Pediatric Nutrition in Practice

Gastrointestinal Development, Nutrient Digestion and Absorption 85

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 Tr ypsin

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.

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