UNSW Embryology

Beginnings, Growth and Development

© Dr Mark Hill (2010)

Acknowledgements

GIT Practical: Embryology of the Gastro-Intestinal Tract

6. Postnatal

Introduction

Birth leads to changes in many different systems. Within the context of this Practical class we will look at just a few GIT changes at birth and during the neonatal period (first 4 weeks). A complete understanding requires knowledge of several other systems (respiratory, cardiovascular).

Many of the associated GIT organs and the tract (both motor and secretory) functions have commenced function during the late fetal period.

The early GIT has a number of unique properties.

The GIT epithelium has receptors which help internalise antibodies present in maternal milk, to aid continued maternal passive immunisation, prior to establishment of the newborn immune system.

The intestinal tract also requires populating postnatally with microorganisms (flora) which are mainly bacteria aerobic and anaerobic, but may also include yeast and fungi. Treatment of infection with antibiotics can alter this bacterial population. (More? Gut Microorganisms)

The infant has many different signs that indicate a need for feeding: restless, crying, sucking fingers (or anything) close to mouth. Smell is also used to turn the head towards a source of milk.

I have included on this page some links to Nutrition information and also look at the Additional Resources for further readings. (More? Milk Notes | Postnatal Notes)

Meconium

As introduced in fetal development, meconium is formed from gut and associated organ secretions as well as cells and debris from the swallowed amniotic fluid. Meconium accumulates during the fetal period in the large intestine (bowel). It can be described as being a generally dark colour (green black) , sticky and odourless.

• Normally this meconium is defaecated (passed) postnatally over the first 48 hours and then transitional stools from day 4.
• Abnormally this meconium is defaecated in utero, due to oxygen deprivation and other stresses. Premature discharge into the amniotic sac can lead to mixing with amniotic fluid and be reswallowed by the fetus. This is meconium aspiration syndrome and can damage both the developing lungs and placental vessels.

Postnatal Abnormalities

• Absence or delayed passage of meconium may indicate conditions associated with meconium plugs or more seriously, Hirshsrung's disease (aganglionic colon).
• Delayed conversion to transitional stools may indicate a feeding issue.

Nutrition - Milk

Breast milk makes us mammals! The review article (abstract shown below) by Goldman in 2000 may provide a way of thinking about GIT and human milk.

Goldman AS. Modulation of the gastrointestinal tract of infants by human milk. Interfaces and interactions. An evolutionary perspective. J Nutr. 2000 Feb;130(2S Suppl):426S-431S. Review.

"Human milk contains agents that affect the growth, development and functions of the epithelium, immune system or nervous system of the gastrointestinal tract. Some human and animal studies indicate that human milk affects the growth of intestinal villi, the development of intestinal disaccharidases, the permeability of the gastrointestinal tract and resistance to certain inflammatory/immune-mediated diseases. Moreover, one cytokine in human milk, interleukin (IL)-10, protects infant mice genetically deficient in IL-10 against an enterocolitis that resembles necrotizing enterocolitis (NEC) in human premature infants.

There are seven overlapping evolutionary strategies regarding the relationships between the functions of the mammary gland and the infant’s gastrointestinal tract as follows:

1. certain immunologic agents in human milk compensate directly for developmental delays in those same agents in the recipient infant
2. other agents in human milk do not compensate directly for developmental delays in the production of those same agents, but nevertheless protect the recipient
3. agents in human milk enhance functions that are poorly expressed in the recipient
4. agents in human milk change the physiologic state of the intestines from one adapted to intrauterine life to one suited to extrauterine life
5. some agents in human milk prevent inflammation in the recipient’s gastrointestinal tract
6. survival of human milk agents in the gastrointestinal tract is enhanced because of delayed production of pancreatic proteases and gastric acid by newborn infants, antiproteases and inhibitors of gastric acid production in human milk, inherent resistance of some human milk agents to proteolysis, and protective binding of other factors in human milk
7. growth factors in human milk aid in establishing a commensal enteric microflora"

(More? Normal Development - Milk | American Society for Nutritional Sciences | WHO Nutrition | ABC - Diet and nutrition)

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.

(More? Medical Microbiology Microbiology of the Gastrointestinal Tract)

Infections

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

Antibiotics

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

Additional Resources

Listed below are a few suggested readings to think about the GIT system in different ways. Note these are not examinable or even required for this current class! (More? see Selected GIT References)

Look how big I have grown

UNSW Embryology Growth Charts

Milk, milk, glorious milk

UNSW Embryology Normal Development - Milk

• Oddy WH. The impact of breastmilk on infant and child health. Breastfeed Rev. 2002 Nov;10(3):5-18. Review
• Field CJ. The immunological components of human milk and their effect on immune development in infants. J Nutr. 2005 Jan;135(1):1-4. Review.

