal candidiasis infections. 

Myo-inositol is one of the most biologically active forms of inositol. It exists in several isomeric forms, the most common being the constituent of phospholipids in biological cell membranes. It also occurs as free inositol and as inositol hexaphosphate (IP6) also known as phytate which is a major source from food. Rice bran is one of the richest sources of IP6 as well as free inositol. Inositol is considered to belong to the B-complex vitamins. It is released in the gastrointestinal tract of humans and animals by the dephosphorylation of IP6 (phytate) by the intestinal enzyme phytase. Phytase also releases intermediate products as inositol triphosphate and inositol pentaphosphate. Inositol triphosphate in cellular membrane functions as an important intra- and intercellular messenger, that merits its value as a nutritional therapy for cancer. 

It has recently been shown (14) that nitrate from food can be detected in the feces of germfree animals but not in the feces of conventional animals. This result and the results of Witter et al. (18-20) suggest that nitrate is available in the lower gastrointestinal tract and is metabolized by the microbial flora. The intestine may thus be a site for the endogenous formation of N-nitroso compounds. 

It is conceivable that nltrosamlnes can be synthesized In the Intestine, since the precursors are present. While the conditions for aqueous nltrosatlon reactions are not optimum at pH values encountered In the lower gastrointestinal tract, several studies have shown that these reactions can be catalyzed (39, 40, 41). It has been suggested that the Intestine might be a site for the formation of nltrosamlnes by bacterial action (42). Sander (43) has demonstrated the formation of nltrosamlnes by bacterial action from precursor amines and nitrate at neutral pH and Klubes and coworkers have reported the formation of NDMA. upon Incubation of l C-dlmethylamlne and sodium nitrite with rat fecal contents (44, 45). 

Different factors inclnding nntrients, bile salts, pH, and microflora present in the gastrointestinal tract dnring the digestion process can affect the bioaccessibility of a compound (Table 3.2.1). The compoimd of interest is generally consiuned together with other nutrients present in the meal and, once the compound and these nutrients are released from the food matrix during the same period, they may interact in the intestinal liunen. 

Milieu conditions in gastrointestinal tract can influence the pectin structure and properties. Under the acid conditions of the stomach (pH 2-4) extraction of pectin from plant cell walls and hydrolysis of side chains can occur. In small intestine (pH 5-6) -elimination of main chains or de-esterification seems to be possible. In caecum and colon (pH 6-8) a strong fermentation of pectin takes place causing depolymerization to oligomers and leading to formation of short chain fatty acids and gases. The presence of OligoGalA is not yet clarified. 

The liver is a wedge-shaped organ of some 1.5 kg in adult humans, which, in terms of blood circulation, is interposed between the gastrointestinal tract and the rest of the body. The blood supply to the liver is from the hepatic portal vein (80%) and the hepatic artery (20%), the former bringing a rich supply of nutrients direct from the intestinal tract and the latter supplying the liver with oxygen. Blood drains from the liver by the hepatic vein. The position of the liver enables it to act as a processor of the absorbed nutrients, and to control their storage... 

During normal processes, approximately 9 liters of fluid traverse the gastrointestinal tract daily. Of this amount, 2 liters represent gastric juice, 1 liter is saliva, 1 liter is bile, 2 liters are pancreatic juice, 1 liter is intestinal secretions, and 2 liters are ingested. Of these 9 L of fluid presented to the intestine, only about 150 to 200 mL remain in the stool after reabsorptive processes occur. 

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