Colon transverse

Fig. 13.2. Pseudomembranous colitis affecting the right colon. Transverse view on B-mode imaging shows the accordion sign related to oedema of the haustral folds...

A serious complication of UC is toxic megacolon, defined as dilation of the transverse colon of greater than 6 cm. Patients... 

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

Colonoscopy revealed multiple polyps in his transverse colon. 

LIVER GALLBLADDER I transverse colon ascending colon... 

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.)...

Fig. 23.4. Distribution of resin labeled with 111 In after four successive daily (morning) administrations among a cohort of normal volunteers and patients with active colitis. AC, ascending colon DC, distal colon RS, rectosigmoid colon TC, transverse colon.

Bouchoucha et al. characterized colonic transit time in 30 healthy subjects and in 43 patients with inflammatory bowel disease using X-ray opaque markers. The response to food was different in the two populations in controls, the cecum and ascending colon emptied and filled the distal bowel, whereas in the patients only the splenic flexure and left transverse colon emptied. Movement through both the right and left colon in patients was observed to be much slower than in controls, both before and after a meal [55]. 

The gas rises into the transverse colon and can form temporary pockets, which can restrict access of water to the formulation, particularly if the design does not permit uptake of water through the surface. For this reason, distal release of drug can be hampered by poor wetting/spreading and the reduced surface area, leading to restricted absorption. 

The anatomy of the distal colon, with its thick muscular walls, suggests a predominantly propulsive activity. Studies with single administrations of pellets or Pulsincap devices suggested that the distal part of the transverse colon area is difficult to treat since this area and the descending colon function as a conduit. Steady-state measurements confirm this assertion (48) and Weitschies group have also reported data showing mass movements propel objects quickly through the distal transverse colon. 

The pathways followed by the intestines are highly diverse, as is indicated, for example, by the variable positions of the transverse colon (Fig. 4). It will be noted that its position in some individuals is almost at the level of the sternum, but in others it is 10 to 12 in. lower. No particular position can be considered normal because about 30 per cent of the population is near one extreme or the other. In the other 70 per cent, various intermediate positions apply. 

More important possibly from the standpoint of function is the diversity of the anatomy of the pelvic colon itself. Figure 5 shows the various types of anatomical structures and the percentage occurrence of each. These percentages should be taken as indicative rather than accurate since they are based upon examination of only 210 specimens. If these percentages were accurate for the whole population of the United States, each of the least common forms (represented at the bottom of Figure 5) would exist in about 600,000 persons. It seems obvious that with this array of different types of pelvic colons (as well as transverse colons), people should differ tremendously (as they do) with respect to their problems of elimination. It is interesting to note in this connection that healthy newborn ba-... 

FIG. 1. Right, transverse, and left colon (adapted from Ref. 4). 

Tumor-promoting effect. A 28-year-old man who abused alcohol, nicotine, and cannabis for several years was investigated. He suffered simultaneously from a squamous cell carcinoma of the hypopharynx with bilateral cervical metastases, an adenocarcinoma of the transverse colon and a primary hepatocellular carcinoma. There were occurrences of three separate malignant tumors with different histologies in the aerodigestive tract, which could be related to a chronic abuse of cannabis . 

Human colon microsomal cytochrome P450 enzymes can demethylate 1,2-dimethylhydrazine, yielding formaldehyde, and activities in the descending colon are always higher than in the ascending or transverse colon (Newaz et al., 1983). A-Demethylation was also detected in microsomes from a human colon tumour line, adenocarcinoma LS 174T cells. The activity was inducible by phenobarbital and/or hydrocortisone. 

Most of the propulsion in the cecum and ascending colon results from the slow but persistent haustral contractions, requiring as many as 8 to 15 h to move the chyme only from the ileocecal valve to the transverse colon, while the chyme itself becomes fecal in quality and also becomes a semisolid slush instead of a semifluid. 

From the transverse colon to the sigmoid, mass movements take over the propulsive role. These movements usually occur only a few times each day, most abundantly for about 15 min during the first hour after eating breakfast. 

A mass movement is characterized by the following sequence of events. First, a constrictive ring occurs at a distended or irritated point in the colon, usually in the transverse colon, and then rapidly thereafter the 20 cm or more of colon distal to the constriction contract almost as a unit, forcing the fecal material in this segment en masse down the colon. During this process, the haustrations disappear completely. The initiation of contraction is complete in about 30 sec, and relaxation then occurs during the next 2 to 3 min before another mass movement occurs. But the whole series of mass movements will usually persist for only 10 min to half an hour, and they will then return perhaps a half day or even a day later. 

Mass movements can occur in any part of the colon, although most often they occur in the transverse or descending colon. When they have forced a mass of feces into the rectum, the desire for defecation is felt. 

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],... 

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