Intestinal absorption morphology

JS Trier. Morphology of the epithelium of the small intestine. In CF Code, ed. Handbook of Physiology. Vol. Ill, Intestinal Absorption. Washington, DC American Physiological Society,1968, p. 1133. 

Madara, J.L. Functional morphology of epithelium of the small intestine. In Intestinal Absorption and Secretion Field, M., Raymond, A.F., Eds. American Physiological Society, 1991 IV, 83-120. 

Caco-2 cells, derived from a human colon adenocarcinoma, differentiate spontaneously when grown on plates or filters into a continuous monolayer of cells presenting morphological and functional characteristics typical of normal ileal enterocytes [41-43] with a pseudo-bmsh border membrane. In the differentiated form, the monolayer mimics in some respects the microvilli of the small intestine epithelial cells. However, as for all immortalized cell lines, several key enzymes present in the human small intestine in vivo either are not expressed or are expressed to different extents between clones. The Caco-2 model has been used to study the intestinal absorption of flavonoids [44—49]. The evidence for transport... 

Friedman, H. I., and Cardell, R. R., 1972b, Morphological evidence for the release of chylomicra from intestinal absorptive cells, Exp. Cell Res. 75 57. 

Scott-Harris M, Kennedy JG, Siegesmund KA and Yorde DE (1988) Relationship Between Distension and Absorption in Rat Intestine. Effect of Luminal Volume on the Morphology of the Absorbing Surface. Gastroenterology 94 pp 1164-117 ... 

Thus, the apparent membrane permeability characteristics of hydrophilic compounds listed in Table 3.4 indicate that colonic epithelium is different from small intestinal epithelium in selectivity, or size or density distribution of the paracellular pathway. This is further complicated because of the possible involvement of unidentified carriers or channels for some compounds, as suggested for glycerol and D-xylose. However, the colon-to-SI ratios of the apparent membrane permeability are generally comparable with (or lower than) those calculated considering the morphological surface area, suggesting that such factors are not in favor for colonic absorption in most cases. Matching... 

Examination of the bone marrow, although important, will only confirm that the hemopoiesis is megaloblastic. A deficiency of folic acid will also cause a megaloblastic anemia and it is not possible to identify the cause on the basis of morphology. A serum assay of both vitamins will usually indicate which is responsible. If the patient is vitamin B12 deficient, the next step is to carry out a vitamin B12 absorption test to confirm that the deficiency is due to a lack of intrinsic factor. Preferably this should not be done until the patient s vitamin B12 and hemoglobin levels have returned to normal, since the gastric and intestinal cells are also affected by a lack of vitamin B12 aborption may be less than optimal if it is attempted too early. Patients with pernicious anemia also have a histamine-fast achlorhydria and gastric atrophy. The disease appears to have an autoimmune basis and antibodies to intrinsic factor can be demonstrated in the serum of more than half of affected patients. 

In the small intestine, contact time with the absorptive epithelium is limited, and the small intestinel transit time is 3.5-4.5 h [32], The scintographic data show that many prolonged release products, particularly those intended for twice- or once-daily administration, actually release some of their drug contents in the colon where it may be absorbed into the systemic circulation for higher bioavailability. It is anticipated that conditions of dissolution, absorption, and metabolism in the distal portions of the intestine are different than in the proximal regions, due to differences in pH, lumen fluid, mucosal morphology, and motility. 

At least part of the impairment of iron absorption in riboflavin deficiency is a result of morphological changes in the intestinal mucosa, with hyperproliferation, an increased rate of enterocyte transit along the villi and a reduced number of (longer) villi and deeper crypts (Williams et al., 1996). 

Azone (l-Dodecylazacycloheptan-2-one) and related compounds have been studied as transdermal penetration and oral absorption enhancers. Although some efficacy has been shown, an emulsifying agent appears to be necessary for azone to penetrate the intestinal mucosal membrane in order to promote drug absorption. One study reported the absence of gross morphological damage after exposure of mucosa to azone but additional information on the effect of azone on overall mucosa structure is not avalable. 

A rational approach to understanding the GI absorption of peptides and proteins requires some knowledge of the GI tract such as morphology, function of different components of the cells, geometry, ultrastructure, biochemical processes, hydrodynamics in the intestinal lumen, and transport mechanisms. 

One exception to the poor absorption of intact proteins is that neonates have the ability to absorb intact proteins for a few days after birth. Absorption cells of the neonatal mammalian intestine are functionally and morphologically specialized for the uptake and transport of milk macromolecules. The newborn has low levels of proteolytic enzymes in the intestinal... 

Isoda, N., Tamada, K., Ido, K. and Sugano, K. (2005) Cdx2 specifies the differentiation of morphological as well as functional absorptive enterocytes of the small intestine. The International Journal of Developmental Biology, 49 (7), 867-871. 

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