BGDB Gastrointestinal - Fetal

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


Fetal Development

The Embryonic period involved transient structures to establish body and placental tissues, folding and form. The long human Fetal period (4x the embryonic period) is a time of extensive growth in size and mass as well as ongoing differentiation of organ systems established in the embryonic period. (More? See Fetal Notes)

As many students are new to embryology the majority of the practical class time has been spent introducing general concepts of early human development and combining this with the early formation of GIT structures. While the fetal period is substantially longer, there will be much less content to be covered.

Fetal developmental features include: the growth and rotation of intestines initially herniated outside the ventral body wall; changes in mesenteries; development of the blood supply and tract wall.

Finally consider the initial functions of the tract with amionic fluid swallowing and the accumulation of both secretions and swallowed components within the large intestine.

Early Fetus

Begin by just looking at the fetal anatomy in sections taken through the above 10 week female fetus (which is approximately 40 mm in size) and see how this compares with what you already know of adult GIT anatomy.


There are 4 sections taken in the parasagittal and sagittal plane (moving from the right at Plane A towards the midline at Plane D). Click on the small images (or the text below) to open the linked large image pages.

Midgut Herniation

Week 10

In the week 10 fetus (right) the midgut is still herniated (lying outside the ventral body wall) at the umbilicus. We saw in earlier pages that this heriation began back in the embryonic period (week 5) and the initial loop undergoes a series of rotations through embryonic and early fetal periods which position the midgut in its correct adult anatomical locations. These rotations are around the superior mesenteric artery (which supplies this region) and the associated mesentry. (Note this rotation is complicated and explained differently in different texts)

One week later (week 11) continued fetal body wall growth (and other factors) returns the midgut herniation returns to the abdominal cavity.

Bailey299 300.jpg Bailey304.jpg


Cartoon of Midgut Rotation
width=320px|height=265px|controller=true|autoplay=false</qt> View from left hand side of embryo facing left. Sequence spans approx 6-11 weeks of development.


There is an initial 90 degree rotation followed by 2 more 90 degree rotations to give 270 degrees total. The upper GIT is shader light green, the red vessel is the superior mesenteric artery off the dorsal aorta.

Stomach Mesentery

Greater-omentum.jpg

In the second trimester, the ventral and dorsal mesenteries associated with the stomach are still anatomically different from the newborn. The figure shows a lateral view of this process comparing the early second trimester arrangement with the newborn structure.

Ventral Mesogastrium

Attached to the superior end of the stomach will form the lesser omentum. This structure will connect the lesser curvature of the stomach to the liver as a ligamentous structure.

Dorsal Mesogastrium

Attached to the inferior end of the stomach initially as an extended fold, this later fuses as a single "apron-like" structure, the greater omentum. Fusion will also incorporate the transverse colon part of the large intestine.

This will also contribute the gastrosplenic ligament (gastrolienal ligament).

Blood Supply

GIT blood supply.jpg

Each region of the gastrointestinal tract has a specific arterial supply which historically defined the 3 gastrointestinal tract regions (foregut, midgut and hindgut).


  1. Foregut - celiac artery (Adult: pharynx, esophagus, stomach, upper duodenum, respiratory tract, liver, gallbladder pancreas)
  2. Midgut - superior mesenteric artery (Adult: lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, half transverse colon)
  3. Hindgut - inferior mesenteric artery (Adult: half transverse colon, descending colon, rectum, superior part anal canal)

Fetal Tract Development

Small intestine villi and crypts
Adult Peyer's patch

Week 11 - villi begin to appear in small intestine, goblet cells present

Week 16 - villi apparent in entire intestine

Adult small intestine will be divided into 3 regions with the same basic histological organization.

  1. duodenum (25-30 cm)
  2. jejunum (about first two-fifths of the rest)
  3. ileum

Week 20 - Peyer's patches appear in small intestine

The adult intestinal immune system includes:

  • Peyer's patches
  • isolated lymphoid follicles
  • cryptopatches - small clusters of lymphoid cells with an immature lymphocyte phenotype and dendritic cells.
  • mesenteric lymph nodes

Amniotic Fluid and Meconium

Amniotic Fluid Swallowing In early embryonic development both the buccopharyngeal and cloacal membranes degenerated, allowing the GIT to be filled with amniotic fluid. Towards the end of the fetal period the fetus is now swallowing approximately 500 ml of amniotic fluid / day.

This swallowed amniotic fluid moves through the GIT from esophagus, to stomach, to small intestine, stopping at the large bowel. In the large bowel the majority of fluid (water) is absorbed, along with electrolytes, glucose, urea and hormones. This process may contribute to fetal nutrition and prepare the GIT for its postnatal function. The process of swallowing amniotic fluid has been suggested to also help regulate fluid volume.

Polyhydramnios (or hydramnios) refers to abnormally high amniotic fluid levels. This can be caused by a range of different abnormalities: byesophageal atresia, duodenal atresia, anencephaly, hydrops fetalis, achondroplasia, Beckwith-Wiedemann syndrome, diaphragmatic hernia, gastroschisis, multiple gestations (twins or triplets) or gestational diabetes.

Fetal Meconium (green fecal material) is the mixture of substances (debris, glandular secretions, fatty material and bile pigments) that accumulate in the large bowel. The mixture will form the neonatal meconium which is the first (usually within 24h to 48h) postnatal excretion from the GIT. If no discharge (bowel motion) is observed in this period it can be indicative of an abnormality of the GIT.

Meconium Aspiration can occur near term or at delivery, if meconiumis discharged into the amiotic fluid (meconium stained amniotic fluid) and then injested by the fetus as it swallows amiotic fluid. This can then lead to meconium aspiration syndrome (MAS), meconium drawn into the fetal/newborn lungs, causing inflammation, cell death and potentially perinatal death.


BGDsmall.jpg
Practical 1: Trilaminar Embryo | Early Embryo | Late Embryo | Fetal | Postnatal | Abnormalities | Lecture | Quiz




BGDsmall.jpg

BGDB: Lecture - Gastrointestinal System | Practical - Gastrointestinal System | Lecture - Face and Ear | Practical - Face and Ear | Lecture - Endocrine | Lecture - Sexual Differentiation | Practical - Sexual Differentiation | Tutorial


Glossary Links

Glossary: A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | Numbers | Symbols | Term Link



Cite this page: Hill, M.A. (2024, March 28) Embryology BGDB Gastrointestinal - Fetal. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/BGDB_Gastrointestinal_-_Fetal

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