Small bowel absorption

PTH stimulates demineralization of bone and release of calcium and phosphate into the blood by stimulating osteoclast formation and activity, increases small bowel absorption of calcium ion, and acts directly on the kidney to suppress calcium ion excretion in the urine. 

Papadia, C., Sherwood, R.A., Kalantzis, C., Wallis, K., Volta, U., Fiorini, E., and Forbes, A. 2007. Plasma citrulline concentration a reliable marker of small bowel absorptive capacity independent of intestinal inflammation. Am J Gastroenterol, 102(7) 1474-1482. 

The food, now in a liquid form known as chyme, passes through the pyloric sphincter into the duodenum, where stomach acid is neutralized. There is wide variation in lengths of the components of the small intestine (i.e., duodenum, jejunum, and ileum) between individuals (Table 98-1). Most absorption of digested carbohydrate and protein occurs within the jejunum. Most fat absorption occurs within the jejunum and ileum. In the small bowel, breakdown of macronutrients (i.e., carbohydrate, protein, and fat) occurs both within the lumen of the gut and at the intestinal mucosal membrane surface. The absorptive units on the intestinal mucosal membrane are infoldings known as... 

After absorption in the small bowel, remaining undigested food passes from the ileum through the ileocecal valve to the colon. A major role of the colon is absorption of fluid. Some of the water and sodium absorption achieved by the colon is facilitated by short-chain fatty acids (SFCAs) formed from digestion of certain dietary fibers by colonic bacterial enzymes. 

The location of the tip of the feeding tube is important when considering medication administration down a feeding tube. This is particularly true if the medication acts locally in the GI tract itself. For example, sucralfate and antacids act locally in the stomach. Therefore, administration of these medications through a duodenal or jejunal tube is not logical. Likewise, for medications such as itraconazole that require acid for best absorption, administration directly into the duodenum or jejunum would be expected to result in suboptimal absorption. Absorption of drugs when administered directly into the small bowel, especially the jejunum, rather than into the stomach is another area where more research would be useful. 

Malabsorption in SIBO is considered the consequence of abnormalities occurring mainly in the intraluminal environment in fact, the excessive number of intraluminal bacteria interfere with the absorption process. However, in some cases, the presence of bacterial species capable of more aggressive adhesion to small bowel epithelium is probably the cause of direct damage to the absorptive surface, in particular in the blind loop syndrome [10,11],... 

Normen L, Dutta P, Lia A and Andersson H. 2000. Soy sterol esters and 3-sitostanol ester as inhibitors of cholesterol absorption in human small bowel. Am J Clin Nutt 71(4) 908—913. 

Holgate AM, Read NW. Relationship between small bowel transit time and absorption of a solid meal. Dig Dis Sci 1983 28(91 812-819. 

Kavin H, Levin NW and Stanley MM (1967) Isolated Perfused Rat Small Bowel—Technic Studies of Viability Glucose Absorption. J Appl Physiol 22 pp 604-611. 

In the colon, semifluid material entering from the small bowel is thickened by absorption of water and salts (from about 1000 to 150 mL/d). If, due to the action of an irritant purgative, the colon empties prematurely, an enteral loss of NaCl, KCl and water will be incurred. To forestall depletion of NaCl and water, the body responds with an increased release of aldosterone (p. Ltillmann, Color Atlas of Pharmacology... 

Physiologically, this vitamin, after absorption, which takes place throughout most of the small bowel, is inextricably linked to its co-enzyme vitamin B12 and they share a final common pathway culminating in the optimum synthesis of deoxyribonucleic acid. 

Antimotility drugs are opioid drugs. They increase small bowel smooth muscle tone and segmentation activity. They also reduce propulsive movements and decrease intestinal secretions while increasing absorption. They mediate these actions through p receptors. 

Overdosage and underdosage relative to the prescribed dosage—both aspects of failure of compliance—can frequently be detected by concentration measurements when gross deviations from expected values are obtained. If compliance is found to be adequate, absorption abnormalities in the small bowel may be the cause of abnormally low concentrations. Variations in the extent of bioavailability are rarely caused by irregularities in the manufacture of the particular drug formulation. More commonly, variations in bioavailability are due to metabolism during absorption. 

Drugs that contain 5-aminosalicylic acid (5-ASA) have been used successfully for decades in the treatment of inflammatory bowel diseases (Figure 62-8). 5-ASA differs from salicylic acid only by the addition of an amino group at the 5 (meta) position. Aminosalicylates are believed to work topically (not systemically) in areas of diseased gastrointestinal mucosa. Up to 80% of unformulated, aqueous 5-ASA is absorbed from the small intestine and does not reach the distal small bowel or colon in appreciable quantities. To overcome the rapid absorption of 5-ASA from the proximal small intestine, a number of formulations have been designed to deliver 5-ASA to various distal segments of the small bowel or the colon. These include sulfasalazine, olsalazine, balsalazide, and various forms of mesalamine. 

Intestinal absorption studies of Mn-MP were undertaken in an effort to assess the viability of the metalloporphyrin as an oral hepatobiliary agent [101, 102]. Mixed micelles of Mn-MP complexed with monoolein and taurocholate were administered to rats, resulting in liver image enhancement 68% above baseline levels six hours after administration [101]. In pigs, the mixed micelle preparation showed variable enhancement over 24 hours. Observation that Mn-MP interacts with oleic acid vesicles [103] led to investigations of the effect of oleic acid on the absorption rate of Mn-MP from the small bowel into the circulatory system [102,104]. The increase in absorption of the complex was mediated by a decrease in the relaxivity of the metalloporphyrin resulting from the interaction with the lipid vesicles. 

Normen, L., Dutta, P., Lia, A., and Andersson, H. 2000. Soy sterol esters and beta-sitostanol ester as inhibitors of cholesterol absorption in human small bowel. Am. J. Clin. Nutr. 71, 908-913. Normen, L., Brants, H. A. M., Voorrips, L.E., Andersson, H.A., van den Brandt, P.A., and Gold-bohm, R.A. 2001. Plant sterol intakes and colorectal cancer risk in the Netherlands cohort study on diet and cancer. Am. J. Clin. Nutr. 74, 141-148. 

The pharmacokinetics of XYZ1234 formulations after release in different regions of the gastrointestinal tract reveal similar exposure for the proximal small bowel as compared to the immediate release formulation, halved exposure for the distal small bowel and only poor absorption from the ascending colon. Thus colonic resorption cannot be relied on for the development of an extended release formulation. Analysis of the scintigraphic data has confirmed release of the formulation at the target locations in the required number of subjects. 

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