Preterm Baby Nutrition

• Klein CJ. Nutrient requirements for preterm infant formulas. J Nutr. 2002 Jun;132(6 Suppl 1):1395S-577S. Review.
• Marriott LD, Foote KD. Advances in the nutrition of preterm infants. J R Soc Health. 2003 Sep;123(3):159-64. Review.

Its not just about Baby Nutrition

• Zadik Z. Maternal nutrition, fetal weight, body composition and disease in later life. J Endocrinol Invest. 2003 Sep;26(9):941-5. Review.

Changes

• Veereman-Wauters G. Neonatal gut development and postnatal adaptation. Eur J Pediatr. 1996 Aug;155(8):627-32. Review.
• de Santa Barbara P, van den Brink GR, Roberts DJ. Development and differentiation of the intestinal epithelium. Cell Mol Life Sci. 2003 Jul;60(7):1322-32. Review.

Your gut has immune functions

• largest immune organ of the body, mucosal immune system
• Newburg DS, Walker WA. Protection of the neonate by the innate immune system of developing gut and of human milk. Pediatr Res. 2007 Jan;61(1):2-8. Review. PMID
• Forchielli ML, Walker WA. The role of gut-associated lymphoid tissues and mucosal defence. Br J Nutr. 2005 Apr;93 Suppl 1:S41-8. Review.
  

Your gut has an endocrine function

• Lee CS, Kaestner KH. Clinical endocrinology and metabolism. Development of gut endocrine cells. Best Pract Res Clin Endocrinol Metab. 2004 Dec;18(4):453-62. Review.

Next

That completes todays GIT Practical class. Spend some time now or later looking at the development of the associated GIT Organs. If you wish to learn more, the following linked pages cover additional material. Abnormalities | Background | Histology Or review a more detailed coverage of GIT development Gastrointestinal Notes ----------------- Introduction Overview Stage 13/14 Stage 13/14 3D Model Stage 22 Stage 22 3D Model Stage 22 Selected Highpower Stomach Intestine GIT Folding Liver Gall Bladder Spleen Pancreas Enteric Nervous System Tongue Taste Postnatal Milk Molecular Movies Abnormalities Ultrasound Gastroschisis References

Glossary

Use the alphabetical list below to find definitions of terms that are new to you or use the Google search window to search UNSW Embryology site.

Terms

colostrum - The maternal mammary gland secretion that occurs at birth which precedes the secretion of milk. (More? Normal Development - Milk | Integumentary Development - Mammary Glands)

commensalism - An association between individuals of two species in which one organism benefits without harming the other one.

cryptopatches - (CPs) An immune system structure, small clusters of lymphoid cells with an immature lymphocyte phenotype and dendritic cells found associated with the gastrointestinal tract.

enteral - Nutritient delivery as fluid into the gastrointestinal tract. Can be used to describe postnatal nutrition through milk as well as a clinical method for delivering nutrition to patients. (More? Postnatal Gastrointestinal Tract | Milk)

Escherichia coli - (E. coli) A common eubacterial resident of the human gut. (More? Gastrointestinal Tract Notes | Postnatal Gastrointestinal Tract Notes)

ghrelin - (Greek, leptos = thin) a polypeptide hormone produced in the gastrointestinal tract (stomach) that stimulates release of growth hormone from the anterior pituitary. Hormone which probably has a role in regulating appetite and energy balance. (More? Endocrine Other Endocrine Notes | Meier U, Gressner AM. Endocrine regulation of energy metabolism: review of pathobiochemical and clinical chemical aspects of leptin, ghrelin, adiponectin, and resistin. Clin Chem. 2004 Sep;50(9):1511-25.

herniated - The discription of the process of protrusion of an organ through a weak spot in the surrounding tissue. In normal development, herniated midgut, describes the gastrointestinal tract growth outside the abdominal wall prior to body wall growth. In abnormal development, abnormal protrusion of organs in the diaphragm, abdominal or groin areas (hiatal hernias or inguinal hernias). Occurs normally in the development of the gastrointestinal tract when the midgut is initially herniated at the umbilicus during embryonic development.

Hirschsprung's Disease - see intestinal aganglionosis

homeostasis - (Greek, homeo = like, similar + stasis = standing) Term used to describe the process of achieving a relatively stable internal environment. Often used in describing the changes required in the fetus to neonate transition following birth (parturition). (More? Birth Notes)

intestinal aganglionosis - (Hirschsprung's Disease, megacolon) Gastrointestinal tract abnormality due to a lack of enteric nervous system (neural ganglia) in the intestinal tract responsible for gastric motility (peristalsis). In general, its severity is dependent upon the amount of the GIT that lacks intrinsic ganglia, due to an earlier developmental lack of neural crest migration into those segments. (More? Intestinal Aganglionosis | Gastrointestinal Tract Abnormalities | Neural Crest Abnormalities)

