Gastrointestinal Tract - Postnatal

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Newborn infant

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.

GIT Links: Introduction | Medicine Lecture | Science Lecture | endoderm | mouth | oesophagus | stomach | liver | gallbladder | Pancreas | intestine | mesentery | tongue | taste | enteric nervous system | Stage 13 | Stage 22 | gastrointestinal abnormalities | Movies | Postnatal | milk | tooth | salivary gland | BGD Lecture | BGD Practical | GIT Terms | Category:Gastrointestinal Tract
GIT Histology Links: Upper GIT | Salivary Gland | Smooth Muscle Histology | Liver | Gallbladder | Pancreas | Colon | Histology Stains | Histology | GIT Development
Historic Embryology - Gastrointestinal Tract  
1878 Alimentary Canal | 1882 The Organs of the Inner Germ-Layer The Alimentary Tube with its Appended Organs | 1884 Great omentum and transverse mesocolon | 1902 Meckel's diverticulum | 1902 The Organs of Digestion | 1903 Submaxillary Gland | 1906 Liver | 1907 Development of the Digestive System | 1907 Atlas | 1907 23 Somite Embryo | 1908 Liver and Vascular | 1910 Mucous membrane Oesophagus to Small Intestine | 1910 Large intestine and Vermiform process | 1911-13 Intestine and Peritoneum - Part 1 | Part 2 | Part 3 | Part 5 | Part 6 | 1912 Digestive Tract | 1912 Stomach | 1914 Digestive Tract | 1914 Intestines | 1914 Rectum | 1915 Pharynx | 1915 Intestinal Rotation | 1917 Entodermal Canal | 1918 Anatomy | 1921 Alimentary Tube | 1932 Gall Bladder | 1939 Alimentary Canal Looping | 1940 Duodenum anomalies | 2008 Liver | 2016 GIT Notes | Historic Disclaimer
Human Embryo: 1908 13-14 Somite Embryo | 1921 Liver Suspensory Ligament | 1926 22 Somite Embryo | 1907 23 Somite Embryo | 1937 25 Somite Embryo | 1914 27 Somite Embryo | 1914 Week 7 Embryo
Animal Development: 1913 Chicken | 1951 Frog

Some Recent Findings

  • Restricting microbial exposure in early life negates the immune benefits associated with gut colonization in environments of high microbial diversity [1] "Acquisition of the intestinal microbiota in early life corresponds with the development of the mucosal immune system. Recent work on caesarean-delivered infants revealed that early microbial composition is influenced by birthing method and environment. Furthermore, we have confirmed that early-life environment strongly influences both the adult gut microbiota and development of the gut immune system. Here, we address the impact of limiting microbial exposure after initial colonization on the development of adult gut immunity."
  • Gram negative bacteria are associated with the early stages of necrotizing enterocolitis.[2] In a mouse model of the disease "Citrobacter, Klebsiella, and Tatumella are associated with Necrotizing enterocolitis (NEC). Differential colonic bacteria were identified despite the lack of inflammatory mediator elevation traditionally associated with NEC. This suggests a temporal relationship between bacteria and inflammatory mediators such that alterations in gut microbiota are associated with early NEC, while inflammatory mediator elevation is associated with advanced NEC."

Small Intestine Length

Small intestine growth in length prenatally is initially linear during the first half pregnancy (to 32 cm CRL), followed by rapid growth in the last 15 weeks doubling the overall length.

Postnatally, growth continues rapidly but after 1 year slows again to a linear increase to adulthood.[3]

Age (weeks gestational age) Average Length (cm)
20 125
30 200
term 275
1 year postnatal 380
5 years 450
10 years 500
20 years 575

Table data based upon 8 published reports of necropsy measurement of 1010 guts.[3]

Links: Intestine Development

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.[4]

Signalling pathway: presence of ingested lipids - intestinal lipid sensors - signal to the brain - liver - 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 and Listeria.

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

cartoon Intestinal function and microbiota

Cartoon showing relationship between microbiota and intestinal functionCite error: Closing </ref> missing for <ref> tag | Mouse model analysis of colonic microbiota.[2] Mice with NEC (a) are compared to mice without NEC (b). * indicates statistically significantly more in mice with NEC. ** indicates statistically significantly more in mice without NEC.


Links: PubMed Health | MedlinePlus


  1. Restricting microbial exposure in early life negates the immune benefits associated with gut colonization in environments of high microbial diversity
  2. 2.0 2.1 <pubmed>21445365</pubmed>| PLoS One.
  3. 3.0 3.1 <pubmed>1752463</pubmed>| PMC1379160 | Gut.
  4. <pubmed>18401341</pubmed>


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Cite this page: Hill, M.A. (2019, December 13) 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