Michael J. Lentze
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84 Lentze
the first tube has a length of 4 mm from the mouth to the cloaca. During pregnancy, it elon- gates about 1,000-fold until full term. The sto m- ach at term has a volume of about 30 ml, the small intestine a length of 250–300 cm, the large intes- tine a length of 30–40 cm. Between the 9th week of gestation and birth, the small intestine under- goes extraordinary changes from a primitive strat- ified epithelium of undifferentiated epithelial cells into a fully differentiated organ with villi and crypts [1] . The formation of Peyer’s patches starts at 16–18 weeks of gestation when the first lympho- cytes are seen in the lamina propria [2] .
Parallel to the morphological changes during fetal development, the digestive and absorptive functions of the gastrointestinal tract begin to
appear at the 10th week of gestation and fully ex- press their activities between the 26th week of gestation and term, or within the first month of life.
The brush border enzymes lactase, maltase- glucoamylase and sucrase-isomaltase are first de- termined at the 10th week of gestation ( fig. 1 ).
Whereas sucrase-isomaltase reaches its full ac- tivity already by the 25th week of gestation, lac- tase activity is fully developed by the 32nd week of gestation [3, 4] . As lactose is the predominant sugar in breast milk, the possibility exists that premature babies born before the 32nd week of gestation might lack full lactase activity when fed breast milk or a lactose-containing premature formula. However, the overall lactase activity
0 5
Detection of first activity Full activity
10 15 20 25 30 35 40
BBM peptidases Weeks of gestation
Lactase Maltase-glucoamylase
Sucrase-isomaltase
Prematures
<1,500 g SGLT1, GLUT5
Amino acid transporters Peptide transporters
Fig. 1. Development of brush border enzymes and transporters during fetal life. BBM = Brush border membrane; SGLT1 = sodium-dependent glucose transporter 1; GLUT5 = glucose transporter 5.
Koletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 83–86 DOI: 10.1159/000360320
1
along the small intestine even in VLBW infants is sufficient to hydrolyze lactose into glucose and galactose.
The transport system responsible for the up- take of glucose and galactose, the sodium-de- pendent glucose transporter 1, is already fully active by the 25th week of gestation, as is glucose transporter 5 [5] . For the digestion of proteins, the pancreatic enzymes trypsin, chymotrypsin and carboxypeptidase are first detected in the 24th week of gestation ( fig. 2 ). Full activity is reached by the 26th week of gestation. Trypsino- gen is activated by enterokinase in the 24th week of gestation. The brush border peptidases, the amino acid transporters as well as peptide trans- porters start their transport activities at the 10th week of gestation and reach their full activity by 25th week of gestation [6] . The digestion of pro- teins and the absorption of amino acids and di- peptides are effective already in VLBW infants.
Fat digestion depends on various lipases and the formation of micelles. The responsible lipases,
such as gastric and pancreatic lipases, show their first measurable activities at the 24th week of gestation. Full enzyme activity develops steadily toward term and after birth. Depending on the type of food, breast milk lipase given to infants by breastfeeding supplements fat digestion dur- ing the first weeks of life [7] . The digestion of starch is the last to develop during pregnancy and after birth. Pancreatic amylase is first de- tected in the 22nd week of gestation, but reaches its full activity as late as the 6th month after birth. Premature or term infants cannot easily digest large amounts of starch. Small amounts of starch, however, can be given to premature and term infants without difficulty because amylose and amylopectin are also hydrolyzed by the ac- tion of sucrase-isomaltase and maltase-glu- coamylase [8] .
Although the digestive and absorptive capa c- ity of the gastrointestinal tract is well prepared for external life after birth even in premature ba- bies, immature motility is the limiting system
20 22 24 26 28 30 32 40 6
Weeks of gestation Enterokinase
Amylase Gastric lipase
Pancreatic lipase Trypsinogen Trypsin
Prematures
<1,500 g Breast milk: bile salt-stimulated lipase
Months
Detection of first activity Full activity
Fig. 2. Development of pancreatic enzymes, gastric lipase and enterokinase during fetal life.
86 Lentze
particularly in premature infants coping with ex- ternal feeding. Here, the response of the intestine to a bolus feed depends on the maturity of the gut. In small infants before 31 weeks of postcon- ceptional age, who usually receive low volumes of continuous enteral feed, ordinary postprandial activity does not occur [9] . Between 31 and 35 weeks of postconceptional age, postprandial ac- tivity is induced in infants by giving them larger volumes of feed. However, the activity remains in a fasting pattern with superimposed, more ran- dom postprandial activity. Finally, in infants over 35 weeks of postconceptional age who receive large volumes of bolus feed, there is a disruption in cyclical fasting activity and replacement by continuous activity. Whether this motility pat- tern can be advanced by pharmacological mea- sures such as the administration of cortisol re- mains to be seen [10, 11] .
