The Ontogeny of the Small Intestinal Epithelium

Abstract

The primary factors in feeding premature infants are dependent on the development and maturation of digestion and absorption. The maturation of digestive and absorptive functions of carbohydrates, proteins, fats, minerals, and vitamins in the young premature infant were determined in relation to availability of hydrolytic enzymes, such as lipases, proteases, amylases, glucosidases, and lactase. The feeding is dependent on the ability of the premature infant to secrete salivary enzymes, gastric acid, pepsin, pancreatic exocrine enzymes, the presence of enterohepatic circulation, and the hydrolytic and absorptive capacity of the entercocyte. To evaluate the complexity of the gut maturation process, we proposed a unified concept where the ontogeny of the gastrointestinal system is the result of the following four major determinants: genetic endowment, intrinsic developmental and biological clock, endogenous regulatory mechanisms, and environmental influences. The developmental clock represents a predetermined temporal sequence of happenings in ontogeny that is inherently controlled. By 20 weeks of gestation, the anatomic differentiation of the fetal gut has progressed to the extent that it resembles that of a newborn. Secretory and absorptive functions, however, develop at different rates; the intestinal absorptive process is only partially available before 26 weeks of gestation, whereas gastric and pancreatic secretion is only basal and can be stimulated only partially even in the full-term newborn period. Regulatory mechanisms control the expression of the genetic endowment at various stages in gastrointestinal development. Neural-hormonal factors play major roles in the ontogeny of the gut. Adrenalectomy, hypophysectomy, and thyroidectomy delay the development of the gut. Administration of glucocorticoids or thyroxine at the critical stage in maturation causes early appearance of enzymes within the intestine. Other hormones that are potentially important in regulating gastrointestinal development include cholecystokinin, gastrin, secretin, which have trophic effects on the gastrointestinal tract, and insulin, insulin-like growth factors, and epidermial growth factor. The development of gastrointestinal secretory function, particularly in response to hormonal stimulation, has received considerable attention. The degree of response of the target cell is determined not only by the amount of effective hormone reaching it but also by the number and affinity of receptors on its surface. Human newborns have high levels of gastrin in their sera, yet have low acid output. Exogenous gastrin is an ineffective stimulant despite the presence of seemingly "anatomically developed" parietal cells. It seems that neither endogenous nor exogenous gastrin has an effect on the target cell. If one accepts the role of circulating gastrin levels in the regulation of its own receptor, one can hypothesize the absence of a regulatory effect of gastrin in the newborn period. It was shown that hormonal regulation of migrating activity by mot...

Preliminary characterization of jejunocyte and colonocyte cell lines isolated by enzymatic digestion from adult and young cattle

“…A likely explanation for this absence of full differentiation could reside in the selection during the primocultures of lowly differentiated stem cells, which can multiply better than they can fully differentiate in vitro, as already discussed (Rusu et al, 2005). In the case of the calf jejunocytes, however, the low level of IAP activity compared to the adult jejunocytes is in agreement with the known immature state of newborn intestinal epithelium (Lebenthal and Lebenthal, 1999).…”

Necrotizing enterocolitis: A multifactorial disease with no cure

“…Immature motility patterns alter normal peristaltic activity and result in overgrowth of anaerobic bacteria in the small intestine with malabsorption of dietary nutrients [23] . In addition, to impaired intestinal motility, premature infants have not yet developed the ability to digest and absorb nutrients and incompletely digested molecules could contribute to intestinal injury [32,33] . Lebenthal and Lee [34] showed that the function of the exocrine pancreas is limited in infants and that pancreatic insufficiency may last through the first year of life.…”

Intestinal gene expression profiles of piglets benefit from maternal supplementation with a yeast mannan-rich fraction during gestation and lactation

“…Gastrin is responsible for acid secretion and maintenance of the gastric mucosa (Jain and Samuelson, 2006) while CCK promotes digestion through different independent mechanisms (Bragado et al, 1998;Williams, 2001;Thomas et al, 2003). Previous results support the importance of CCK and gastrin for the fetal (Xu and Cranwell, 1991) and neonatal (Lebenthal and Lebenthal, 1999) gastrointestinal development in pigs.…”

“…Gastrin is responsible for acid secretion and maintenance of the gastric mucosa (Jain and Samuelson, 2006) while CCK promotes digestion through different independent mechanisms (Bragado et al, 1998;Williams, 2001;Thomas et al, 2003). Previous results support the importance of CCK and gastrin for the fetal (Xu and Cranwell, 1991) and neonatal (Lebenthal and Lebenthal, 1999) gastrointestinal development in pigs.Signaling of chemokine C-X-C motif receptor 4 (CXCR4), a chemokine receptor in the G protein coupled receptor family, was activated as a consequence of maternal supplementation with MRF. Activation of CXCR4 suggests potential regulation of humoral immunity (Nie et al, 2004) since this receptor is expressed commonly by immune cells and, in response to binding its ligand SDF-1 (stromal cell derived factor 1), triggers the migration and recruitment of immune cells (Bleul et al, 1996;Cheng et al, 2000).…”