Isolated ileal interposition in enteroendocrine L cells differentiation

function. It is clear that genes regulating cell cycle, proliferation, differentiation, and apoptosis
are important components of the adaptation process (Drozdowski et al., 2009). 97 Several
studies in humans and laboratory animals showed that after massive resection of the proximal
small intestine, the remaining ileum exhibits morphological and functional adaptation in an
attempt to preserve nutritional health by increasing ileal absorption of dietary nutrients. The
authors of these studies concluded that the ileal adaptation mechanisms for peptide
absorption are mediated by cell proliferation, i.e., villus hyperplasia and intestinal dilatation,
which serves to increase the absorption surface. 115
Gastrointestinal epithelial cells are under constant regenerative pressure. To maintain
Nature Precedings : doi:10.1038/npre.2011.6614.2 : Posted 30 Nov 2011
homeostasis, there must be a balance among cell apoptosis, senescence, proliferation, and
differentiation. The maintenance of this balance is attributed to gastrointestinal stem cells.
These cells are able to replicate and give rise to cells identical to themselves and to cells that
will differentiate into each of the different cell types present in this tissue. 116 Small numbers of
intestinal stem cells (between one and three) are found at the bottom of each of the
Lieberkühn crypts, which are the invaginations that make up the intestine’s proliferative
component. These cells give rise to a transient population of progenitor cells, which divide
quickly while migrating along villi towards the bowel lumen. During migration, these cells
commit to one of three different cell lineages: secretory (goblet cells), absorptive
(enterocytes), or enteroendocrine. This is a continual process in which the most differentiated
cells are replaced at the top of the villi every four or five days. Another type of secretory cell,
called Paneth cells, differentiates at the bottom of the crypts (Figure 2). 117