Gastrointestinal Tract - Intestine Development
Introduction
The part of the gastrointestinal tract (GIT) lying between the stomach and anus, is described as the intestines or bowel. This region is further divided anatomically and functionally into the small intestine or bowel (duodenum, jejunum and ileum) and large intestine or bowel (cecum and colon). Initially development concerns the midgut region, connected to the yolk sac, and the hindgut region, ending at the cloacal membrane. This is followed by two mechanical processes of elongation and rotation. Elongation, growth in length, leaves the midgut "herniated" at the umbilicus and external to the abdomen. Rotation, around a mesentery axis, establishes the anatomical position of the large intestine within the peritoneal space.
Migration of neural crest cells into the wall establishes the enteric nervous system, which has a role in peristalsis and secretion. Prenatally, secretions also accumulate in this region and are the first postnatal bowel movement, the meconium.
The small intestine grows in length rapidly in the last trimester, at birth it is about half the eventual adult length (More? Small Intestine Length). Like most of the gut, this region is not "functional" until after birth, when development continues by populating the large intestine with commensal bacteria and the establishment of the immune structure in the wall.
Some Recent Findings
|
Adult Intestine
Intestinal Regions
Small intestine or bowel
- Duodenum (adult 25 cm length)
- Jejunum (adult 1.4 m length)
- Ileum (adult 3.5 m length)
Large intestine or bowel
- Cecum (caecum)
- Vermiform appendix ("appendix", adult 2 to 20 cm length)
- Colon
- Ascending colon (adult 25 cm length)
- Transverse colon
- Descending colon
- Sigmoid colon
Intestinal Functions
Small Intestine
- absorption of nutrients and minerals found in food
- Duodenum -principal site for iron absorption
Cecum
- connects the ileum with the ascending colon
- separated by the ileocecal valve (ICV, Bauhin's valve)
- connected to the vermiform appendix ("appendix")
Colon
- absorbs fluid, water and salts, from solid wastes
- site of commensal bacteria (flora) fermentation of unabsorbed material
Embryonic Development
Week 4
Quicktime | Flash |
Week 8
Quicktime | Flash |
Late embryonic small intestine commencing at the duodenum, continuing as ventrally herniated and returning to join the colon.
- Links: Carnegie stage 22 | Week 8
Rotation
Normal intestinal rotation[2]
Fetal Intestine Length
Fetal small Intestine length growth | Fetal Large Intestine length growth |
Small Intestine Length
Small intestine growth in length is initially linear (first half pregnancy to 32 cm CRL), followed by rapid growth in the last 15 weeks doubling the overall length. Growth continues postnatally but after 1 year slows again to a linear increase to adulthood.[5]
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.[5]
Intestinal Motility
The enteric nervous system neural crest-derived neurons interacts with the circular and longitudinal smooth muscle layers and the interstitial cells of Cajal to generate motility. The developmental timing data shown below is from a recent review.[6]
Neural Crest
week 5 - migrating neural crest cells reach the midgut
week 7 - neural crest cells have colonized the entire gut
- colonization occurs in a rostro-caudal sequence
Myenteric plexus (Auerbach's plexus, named after Leopold Auerbach (1828–1897) a German anatomist and neuropathologist.)
- is first formed plexus
- lies between the outer longitudinal and inner circular layers of muscularis externa
- provides motor innervation to both layers
- secretomotor innervation to the mucosa
- has both parasympathetic and sympathetic input
Submucosal Plexus (Meissner's plexus, named after Georg Meissner (1829–1905) a German anatomist and physiologist.)
- forms 2-3 days after the myenteric plexus
- formed by cells migrating from the myenteric plexus
- innervates smooth muscle of the muscularis mucosae
- has only parasympathetic fibers
Smooth Muscle
week 8 - esophagus circular muscle
week 11 - hindgut circular muscle
week 14 - hindgut concentric muscularis mucosae, circular muscle, and longitudinal muscle
Interstitial Cells of Cajal
Interstitial cells of Cajal (ICC) are electrical pacemaker cells within the gastrointestinal tract smooth muscle. They create the basal (slow waves) rhythm required for contraction and peristalsis. They are mesodermal in origin.
weeks 7-9 - cells initially appear
week 11 - distinct clusters
week 12-14 - clustered around myenteric ganglia along the entire gut
- Links: Neural Crest Development
Abnormalities
- Abnormality Links: Gastrointestinal Tract - Abnormalities | Intestine Development | Gastrointestinal Tract
- Lumen Abnormalities: Image - Duplication sites | Pyloric atresia | Jejunal atresia
- Rotation: Image - Midgut volvulus | Image - Intestinal malrotation | Image - Cecal volvulus | Image - Sigmoid volvulus | Ladd's band
- Meckel's Diverticulum: Meckel's Image 1 | Meckel's Image 2 | Meckel's Image 3 |
- Intestinal Aganglionosis: Image - Ostomy | Image - Stoma | Surgery 1 | Surgery 2 | Surgery 3
Cite this page: Hill, M.A. (2024, June 14) Embryology Gastrointestinal Tract - Intestine Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Gastrointestinal_Tract_-_Intestine_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
Appendix Duplication
Appendix duplication is an extremely rare congenital anomaly (0.004% to 0.009% of appendectomy specimens) first classified according to their anatomic location by Cave in 1936[7] and a later modified by Wallbridge in 1963[8], subsequently two more types of appendix abnormalities have been identified.[9][10]
Modified Cave-Wallbridge Classification (table from[11])
Classification of types of appendix duplication |
Features |
A | Single cecum with various degrees of incomplete duplication |
B1 (bird type) | Two appendixes symmetrically placed on either side of the ileocecal valve |
B2 (tenia coli type) | ne appendix arises from the cecum at the usual site, and the second
appendix branches from the cecum along the lines of the tenia at various distances from the first |
B3 | One appendix arises from the usual site, and the second appendix arises from
the hepatic flexura |
B4 | One appendix arises from the usual site, and the second appendix arises from
the splenic flexura |
C | Double cecum, each with an appendix |
Horseshoe appendix | One appendix has two openings into a common cecum |
Triple appendix | One appendix arises from the cecum at the usual site, and two additional appendixes arise from the colon |
Molecular Factors
- Cdx (Caudal-type homeobox) group of ParaHox genes (mouse Cdx1, Cdx2 and Cdx4)[12]
- FGF9
References
- ↑ <pubmed>18653563</pubmed>
- ↑ <pubmed>20549505</pubmed>| PMC2908440
- ↑ <pubmed>3244599</pubmed>
- ↑ <pubmed>16891202</pubmed>
- ↑ 5.0 5.1 <pubmed>1752463</pubmed>| PMC1379160 | Gut.
- ↑ <pubmed>19782301</pubmed>
- ↑ <pubmed>17104589</pubmed>
- ↑ <pubmed>13998581</pubmed>
- ↑ <pubmed>2772830</pubmed>
- ↑ <pubmed>5635427</pubmed>
- ↑ <pubmed>21513538</pubmed>| J Medical Case Reports | PDF
- ↑ <pubmed>20298182</pubmed>
Reviews
<pubmed>19782301</pubmed>
Articles
Search Pubmed
Search Bookshelf Intestine Development
Search Pubmed Now: Intestine Embryology | Intestine Development
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, June 14) Embryology Gastrointestinal Tract - Intestine Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Gastrointestinal_Tract_-_Intestine_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G