Hepatic flexure

By the end of the small intestine, deposition is almost complete and there is no need for intestinal secretions to aid assimilation. The principal role of the colon is to resorb water and reclaim sodium, which it does very efficiently. In fact, for every 2 L of water entering the colon, the residual water in the stools will be <200 mL. The environment becomes problematic for delivery past the hepatic flexure as the lack of water will restrict dispersion and dissolution. The flow of chyme from the ileum to the colon in healthy human beings is 1-2 L h 1. 

For most formulations, colonic absorption represents the only real opportunity to increase the interval between doses. Transit through the lower part of the gut is quoted at about 24h, but in reality only the ascending colonic environment has sufficient fluid to facilitate dissolution. In the cecum, the fermentation of soluble fiber produces fatty acids and gas [33].The gas rises into the transverse colon and can form temporary pockets, restricting access of water to the formulation. Consequently, distal release of drug is associated with poor spreading, reduced surface area, and restricted absorption. In the colon, water availability is also low past the hepatic flexure, as the ascending colon is extremely efficient at water absorption [34],... 

The presence of large volumes of gas appears to restrict the availability of water past the hepatic flexure, and the consequences of this must be carefully considered. 

In vitro cumulative percent drug release with rat caecal medium (2%, 21 hr study) is <20 %. In vivo scintigraphy study shows intact tablet in small intestine (2 hr), with commencement of disintegration of coat (4 hr), distribution of broken pieces of tablet in ascending colon, hepatic flexure, transverse colon, and splenic flexure (8 hr). 

Fig. 4.5.a Coronal reformatted image of the transverse colon. Yellow open triangle shows the virtual camera looking in the transverse colon near the hepatic flexure, b Corresponding 3D view shows pseudopolypoid lesions caused by the tagged residue (arrowheads)... 

Fig. 4.16.a Non-tagged fluid covering 25-50% of the colonic lumen at the hepatic flexure in supine position (white arrows). Tagged residue in the fluid (open black arrowhead), b In the prone position the fluid is redistributed to the anterior part of the hepatic flexure (white arrowheads) and the transverse colon (black arrowhead) enabling complete visualisation of the colonic wall. Tagged residue is visible (black arrow)... 

The cecum, hepatic flexure, transverse colon, splenic flexure, and sigmoid colon, are to be considered as areas of danger because of the convoluted and mobile nature. 

Complex or thickened folds are typically encountered at the splenic and hepatic flexures. Axial CT images might raise the possibility of intraluminal soft tissue masses or tumoral thickened folds. Endo-luminal views are frequently helpful in identifying... 

Fig. 8.29a,b. False positive diagnosis complex folds a axial image shows the splenic flexure, with a thickened nodular-like fold (arrow) b corresponding endoluminal 3D image clearly shows that the thickened nodular appearance is to be explained by the complexity of the folds at the splenic flexure. Lesson Complex or thickened folds are typically encountered at the splenic and hepatic flexures, and should be differentiated from sessile cancers or polyps. Endoluminal 3D images are extremely helpful for differential diagnosis. Compare with Fig. 8.18... 

Fig. 31.5a-d CTC showing sessile adenomatous polypoid lesion of hepatic flexure, a Axial 2D image obtained on prone position showing a 1.5-cm sessile, polypoid lesion of hepatic flexure, b Corresponding 3D image shows endoscopical appearance of the lesion, c Axial 2D image obtained after turning... 

Except for the duodenal bulb, vdiich is an intra-peritoneal segment, the duodenum is a retroperitoneal structure, partially covered with peritoneum over its anterior aspect, and located within the anterior pararenal space. At this location it bears a close relation with important contiguous viscera such as the pancreatic head, the hepatic flexure, the right kidney, and the gallbladder, as well as with major vascular structures [the inferior vena cava, (IVC), the abdominal aorta, and the superior mesenteric vessels] (Gray 1995). A variety of pathological processes in these structures may have a secondary effect on the duodenum. 

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