Intestine lumen

Figure 3. Section of intestine from fetus whose mother was dosed orally with 1 fj g/kg/day of 2,3,7,8-tetrachlorodihenzo-p-dioxin during gestation days 6-15 (Note hemorrhage in intestinal lumen) (lOOX)...

Both influx and efflux transporters are located in intestinal epithelial cells and can either increase or decrease oral absorption. Influx transporters such as human peptide transporter 1 (hPEPTl), apical sodium bile acid transporter (ASBT), and nucleoside transporters actively transport drugs that mimic their native substrates across the epithelial cell, whereas efflux transporters such as P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and breast cancer resistance protein (BCRP) actively pump absorbed drugs back into the intestinal lumen. 

Dietary fats, libers, and other carotenoids have been reported to interfere with carotenoid bioaccessibility. It is clear that by their presence in the gut, lipids create an environment in favor of hydrophobic compounds such as carotenoids. When arriving in the small intestinal lumen, dietary fats stimulate bile flow from the gallbladder and therefore enhance the micelle formation, which in turn could facilitate the emulsification of carotenoids into lipid micelles. Without micelle formation, carotenoids are poorly absorbed a minimum of 3 g of fat in meal is necessary for an efficient absorption of carotenoids, except for lutein esters that require higher amounts of fat. ... 

Osmotic diarrhea results from the intake of unabsorbable but water-soluble solutes in the intestinal lumen leading to water retention. Common causes include lactose intolerance and ingestion of magnesium-containing antacids. 

Secretory diarrhea results in an increase in the net movement (secretion) of ions into the intestinal lumen leading to an increase in intraluminal fluid. Medications, hormones, and toxins may be responsible for secretory activity. 

Inflammatory (or exudative) diarrhea results from changes to the intestinal mucosa that damage absorption processes and lead to an increase in proteins and other products in the intestinal lumen with fluid retention. The presence of blood or fecal leukocytes in the stool is indicative of an inflammatory process. The diarrhea of inflammatory bowel disease (e.g., ulcerative colitis) is inflammatory in nature. 

Physical/mechanical (e.g., tumor compressing intestinal lumen) Functional (e.g., postoperative ileus)... 

Translocation Movement of bacteria and endotoxin from the intestinal lumen through the gut mucosa and into the lymphatic and systemic circulation. 

Niess JH, Brand S, Gu X, et al. CX3CR1-mediated dendritic cell access to the intestinal lumen and bacterial clearance. Science 2005 307(5707) 254-258. 

In case III, solid drug exists at both inlet and outlet. The concentration in the intestinal lumen can be assumed to be equal to the solubility ... 

From Eq. (12), the dependence of Fa on both An and Do is apparent. The relationship suggests that a lower fraction of dose will be absorbed at a higher dose. However, for compounds with low solubility and/or high dose, the concentration in the intestinal lumen may not be the same as the solubility, owing to slow dissolution. Dissolution-limited absorption is discussed in Section III.B. 

Thus, in contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of the intestinal carotenoid absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (TC OA supplementation), differentiated Caco-2 cells were able (1) to take up carotenoids at the apical side and to incorporate them into CM and (2) to secrete them at the basolateral side, associated with CM fractions. In this model, no attempt has yet been made to reproduce the in vivo physiochemical conditions occurring in the intestinal lumen, such as carotenoid release from the food matrix and solubilization into mixed lipid micelles. Carotenoids were delivered to Caco-2 cells in aqueous suspension with Tween 40 (During et al., 2002). Using this cell culture system in conjunction with an in vitro... 

Figure 8.2 Rat duodenal cells divide in the crypts of Lieberktihn and differentiate while migrating to the villus tips within approximately 48 h. The crypt cells take up iron from the blood, and are thereby able to sense the body s state of iron repletion. They migrate to the villus tips where this information determines their iron absorption capacity from the intestinal lumen. Adapted from Schumann et al., 1999, by permission of Blackwell Science.

A4 in the human enterocyte. Both the parent drug and its metabolite, R/S-norverapamil, can be transported into the blood or back into the intestinal lumen. 

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