Factors that Influence the Differentiation and Growth of Glands Associated with the Gastrointestinal Mucosa
Various factors influence the differentiation, growth, and function of the glands associated with the gastrointestinal mucosa and also play an important role in regulating and maintaining the balance between epithelial cell proliferation and loss of cells from the gastrointestinal mucosa. Although the nature of the activities of such substances in Didelphis is unknown, there appears to be no reason to believe that they function in any way different to those in other mammals. Differentiation and growth, as well as epithelial cell proliferation and loss, are influenced by luminal, dietary, neural, and hormonal factors. Preprogrammed intrinsic factors also may play an important role in the regulation of the processes. The effect of such factors on gastrointestinal differentiation and growth have been summarized in elegant reviews by Klein and McKenzie (1983a,b), and by Johnson (1987) and Henning (1987). These factors include hypophysial hormones or tissues under hypophysial control, endogenous gastrointestinal hormones from enteroendocrine cells, neurotransmitters from the enteric nervous system, factors present in luminal content (amniotic fluid, milk, or dietary factors), and intrinsic mechanisms such as prostaglandins and chalones. Gastrin-, CCK-, somatostatin-, BPP-, glucagon-, secretin, motilin-, GIP-, neurotensin-, and 5-HT-immunoreactive cells are present in the gastrointestinal mucosa of the newborn opossum (Krause et al. 1986, 1989b). Cells with neurotensin immunoreactivity are unique in that, although present in the proximal colon of the newborn, the cells disappear and a significant population is not seen again in the intestinal mucosa until the 74th postnatal day, just prior to weaning.
KeywordsPancreatic Acinar Cell Pancreatic Polypeptide Epithelial Cell Proliferation Bile Secretion Bile Canaliculus
Unable to display preview. Download preview PDF.