Small intestine segments

Location and extent Gastric stomach Similar flora present in duodenum and proximal jejunum Small intestine, segmental or global Backwards colonization of the stomach in severe forms... 

The site and mechanism of absorption of ingested americium are not known. Based on studies of plutonium, it is likely that americium absorption occurs, at least to some extent, in the small intestine. Studies of the absorption of plutonium in preparations of in situ isolated segments of small intestine of immature miniature swine indicate that absorption of actinides can occur along the entire small intestine, with the highest rates of absorption occurring in the duodenum (Sullivan and Gorham 1982). 

The surface area in the luminal side of the small intestine per unit length of the serosal (blood) side is enormous in the proximal jejunum, and steadily decreases (to about 20% of the starting value [62]) in the distal portions of the small intestine. The surface area is increased threefold [69] by ridges oriented circumferentially around the lumen. Similar folds are found in all segments of the GIT, except the mouth and esophagus [66]. Further 4—10-fold expansion [62,69] of the surface is produced by the villi structures, shown schematically in Fig. 2.4. The layer of epithelial cells lining the villi structures separate the lumen from the circulatory system. Epithelial cells are made in the crypt folds of the villi, and take about... 

The advantage of the mixing tank model approach is its relative simplicity, intuitive accessibility, and easy correlation with pharmacokinetic models. However, the physical basis for considering a segment of the small intestine as one or more serial mixing tanks is limited, although such an assumption has been commonly and successfully utilized in the physical and biological sciences. 

Bile is produced continuously by the liver bile salts are secreted by the hepatocytes and the water, sodium bicarbonate, and other inorganic salts are added by the cells of the bile ducts within the liver. The bile is then transported by way of the common bile duct to the duodenum. Bile facilitates fat digestion and absorption throughout the length of the small intestine. In the terminal region of the ileum, the final segment of the small intestine, the bile salts are actively reabsorbed into the blood, returned to the liver by way of the hepatic portal system, and resecreted into the bile. This recycling of the bile salts from the small intestine back to the liver is referred to as enterohepatic circulation. 

The small intestine is the longest (>6 m) and most convoluted organ in the digestive system. It is divided into three segments ... 

Segmentation contractions occur as a result of the basic electrical rhythm (BER) of pacemaker cells in the small intestine. This form of muscular activity is slight or absent between meals. The motility of the small intestine may be enhanced during a meal by ... 

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. 

Fig. 7.3. The total Loc-I-Gut concept. Left a perfusion system of the duodenal segment. Center a tube system with double balloons which allow a segmental single-pass perfusion of jejunum. Right a perfusion system of the small intestinal stomi.

Bayliss and Starling [ 104] described the peristaltic reflex of small intestine in 1899. This enterically controlled reflex elicits a contraction oral to and a relaxation distal to a segmental distension, resulting in the movement of contents in the aboral direction [104], The peristaltic reflex is funda-... 

A small bowel transit study can be used to evaluate intestinal propulsion and clearance, and the presence of Enterobacteriacea (Gram-negative bacilli) in the small bowel indicates delayed transit [111]. The wide normal variability, however, makes transit tests rather insensitive, and thus less useful clinically [126, 127], It is also a problem that accelerated and delayed transit may coexist in neuropathies and confuse the interpretation. Finally, as nutrients are mostly absorbed in the proximal small bowel, and the rate and pattern of transit vary along the intestine, segmental failure of transit is easily missed by global... 

Search for fistula, large or multiple small intestinal diverticula, and an enlarged surgical blind loop (X-ray) or confined segment of intestine... 

F24. Frazer, A. C., French, J. M., and Thompson, M. D., Radiographic studies showing induction of a segmentation pattern in the small intestine in normal human subjects. Brit. J. Radiol. 22, 123 (1949). 

Figure 18 Segment of the human small intestine with folds of mucous membrane (prepared by plastination). The total length of the human small intestine is estimated to be about 3.5-3.8m. Source From Ref. 90.

Cong D, Fong AK, Lee R and Pang KS (2001) Absorption of Benzoic Acid in Segmental Regions of the Vascularly Perfused Rat Small Intestine Preparation. Drug Metab Dispos 29 pp 1539-1547. 

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