BGDB Gastrointestinal - Postnatal

From Embryology
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Practical 1: Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Lecture | Quiz

Birth

Newborn infant
Newborn infant

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). Remember that the GIT as well as digestion and absorption of nutrients also has endocrine, neural and immunological functions.

Gutherie card icon.jpg Guthrie test Issues related to metabolic disorders will be covered in GIT Abnormalities.


  • The first stool (meconium) is passed within 24 hours in most healthy term infants.
    • often delayed in infants with very low birth weight and may not occur until 1 week after birth or later.
  • Many of the associated GIT organs and the tract (both motor and secretory) functions have commenced function during the late fetal period and the early neonatal 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)
  • Abnormalities of face development (cleft lip and cleft palate) can affect the ability of the infant to feed, a "liquid seal" is formed by the mouth during feeding. (Clefting will be covered in Face Development Practical)

Meconium

Meconium aspiration syndrome x-ray

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.

  • 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.

Meconium Aspiration Syndrome

  • 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, Hirshsprung's disease (aganglionic colon, megacolon).
  • Delayed conversion to transitional stools may indicate a feeding issue.

Nutrition - Milk

Adult female mammary anatomy cartoon

Breast milk makes us mammals! A review article by Goldman[1] may provide a way of thinking about GIT and human milk.

"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"

(Text from: Goldman ref[1])


Links: Normal Development - Milk

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.


Links: 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
  • Listeria

Antibiotics

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

Necrotizing Enterocolitis

  • (NEC) is a disease affecting infants born prematurely, affects 5–10% of infants born weighing less than 1500 g.
  • mortality rate of 15-30%
  • usually occurs in the second week of life after the initiation of enteral feeds
  • pathogenesis is multifactorial
  • appears to involve an overreactive response of the immune system to an insult.
  • increased intestinal permeability, bacterial translocation, and sepsis.

