Intestinal villi

Fig. 4 Diagrammatic sketch of the small intestine illustrating the projection of the villi into the lumen (left) and the anatomic features of a single villus (right). (Modified from Ref. 7.)...

Figure 14 Ion transport pathways responsible for water flux across intestinal epithelia. Sodium absorption in villus tip cells (left) stimulates water absorption, while chloride channel exit in crypt cells (right) stimulates water secretion.

Bland, P.W. and Whiting, C.V. (1989) Antigen processing by rat intestinal villus enterocytes. Immunology 68, 497-502. 

Manson-Smith, D.F., Bruce, R.G. and Parrot, D.M.V. (1979) Villus atrophy and expulsion of intestinal Trichinella spiralis are mediated by T cells. Cellular Immunology 47, 285-293. 

In those infections that are associated with enteropathy (exemplified by T. spiralis), no experimental manipulation has, until recently, been able to separate enteropathy and immune expulsion - if one is abrogated, so is the other. This chapter illustrates how the two processes can be separated, and discusses implications of this for understanding immune expulsion of gut nematodes and the prospects for anti-nematode vaccines that cause no ill effects at either the initial induction of immunity or the expression of protective responses. The definition of that which consitututes enteropathy may vary between authors, but we take as our primary definition the most destructive and quantifiable changes in intestinal tissue that are associated with expulsion, villus atrophy and crypt hyperplasia. 

The morbidity and mortality that are often associated with human GI helminth infections reflect in part the nutritional consequences of diarrhoea and malabsorption, and the resulting malnutrition that can accentuate the effects of infection by suppressing the protective immune response as well as compromising intestinal repair (Ferguson et al., 1980 Keymer and Tarlton, 1991 Cooper et al, 1992). In experimental rodents the pathology associated with infection is characterized by villus atrophy, crypt hyperplasia, goblet cell hyperplasia and infiltration of the mucosa by a variety of... 

Fig. 18.3. Burdens of adult T. spiralis and development of intestinal pathology in mast-cell-deficient N/W mice. W/W mice and their normal littermates were infected with 400 T. spiralis muscle larvae. (A) Adult worm burdens are represented as mean + sem, five mice per group (, significantly different from day 6 p.i., P< 0.05). (B) Crypt and villus lengths were measured at day 0 and day 13 p.i. Results are expressed as mean + sem for five mice per group (, significantly different from uninfected animals (day 0), P< 0.05). Unpublished data.

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.

Fihn, B. M., A. Sjoqvist, and M. Jodal. Permeability of the rat small intestinal epithelium along the villus-crypt axis effects of glucose transport, Gastroenterology 2000, 119, 1029-1036... 

Intestine Extend exposure Adhere to villus tip Access ... 

Intestinal infections that cause persistent diarrhea normally result in histopathological changes to the intestine including villus blunting, crypt hypertrophy and inflammatory infiltrate in the lamina propria. These histopathological disarrangements are seen in Cryptosporidium, Cy-clospora and microsporidial infections [28], Furthermore, it has been documented that there are substantial disruptions of intestinal barrier function as measured by lactu-lose mannitol permeability ratios in patients with AIDS... 

However, the receptor-mediated endocytosis of iron-transferrin studies [63] does not explain the initial uptake of iron from nutrients in the intestinal (villus) cells, since apotransferrin is generally not available in the lumen, except in a limited amount from biliary excretion. Work on other iron transport mechanisms has mainly been reported in the last five years. 

Exposure of the intestinal cells to high concentrations of polyethylene glycol 2000 causes villus shortening, goblet cell capping, and destruction of the villus tip (35). The effects of smaller molecular weight materials were more extreme and... 

The amonnt of protein synthesised and then released in (iv) and (v) is abont 70 g each day. Even under conditions of starvation or malnutrition, proliferation and differentiation of stem cells located in the crypts of the villi are important to provide the cells necessary for replenishment of those lost from the villi. New cells move up the villus to replace those lost at the top. Under these conditions, amino acids are not available from the intestine and have to be taken up from the blood across the basolateral membrane. A low level of amino acids in the blood, due to chronic malnutrition, will prevent or reduce the rate of proliferation of these cells, so that digestion of even the small amount of food ingested during malnutrition, or refeeding after starvation, is difficult. A vicious circle thus results from protein-deficient diets which increase the risk of development of protein-energy-malnutrition. This is especially severe in children but may also contribute to the clinical problems that occur in the elderly whose diets are of low quality. 

The inner surface of the small intestine is not smooth and flat but wrinkled into a large number of finger-like projections called villi, which project into the lumen. If we look at each villus under the microscope (Fig. 1) we find it, in turn, has small fingerlike processes projecting out into the lumen - the microvilli. The result of this is that the surface of the small intestine (which is only 300 cm in length - in the relaxed state after death it may measure 6-7 metres), is estimated to have an area of 250 m. It is obviously designed to absorb, particularly, nutrients and this is also where most of any drug taken by mouth is absorbed. 

Epithelial cells of small intestine were prepared in a fractional way (4), the older, less adherent villus tip cells being washed out by EDTA-containing phosphate buffer first, while mitotic crypt cells appeared in the final fractions. The enzyme characteristics of the series of fractions obtained (Fig. 13) followed conventional criteria for differentiated (villus) and less differentiated (crypt) cells (3, 4). The thymidine kinase activity decreased from crypt to villus while the activity of alkaline phosphatase increased (Fig. 13). 

The large internal surface area of the small intestine is attributable to its length, folding, and the presence of villi and microvilli within its lumen. The villi contain capillaries and protrude into the lumen of the small intestine. There are approximately four to five million villi in the small intestine. Each villus has many microvilli as its outer surface (Figure 11.3). The microvilli represent the absorptive barrier of the small intestine. The stomach and large intestine do not contain villi and, therefore, have a small absorptive surface area compared with the small intestine. 

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