ANAT2341 Lab 5 - Postnatal

From Embryology
Lab 5: Introduction | Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Online Assessment


Birth leads to changes in many different systems. Within the context of this Practical class we will look briefly 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).

  • 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.
  • 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 Head Development Practical)


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

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 AS.[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


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.

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.

Links: PubMed Health - Necrotizing Enterocolitis


Gastrointestinal Tract

Adult gastrointestinal tract cartoon02.jpg Adult gastrointestinal tract cartoon01.jpg


Lung secondary lobule 01.jpg Lung primary lobule 01.jpg
Secondary Lung Lobule Primary Lung Lobule (longitudinal section)


  1. 1.0 1.1 <pubmed>10721920</pubmed>| PDF

Lab 5: Introduction | Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Online Assessment

ANAT2341 Course Timetable  
Week (Mon) Lecture 1 (Mon 1-2pm) Lecture 2 (Tue 3-4pm) Practical (Fri 1-3pm)
Week 2 (1 Aug) Introduction Fertilization Lab 1
Week 3 (8 Aug) Week 1 and 2 Week 3 Lab 2
Week 4 (15 Aug) Mesoderm Ectoderm Lab 3
Week 5 (22 Aug) Early Vascular Placenta Lab 4
Week 6 (29 Aug) Gastrointestinal Respiratory Lab 5
Week 7 (5 Sep) Head Neural Crest Lab 6
Week 8 (12 Sep) Musculoskeletal Limb Development Lab 7
Week 9 (19 Sep) Renal Genital Lab 8
Mid-semester break
Week 10 (3 Oct) Public Holiday Stem Cells Lab 9
Week 11 (10 Oct) Integumentary Endocrine Lab 10
Week 12 (17 Oct) Heart Sensory Lab 11
Week 13 (24 Oct) Fetal Birth and Revision Lab 12

ANAT2341 2016: Moodle page | ECHO360 | Textbooks | Students 2016 | Projects 2016

ANAT2341Lectures - Textbook chapters  
Lecture (Timetable) Textbook - The Developing Human Textbook - Larsen's Human Embryology
Embryology Introduction Introduction to the Developing Human
Fertilization First Week of Human Development Gametogenesis, Fertilization, and First Week
Week 1 and 2 Second Week of Human Development Second Week: Becoming Bilaminar and Fully Implanting
Week 3 Third Week of Human Development Third Week: Becoming Trilaminar and Establishing Body Axes
Mesoderm Fourth to Eighth Weeks of Human Development Fourth Week: Forming the Embryo
Ectoderm Nervous System Development of the Central Nervous System
Early Vascular Cardiovascular System Development of the Vasculature
Placenta Placenta and Fetal Membranes Development of the Vasculature
Endoderm - GIT Alimentary System Development of the Gastrointestinal Tract
Respiratory Respiratory System Development of the Respiratory System and Body Cavities
Head Pharyngeal Apparatus, Face, and Neck Development of the Pharyngeal Apparatus and Face
Neural Crest Nervous System Development of the Peripheral Nervous System
Musculoskeletal Muscular System Development of the Musculoskeletal System
Limb Development of Limbs Development of the Limbs
Renal Urogenital System Development of the Urinary System
Genital Urogenital System Development of the Urinary System
Stem Cells
Integumentary Integumentary System Development of the Skin and Its Derivatives
Endocrine Covered through various chapters (see also alternate text), read head and neck, neural crest and renal chapters.
Endocrinology Textbook - Chapter Titles  
Nussey S. and Whitehead S. Endocrinology: An Integrated Approach (2001) Oxford: BIOS Scientific Publishers; ISBN-10: 1-85996-252-1.

Full Table of Contents

Heart Cardiovascular System Development of the Heart
Sensory Development of Eyes and Ears Development of the Eyes
Fetal Fetal Period Fetal Development and the Fetus as Patient
Birth and Revision
Additional Textbook Content - The following concepts also form part of the theory material covered throughout the course.
  1. Principles and Mechanisms of Morphogenesis and Dysmorphogenesis
  2. Common Signaling Pathways Used During Development
  3. Human Birth Defect

Glossary Links

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Cite this page: Hill, M.A. (2024, May 22) Embryology ANAT2341 Lab 5 - Postnatal. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G