Adult

Adult gastrointestinal tract cartoon02.jpg Adult gastrointestinal tract cartoon01.jpg
Gastrointestinal Tract Terms  
  • allantois - An extraembryonic membrane, endoderm in origin extension from the early hindgut, then cloaca into the connecting stalk of placental animals, connected to the superior end of developing bladder. In reptiles and birds, acts as a reservoir for wastes and mediates gas exchange. In mammals is associated/incorporated with connecting stalk/placental cord fetal-maternal interface.
  • amnion - An extra-embryonic membrane, ectoderm and extraembryonic mesoderm in origin, also forms the innermost fetal membrane, that produces amniotic fluid. This fluid-filled sac initially lies above the trilaminar embryonic disc and with embryoic disc folding this sac is drawn ventrally to enclose (cover) the entire embryo, then fetus. The presence of this membane led to the description of reptiles, bird, and mammals as amniotes.
  • amniotic fluid - The fluid that fills amniotic cavity totally encloses and cushions the embryo. Amniotic fluid enters both the gastrointestinal and respiratory tract following rupture of the buccopharyngeal membrane. The late fetus swallows amniotic fluid.
  • buccal - (Latin, bucca = cheek) A term used to relate to the mouth (oral cavity).
  • bile salts - Liver synthesized compounds derived from cholesterol that function postnatally in the small intestine to solubilize and absorb lipids, vitamins, and proteins. These compounds act as water-soluble amphipathic detergents.
  • buccopharyngeal membrane - (oral membrane) (Latin, bucca = cheek) A membrane which forms the external upper membrane limit (cranial end) of the early gastrointestinal tract (GIT). This membrane develops during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane lies at the floor of the ventral depression (stomodeum) where the oral cavity will open and will breakdown to form the initial "oral opening" of the gastrointestinal tract. The equivilent membrane at the lower end of the gastrointestinal tract is the cloacal membrane.
  • cloacal membrane - Forms the external lower membrane limit (caudal end) of the early gastrointestinal tract (GIT). This membrane is formed during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane breaks down to form the initial "anal opening" of the gastrointestinal tract.
  • cholangiocytes - epithelial cells that line the intra- and extrahepatic ducts of the biliary tree. These cells modify the hepatocyte-derived bile, and are regulated by hormones, peptides, nucleotides, neurotransmitters, and other molecules.
  • coelom - Term used to describe a space. There are extraembryonic and intraembryonic coeloms that form during vertebrate development. The single intraembryonic coelom will form the 3 major body cavities: pleural, pericardial and peritoneal.
  • crypt of Lieberkühn - (intestinal gland, intestinal crypt) intestinal villi epithelia extend down into the lamina propria where they form crypts that are the source of epithelial stem cells and immune function.
  • foregut - The first of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract. The foregut runs from the buccopharyngeal membrane to the midgut and forms all the tract (esophagus and stomach) from the oral cavity to beneath the stomach. In addition, a ventral bifurcation of the foregut will also form the respiratory tract epithelium.
  • galactosemia - Metabolic abnormality where the simple sugar galactose (half of lactose, the sugar in milk) cannot be metabolised. People with galactosemia cannot tolerate any form of milk (human or animal). Detected by the Guthrie test.
  • gastrula - (Greek, gastrula = little stomach) A stage of an animal embryo in which the three germ layers (Endoderm/ Mesoderm/Ectoderm) have just formed.
  • gastrulation - The process of differentiation forming a gastrula. Term means literally means "to form a gut" but is more in development, as this process converts the bilaminar embryo (epiblast/hypoblast) into the trilaminar embryo (Endoderm/ Mesoderm/Ectoderm) establishing the 3 germ layers that will form all the future tissues of the entire embryo. This process also establishes the the initial body axes. (More? Gastrulation)
  • Guthrie test - (heel prick) A neonatal blood screening test developed by Dr Robert Guthrie (1916-95) for determining a range of metabolic disorders and infections in the neonate. (More? Guthrie test)
  • hindgut - The last of the three part/division foregut - midgut - hindgut) of the early forming gastrointestinal tract. The hindgut forms all the tract from the distral transverse colon to the cloacal membrane and extends into the connecting stalk (placental cord) as the allantois. In addition, a ventral of the hindgut will also form the urinary tract (bladder, urethra) epithelium.
  • intraembryonic coelom - The "horseshoe-shaped" space (cavity) that forms initially in the third week of development in the lateral plate mesoderm that will eventually form the 3 main body cavities: pericardial, pleural, peritoneal. The intraembryonic coelom communicates transiently with the extraembryonic coelom.
  • neuralation - The general term used to describe the early formation of the nervous system. It is often used to describe the early events of differentiation of the central ectoderm region to form the neural plate, then neural groove, then neural tube. The nervous system includes the central nervous system (brain and spinal cord) from the neural tube and the peripheral nervous system (peripheral sensory and sympathetic ganglia) from neural crest. In humans, early neuralation begins in week 3 and continues through week 4.
  • neural crest - region of cells at the edge of the neural plate that migrates throughout the embryo and contributes to many different tissues. In the gastrointestinal tract it contributes mainly the enteric nervous system within the wall of the gut responsible for peristalsis and secretion.
  • pharynx - uppermost end of gastrointestinal and respiratory tract, in the embryo beginning at the buccopharyngeal membrane and forms a major arched cavity within the phrayngeal arches.
  • somitogenesis The process of segmentation of the paraxial mesoderm within the trilaminar embryo body to form pairs of somites, or balls of mesoderm. A somite is added either side of the notochord (axial mesoderm) to form a somite pair. The segmentation does not occur in the head region, and begins cranially (head end) and extends caudally (tailward) adding a somite pair at regular time intervals. The process is sequential and therefore used to stage the age of many different species embryos based upon the number visible somite pairs. In humans, the first somite pair appears at day 20 and adds caudally at 1 somite pair/4 hours (mouse 1 pair/90 min) until on average 44 pairs eventually form.
  • splanchnic mesoderm - Gastrointestinal tract (endoderm) associated mesoderm formed by the separation of the lateral plate mesoderm into two separate components by a cavity, the intraembryonic coelom. Splanchnic mesoderm is the embryonic origin of the gastrointestinal tract connective tissue, smooth muscle, blood vessels and contribute to organ development (pancreas, spleen, liver). The intraembryonic coelom will form the three major body cavities including the space surrounding the gut, the peritoneal cavity. The other half of the lateral plate mesoderm (somatic mesoderm) is associated with the ectoderm of the body wall.
  • stomodeum - (stomadeum, stomatodeum) A ventral surface depression on the early embryo head surrounding the buccopharyngeal membrane, which lies at the floor of this depression. This surface depression lies between the maxillary and mandibular components of the first pharyngeal arch.
Other Terms Lists  
Terms Lists: ART | Birth | Bone | Cardiovascular | Cell Division | Gastrointestinal | Genetic | Hearing | Heart | Immune | Integumentary | Neural | Oocyte | Palate | Placenta | Renal | Respiratory | Spermatozoa | Ultrasound | Vision | Historic | Glossary

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.


References

  1. 1.0 1.1 A S Goldman Modulation of the gastrointestinal tract of infants by human milk. Interfaces and interactions. An evolutionary perspective. J. Nutr.: 2000, 130(2S Suppl);426S-431S PubMed 10721920 | PDF


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Cite this page: Hill, M.A. 2017 Embryology BGDB Gastrointestinal - Postnatal. Retrieved September 26, 2017, from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Gastrointestinal_-_Postnatal

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© Dr Mark Hill 2017, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G