Trahair J F, Sangild P T
Department of Anatomy and Histology, University of Adelaide, South Australia.
Equine Vet J Suppl. 1997 Jun(24):40-50. doi: 10.1111/j.2042-3306.1997.tb05077.x.
At birth, the mammalian gastrointestinal tract (GIT) must be able to support a shift from mainly parenteral nutrition in the fetus (via the placenta) to enteral nutrition in the neonate. In the perinatal period the GIT therefore undergoes enhanced growth as well as morphological and functional differentiation, and this maturational programme is influenced by a complex interplay of local, systemic and luminal factors. This review shows how systemic and luminal factors may influence GIT development in the perinatal period of the pig and sheep, two long-gestation species. Adrenocortical hormones play a pivotal role in the prepartum maturation of the GIT in addition to their better known effects on the development of many other tissues and body systems. More particularly, in the fetal pig and sheep, the prenatal development of gastric acid and gastrin secretion, and of GIT hydrolase activities (chymosin, pepsin, amylase, lactase, aminopeptidases) is influenced by cortisol. Additionally, glucocorticoids exert effects throughout the GIT by influencing morphological, cytological, and functional differentiation. Since the GIT epithelial cells comprise a renewing cell population there are also changes in cell kinetics. In addition to systemic factors, the presence of growth factors, hormones and nutrients from swallowed amniotic fluid (fetus) and colostrum (neonate) may influence GIT development. In utero, fetal fluid ingestion has been shown to modulate tissue growth, macromolecule and immunoglobulin transport, enterocyte differentiation, cell turnover and activity of brush-border hydrolases. These effects may be mediated via regulatory peptides (e.g. insulin-like growth factor I, gastrin-releasing peptides, insulin, epidermal growth factor, gastrin). A physiological role of luminally derived growth factors is supported by a number of unique structural and functional adaptations of the GIT in the fetus and neonate (low luminal proteolysis, intestinal macromolecule transport). Thus, in the pig and sheep, both systemic and luminal factors appear to play critical roles in GIT development in the perinatal period.
出生时，哺乳动物的胃肠道（GIT）必须能够支持从胎儿期主要通过胎盘进行的肠外营养向新生儿期肠内营养的转变。因此，在围产期，胃肠道会经历生长加速以及形态和功能分化，而这一成熟过程受到局部、全身和腔内因素的复杂相互作用的影响。本综述展示了全身和腔内因素如何影响猪和羊这两种妊娠期较长的物种在围产期的胃肠道发育。肾上腺皮质激素除了对许多其他组织和身体系统的发育有众所周知的影响外，在胃肠道产前成熟过程中也起着关键作用。更具体地说，在胎儿猪和羊中，胃酸和胃泌素分泌以及胃肠道水解酶活性（凝乳酶、胃蛋白酶、淀粉酶、乳糖酶、氨肽酶）的产前发育受皮质醇影响。此外，糖皮质激素通过影响形态、细胞学和功能分化，在整个胃肠道发挥作用。由于胃肠道上皮细胞构成了一个不断更新的细胞群体，细胞动力学也会发生变化。除了全身因素外，来自吞咽羊水（胎儿）和初乳（新生儿）中的生长因子、激素和营养物质的存在也可能影响胃肠道发育。在子宫内，已证明胎儿摄入羊水可调节组织生长、大分子和免疫球蛋白转运、肠上皮细胞分化、细胞更新以及刷状缘水解酶的活性。这些作用可能通过调节肽（如胰岛素样生长因子I、胃泌素释放肽、胰岛素、表皮生长因子、胃泌素）介导。胎儿和新生儿胃肠道的一些独特结构和功能适应性（低腔内蛋白水解、肠道大分子转运）支持了腔内源性生长因子的生理作用。因此，在猪和羊中，全身和腔内因素在围产期胃肠道发育中似乎都起着关键作用。
