Surface absorption

By approximately 8 weeks after birth, the mminant has developed a fully functional mmen capable of extensive fermentation of feed nutrients (4). The rate of development of the mminal environment depends on the amount of milk consumed by the neonate in relation to its growth requirements, the avadabihty and consumption of readily digestible feedstuffs, and the physical form of the feedstuffs (4). The mmen develops much faster with hay than with milk (36). Concentrates, ie, high cereal grain diets, increase the absorptive surface of the mmen but mminal size and musculature develops much more slowly with a concentrate diet than with a forage diet (4). 

A = effective (projected) water-cooled absorption surface area (m ),... 

Fig. 73. IR emission spectra of KNO3 melt at 450X7. Curve l - Layer thickness - 0.05 mm, reflective surface Curve 2 - Layer thickness - -0.1 mm, absorptive surface Curve 3 - Layer thickness - 0.2 mm, absorptive surface (after Agulyartsky and Sakharov [342]).

With few exceptions, small particles of vegetable foods are generally stripped of their more accessible nutrients during digestion in the GI tract. In this way starch, protein, fat and water-soluble small components (sugars, minerals) are usually well absorbed. This is not always the case, however, for larger food particles or for molecules that cannot diffuse out of the celF tissue. Neither is it the case for the lipid-soluble components. These need to be dissolved in lipid before they can be physically removed from the cell to the absorptive surface, since the cell wall is unlikely to be permeable to lipid emulsions or micelles, and the presence of lipases will strip away the solvating lipid. 

The mechanism of diarrhea has not been clearly elucidated, but theories include a reduction in the absorptive surface along with impaired absorption owing to cellular damage, enterotoxigenic effects of a rotavirus protein, and stimulation of the enteric nervous system.43... 

The plicae circulares, or circular folds, form internal rings around the circumference of the small intestine that are found along the length of the small intestine. They are formed from inward foldings of the mucosal and submucosal layers of the intestinal wall. The plicae circulares are particularly well developed in the duodenum and jejunum and increase the absorptive surface area of the mucosa about threefold. Each plica is covered with millions of smaller projections of mucosa referred to as villi. Two types of epithelial cells cover the villi ... 

The goblet cells produce mucus. The absorptive cells, found in a single layer covering the villi, are far more abundant. Taken together, the villi increase the absorptive surface area another 10-fold. 

The gut wall within the small intestine is particularly well adapted for its role as an absorptive surface. Absorption rate is proportional to the area of the surface that is available for absorption. Thus, the internal surface of the small intestine is folded towards the lumen of the gut. This folding increases the surface area of the gut by approximately 3-fold. In this area, the gut wall is covered with many fingerlike projections called villi, and these provide a further 10-fold increase in surface area. In addition, the gut wall epithelial cells are polarized such that on the luminal surface there are millions of microvilli providing a further 20-fold increase in surface area for absorption. In all, these surface area modifications provide an absorptive area which is some 600-fold higher than would be provided by a simple cylinder. Thus, the estimated surface area of the human gut is approximately 200 m2 [1],... 

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],... 

Surgery, which reduces the stomach volume or absorptive surface of the alimentary tract, remains the most effective intervention for obesity. Although modern techniques are safer than older procedures and have an operative mortality of 1%, there are still many potential complications. Therefore, surgery should be reserved for those with BMI greater than 35 or 40 kg/m2 and significant comorbidity. 

Administration of activated charcoal as an absorptive surface for di-w-octylphthalate has been suggested (Stutz and Ulin 1992). If ingestion of large amounts of di-/ -octylphthalate has occurred, the administration of a cathartic, such as magnesium sulfate, has been shown to increase the elimination of the substance from the gastrointestinal tract (Stutz and Ulin 1992). 

Type of solution (aqueous vs. lipid) Rate of dissolution of solid drugs Concentrations of a drug present Blood flow to the site of absorption Surface area of absorption... 

The FTIR reflection spectra of lead diethyl dithiocarbamate was reported to show the characteristic absorption bands 900, 981,1088,1138,1200,1248,1320,1351, 1398 and 1460 cm (Pouchert, 1970). The FTIR reflection spectra of sodium diethyl dithiocarbamate adsorption on jamesonite at pH = 7.0 are shown in Fig. 4.49. It can be seen that the characteristic absorption surface is lead diethyl dithiocarbamate. Further, the effect of pulp potential on the adsorption of diethyl dithiocarbamate on jamesonite was examined and the results are shown in Fig. 4.50. At pH = 4.7 the diethyl dithiocarbamate adsorption on jamesonite is mainly of lead diethyl dithiocarbamate independent of potential in the range of 485 - 680 mV due to the occurrence of almost the same lead diethyl dithiocarbamate characteristic band. However, the intensity of the IR signals changes at various potential values. It demonstrates the intensity of the IR signals of the characteristic peak lead diethyl... 

Developmental differences in drug absorption between neonates, infants and older children are summarized in Table 1. It must be recognized that the data contained therein reflect developmental differences which might be expected in healthy pediatric patients. Certain conditions and disease states might modify the function and/or structure of the absorptive surface area(s). GI motility and/or systemic blood flow can further impact upon either the rate or extent of absorption for drugs administered by ex-travascular routes in pediatric patients. 

The large intestine has a considerably smaller absorptive surface area than the small intestine, but it may still serve as a site of drug absorption, especially for compounds that have not been completely absorbed from the small intestine. However, little absorption occurs... 

Absorption Decreased absorptive surface Decreased splanchnic blood flow Increased gastric pH Altered gastrointestinal motility Little change in absorption with age... 

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