Gastrointestinal Tract - Postnatal

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This page is an introduction to postnatal gastrointestinal tract development. This nutritionally involves a change from prenatal placental vascular nutrition to postnatal oral colostrum/milk enteral nutrition (enteral = nutritient delivery as fluid into the gastrointestinal tract). Also look at the topic of Milk in relationship to neonatal nutrition. The postnatal gastrointestinal tract development is also about increased activity of the tract and associated organs as well as the populating with intestinal flora in the tract. This is also the pathway for initial passive immunity through absorption of maternal immunoglobulin from breast milk.

These notes should be read in conjunction with the related page on Milk and an understanding of prenatal Gastrointestinal Tract Development.

Some Recent Findings

Lipid Signalling

Lipids present in the intestine leads to a reduction in nutrient intake. Recent research has shown that lipids present in the intestine can also regulate endogenous nutrient production.[2]

Signalling pathway:

presence of ingested lipids

intestinal lipid sensors

signal to the brain


reduction in endogenous glucose production

Insulin-like Growth Factors

Some evidence to suggest that in preterm infants IGFBP-2 and IGF-II present in breast milk may have an important role in their early development.

  • insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs)

Gut Microorganism Population

The normal newborn gastrointestinal tract contains little if any microorganisms (commensal intestinal microbiota, microbiota, flora, microflora). Postnatally, the tract has to be populated by microorganisms, which are mainly anaerobic bacteria and then aerobic bacteria, but may also include yeast and fungi. The foregut comparatively has few microorganisms when compared to the midgut and hindgut.


There are several infectious pathogens that can populate the postnatal gut leading to a number of different diseases:

  • Escherichia coli (enterotoxigenic)
  • Shigella a gram-negative, non-spore forming rod-shaped bacteria infectious through poor hygeine and ingestion, fecal–oral contamination. (More? Dysentery)
  • Vibrio cholerae
  • Listeria


Treatment of other neonatal infections systemically with antibiotics can alter the bacterial population.

Links: Medical Microbiology - Microbiology of the Gastrointestinal Tract


  1. <pubmed></pubmed>
  2. <pubmed>18401341</pubmed>

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Cite this page: Hill, M.A. (2019, September 20) Embryology Gastrointestinal Tract - Postnatal. Retrieved from

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© Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G