Conclusions
Feeding of premature infants below 35 weeks of gestation requires knowledge of physiological functions at this time. Whereas digestive and ab- sorptive functions are mostly developed from the 24th week of postconceptional age, gastrointestinal motility is still not very active. Premature formulas or fortified breast milk can be given to VLBW in- fants or extremely LBW infants in small quantities.
From the 31st postconceptional week onward, the quantity of enteral feeds becomes less of a problem.
As far as macronutrients are concerned, protein is digested and absorbed well. Carbohydrates, in form of lactose, are also digested and absorbed well. Starch can only be digested in small quanti- ties. The digestion of fat increases quickly from the 26th week of gestation and can be enhanced by ad- ministration of milk lipase via breast milk.
8 Terada T, Nakanuma Y: Expression of pancreatic enzymes (α-amylase, tryp- sinogen, and lipase) during human liver development and maturation. Gastro- enterology 1995; 108: 1236–1245.
9 Bisset WM, Watt J, Rivers RP, Milla PJ:
Postprandial motor response of the small intestine to enteral feeds in pre- term infants. Arch Dis Child 1989; 64:
1356–1361.
10 Bisset WM, Watt JB, Rivers RP, Milla PJ:
Ontogeny of fasting small intestinal mo- tor activity in the human infant. Gut 1988; 29: 483–488.
11 Bisset WM, Watt JB, Rivers RP, Milla PJ:
Measurement of small-intestinal motor activity in the preterm infant. J Biomed Eng 1988; 10: 155–158.
References
1 Moxey PC, Trier JS: Development of villous absorptive cells in the human fetal small intestine: a morphological and morphometric study. Anat Rec 1979; 195: 463–482.
2 Owen WL, Jone AL: Epithelial cell spe- cialisation within human Peyer’s patch- es: an ultrastructural study of intestinal lymphoid follicles. Gastroenterology 1974; 66: 189–203.
3 Lentze MJ: Die Ernọhrung von Frỹhge- borenen unter 1,500 g: Enterale Voraussetzungen. Monatsschr Kinder- heilkd 1986; 134: 502–507.
4 Menard D: Development of human in- testinal and gastric enzymes. Acta Pae- diatr Suppl 1994; 405: 1–6.
5 Davidson NO, Hausman AM, Ifkovits CA, Buse JB, Gould GW, Burant CF, Bell GI: Human intestinal glucose transport- er expression and localization of GLUT5. Am J Physiol 1992; 262:C795–
C800.
6 Adibi SA: Regulation of expression of the intestinal oligopeptide transporter (Pept-1) in health and disease. Am J Physiol Gastrointest Liver Physiol 2003;
285:G779–G788.
7 Boehm G, Bierbach U, Senger H, Jakobs- son I, Minoli I, Moro G, Rọihọ NC: Ac- tivities of lipase and trypsin in duodenal juice of infants small for gestational age.
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324–327.
Koletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 83–86 DOI: 10.1159/000360320
1 Specific Aspects of Childhood Nutrition
Key Words
Microbiota ã Probiotics ã Prebiotics ã Health
Key Messages
• A healthy microbiota preserves and promotes host wellbeing and absence of disease in general – not only in the gastrointestinal tract
• Colonization of the infant by microbes is initiated during pregnancy
• Initial colonization by ‘pioneer bacteria’ is en- hanced by both naturally occurring bacteria and oligosaccharides in breast milk
• These pioneer bacteria direct later microbiota suc- cession, forming a basis for a healthy gut microbio- ta throughout one’s lifetime
• The microbiota resembles that of adults by 2–3 years of age
• Disturbed microbiota succession during early in- fancy has been linked to increased risk of infectious, inflammatory and allergic diseases later in life • Intestinal microbial colonization and its modula-
tion by dietary means are important considerations during the first years of life
© 2015 S. Karger AG, Basel
Initial Establishment of Microbiota
Source of Original Microbiota
The microbiota of a newborn is acquired from the mother before and after birth and develops rapidly following delivery. It is initially strongly depen- dent on the mother’s microbiota, the mode of de- livery and the birth environment [1, 2] . The micro- biota of the mother is determined by genetic and environmental factors. Stress and dietary habits during later pregnancy have a significant impact on the microbiota. Even in healthy pregnancy, the maternal microbiota changes considerably be- tween the 1st and the 3rd trimester [3] . Such changes influence the quality and quantity of the initial colonizers of the newborn. Subsequently, feeding practices (formula or human milk) and the infant’s home environment influence microbiota succession at the genus and species level, as well as species composition and numbers of bacteria.
Succession of Microbial Communities
Establishment of the microbiota in the newborn occurs in a stepwise fashion. Studies on mice have shown that the first bacteria to colonize the intes- tine, even prior to delivery and during the perina- tal period (‘pioneer bacteria’), can modulate gene expression in host intestinal epithelial cells. This
Koletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 87–91 DOI: 10.1159/000360322