Digestive system large intestine

Obviously, satisfactory colonic absorption of the drug to be delivered is a sine qua non for the successful development of a colonic drug delivery system. However, situations exist when even reduced absorption from the large intestine (compared with the small intestine) would still justify colonic delivery, for instance in the case of a peptide drug that would otherwise be efficiently digested in the small intestine. 

Rat experiments have demonstrated that the absorbed iron passes from intestinal cells to portal plasma largely in a low molecular weight (LMW) form (12). An additional factor would be the age of the infant in which the role of gastric acidity and proteolytic enzyme would have to be considered. As the young infant ages the digestive system develops its ability to function as a complete organ. In neonates, however, iron absorption appears to be less dependent on intermediary iron metabolism and more on the iron supplied by milk. 

The digestive system consists of the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus together with the liver and pancreas. 

The small intestine is the most important part of the digestive system for digestion because it produces many enzymes and is highly adapted for absorption of nutrients. It has a large overall surface area because of its length and because its inner lining is folded into villi. 

These metabolites were generated during digestion and intestinal absorption as a result of phase II enzymes and were converted into glucuronidated and sulfated metabolites as well as methylated metabolites. The procyanidins, which were not absorbed in the small intestine, passed into the large intestine where they were degraded by the colonic microflora into phenolic acids, which could be absorbed into the circulatory system and subjected to phase II metabolism prior to excretion. Serra et al. [34] used a colonic fermentation model with rat colonic microflora and reported that the phen-ylacetic acid and its hydroxylated forms were the main fermentation products, and hydroxy-y-valerolactone was specifically from procyanidin compounds. 

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