jaundice - Yellow colouration of the skin caused by high levels of bilirubin in the body. Present to some extent in most newborns due mainly to the time taken for the newborn liver to develop and functionally process bilirubin. Jaundice can also occur with normally with breast feeding (breastfeeding jaundice) and abnormally as a sign of a range of newborn abnormalities (conditions increasing red blood cell number or interference with bilirubin processing/removal). (More? Medline Plus - Newborn jaundice)

lactation - (Latin lactans = suckling) production of milk through action of prolactin and other hormones on breast tissue. Therefore associated mainly with mammals. (More? Normal Development - Milk | Integumentary Development - Mammary Glands)

mammary gland - A specialised modified secretory gland producing milk in female mammals for neonatal nutrition. Note that milk production and neonatal nutrition through milk, define us as mammals. (More? Integumentary Development - Mammary Glands)

maternal passive immunity - Term used to describe the transfer of maternal antibodies to the fetus (through the placenta) and the neonate (through milk). (More? Placenta | Normal Development - Milk)

meconium - The gastrointestinal contents that accumulate in the intestines during the fetal period. This material is a mixture of liver bile and glandular secretions, amniotic fluid, and cellular debris. Meconium is also used to describe the first postnatal rectal discharge from the neonate. Fetal stress in the third trimester or at parturition can lead to premature meconium discharge, into the amniotic fluid and ingestion by the fetus (meconium aspiration syndrome) and damage to respiratory function. Damage to placental vessels meconium myonecrosis may also occur. (More? Birth | Gastrointestinal Tract Notes | Respiratory Notes)

meconium plug syndrome - (functional immaturity of the colon) Term used to describe a transient disorder of the newborn colon, which is characterized by delayed passage of meconium (more than 24 to 48 h), intestinal dilatation and yellow/green vomiting. More common in premature infants and can be determined by radiological dye study.

meconium aspiration syndrome - (MAS) Fetal stress in the third trimester, prior to/at/ or during parturition can lead to premature meconium discharge into the amniotic fluid and sunsequent ingestion by the fetus and damage to respiratory function. Damage to placental vessels meconium myonecrosis may also occur.

necrotizing enterocolitis - (Greek, nekros = corpse) Gastrointestinal tract pathology occurring postnatally in mainly in premature and low birth weight infants (1 in 2,000 - 4,000 births). The underdeveloped gastointestinal tract appears to be susceptible to bacteria, normally found within the tract, to spread widely to other regions where they damage the tract wall and may enter the bloodstream. Pathological cell death from extrinsic injury. Cell lyses releasing cytoplasmic contents which may also have a role in initiating an inflammatory response. (More? Gastrointestinal Tract Abnormalities | Medline Plus - Necrotizing Enterocolitis)

puerperal - pertaining to childbirth or the period immediately following birth. (More? Birth Notes)

Quick Links

Everything Medicine 2009 ----------------- Found - Intro Embryo Lecture Found - Intro Embryo Practical Found Expert Tutorial-Histology SH - Respiratory Lecture ----------------- BGD - GIT Lecture BGD - GIT Practical Prac1 GIT Manual PDF GIT Development GIT Abnormalities ----------------- BGD - Head Lecture BGD - Head Practical Prac6 Head Manual PDF Head and Neck Development Face Development Ear Development Face Abnormalities ----------------- BGD - Endocrine Lecture Endocrine Development Endocrine Abnormalities ----------------- BDG - Male/Female Lecture BGD - Male/Female Practical Prac12 Male/Female Manual PDF Genital Development Male Development Female Development Genital Abnormalities ----------------- BGD-B Full Prac Manual PDF BGD-B FAQs BGD Phase 2 - Tutorial CBL ILPs 2009 eMed ----------------- Week by Week Movies Audio Development Notes System Notes Gastrointestinal Notes ----------------- Introduction Overview Stage 13/14 Stage 13/14 3D Model Stage 22 Stage 22 3D Model Stage 22 Selected Highpower Stomach Intestine GIT Folding Liver Gall Bladder Spleen Pancreas Enteric Nervous System Tongue Taste Postnatal Milk Molecular Movies Abnormalities Ultrasound Gastroschisis References

Links

• Microbiology of the Gastrointestinal Tract

Comments

On this sixth (and final) Practical page are a number of links to resources relating to early postnatal GIT development.

This material is not as "visual" as earlier pages. You should also look at GIT abnormalites that now show their presence with the establisment of postnatal nutritional and digestive functions.

Note that while the pancreas is a GIT accessory organ with exocrine functions, it is not necessary at this stage to cover the widespead abnormality associated with its endocrine function (diabetes) which should be covered elswhere in another scenario.

These notes and linked materials have been prepared for Educational purposes only.

Next Mark Hill Practical:

Sexual Differentiation covers early stages of male female development differences.

Quick Movie Links

Movie of Human Embryo Growth (this shows a human embryo growing, all images are to scale)

Movie of Mouse Embryo Growth (this shows a mouse embryo growing)

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