Small Bowel Review: Part II

Abstract

M ajor scientific advances have been made over the past few years in the areas of small bowel physiology, pathology, microbiology and clinical sciences. An in-depth review of the small bowel is presented. Topics discussed are enterocyte proliferation and growth factors; amino acids, peptides and allergies; motility; salt and water absorption and secretion -diarrhea; vitamins and minerals; early development and late ageing of the intestine; and ethanol. ENTEROCYTE PROLIFERATIONAND GROWTH FACTORS Small intestinal cell proliferation has been reviewed (1). The structural and functional integrity of the small intestine is maintained by the steady state of cell turnover whereby cell loss from the villi is balanced by cell production in the crypts. Each small intestinal crypt is composed of a single clone of cells, and several crypts contribute to each jejunal villus. The dynamic process of cell proliferation, migration and extrusion results in continuous renewal of the intestinal epithelia about every three days in rodents and every five days in humans. The majority of cells in both the crypt and villus compartments are enterocytes that acquire differentiated functions as they migrate out of the crypt. Migration of enterocytes from crypts to villi is coincident with the appearance of the differentiated phenotype. Little information is available on the molecular mechanisms that regulate cell lineage commitment, cell-specific gene expression or the process of differentiation as cells migrate from crypts to villi.Trefoil peptides are a group of small peptides that play a role in the process of maintaining the balance between proliferation and cell loss. The peptide is directed to the mucosal surface, in conjunction with mucin and glycoproteins. These trefoil peptides are resistant to protease digestion and ABR THOMSON, JA THOMSON, MJ ROPELESKI, GE WILD. Small bowel review: Part II. Can J Gastroenterol 1996;10(4): 261-273. Major scientific advances have been made over the past few years in the areas of small bowel physiology, pathology, microbiology and clinical sciences. Over 1000 papers have been reviewed and a selective number are considered here. Wherever possible, the clinical relevance of these advances have been identified. Topics discussed are enterocyte proliferation and growth factors; amino acids, peptides and allergies; motility; salt and water absorption and secretion -diarrhea; vitamins and minerals; early development and ageing of the intestine; and ethanol effects.

Sodium tungstate decreases sucrase and Na+/d-glucose cotransporter in the jejunum of diabetic rats

“…In diabetic rats, intestinal absorption of glucose increases as a result of a rise in the number of glucose transporters (14,31). Our results confirm that diabetes increases the activity and expression of SGLT1 in rat jejunum.…”

Mind the gap—deficits in our knowledge of aspects impacting the bioavailability of phytochemicals and their metabolites—a position paper focusing on carotenoids and polyphenols

“…A poorly understood factor in bioavailability is the role of brush border membrane enzymes, i.e. maltase, lactase‐phlorizin‐hydrolase, sucrase‐isomaltase, and peptidases . Lactase‐phlorizin‐hydrolase may play a crucial role in cleaving polyphenol glycosides, resulting in the uptake of free aglyones .…”

“…Prior to reaching the cellular surface, diffusion through the mucus is required, though properties influencing diffusion are poorly understood. Viscosity and particle/micelle size of the digesta are expected to play a role.…”

The effects of long-term total parenteral nutrition on gut mucosal immunity in children with short bowel syndrome: a systematic review

“…Thomson and colleagues [40-42], citing various sources, suggest that enterocytes function as "nonclassical" immune cells, which play a major role as a source of proinflammatory cytokines and cytotoxins. A key proinflammatory mediator produced in intestinal mucosa is the free radical nitric oxide.…”