Gastrointestinal Tract - Intestine Development: Difference between revisions
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Small intestine tertiary loops week 8. <ref name=PMID26297675><pubmed>26297675</pubmed></ref> | |||
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Revision as of 13:09, 24 January 2017
Embryology - 26 Jun 2024 Expand to Translate |
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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
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More recent papers |
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This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Intestine Embryology <pubmed limit=5>Intestine Embryology</pubmed> |
Adult Small Intestine
Duodenum | Jejunum and ileum |
- Duodenum (adult 25 cm length)
- Jejunum (adult 1.4 m length)
- Ileum (adult 3.5 m length)
The adult ileum contains specialised aggregated lymphoid nodules known as Peyer's patches.
Adult jejunum histology | Adult ileum Peyer's patches |
See small intestine or bowel length (see also Fetal Intestine Length and Small Intestine 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
Colour code:
|
Week 7
Human embryo small intestine secondary loops (week 7 to 8).[5]
Week 8
|
Late embryonic small intestine commencing at the duodenum, continuing as ventrally herniated and returning to join the colon.
Small intestine tertiary loops week 8. [5]
- Links: Carnegie stage 22 | Week 8
Rotation
Normal intestinal rotation[6]
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.[9]
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.[9]
Appendix
The appendix (vermiform appendix, vermix) is a finger-like diverticulum located anatomically at the cecum, the junction between the small and large intestines (colon). The length (2.5-13 cm) is longer in both infants and children and also has more abundant lymphatic tissue in early life. The wall structure is similar to the small intestine (though with no villi), nor plicae circularis. Its immune function is associated with the many lymph nodules surrounding the lumen that extend from the mucosa into the submucosa. It has also been suggested as a repository for beneficial intestinal microflora. See also the review comparing the appendix in different species.[10]
There appears to be a developmental anatomical differences in the fetal position of the appendix in males and females.[11] In the fetus, lymphocyte aggregates first appear in this region during the second trimester, week 15 (GA week 17).[12]
Historically, Berengario da Carpi (1460-c.1530) in Commentaria cum amplissimis additionibus super Anatomia Mundini (1521) was the first to describe the human appendix.
Hindgut
Anatomically the distal third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and rectum. The developmental timing of the anus and rectum formation[13] in human embryos of the Carnegie Collection has been previously carried out (1974). A more recent study[14] has also been made of the Kyoto Collection embryos.
There has been some recent controversy over the "anal membrane" formation.
A recent study hindgut and anorectum development in human embryos shows that Wnt5a is active in this region prior to anus formation, when it is down-regulated.[15]
Other studies - PMID 19496155 PMID 10504783 PMID 9562679 PMID 9243909 PMID 21708335 (rat)
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.[16]
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 26) 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[17] and a later modified by Wallbridge in 1963[18], subsequently two more types of appendix abnormalities have been identified.[19][20]
Modified Cave-Wallbridge Classification (table from[21])
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 |
Short Bowel Syndrome
Short bowel syndrome (SBS) results typically due to developmental abnormalities, extensive intestinal resection during the neonatal period, or necrotising enterolitis.[22]
- reduces gut function for digestion and absorption of nutrients (intestinal failure).
- Links: PubMed Health | Better Health
Molecular Factors
- Cdx (Caudal-type homeobox) group of ParaHox genes (mouse Cdx1, Cdx2 and Cdx4)[23]
- FGF9
References
- ↑ 1.0 1.1 <pubmed>22253716</pubmed>
- ↑ <pubmed>26995337</pubmed>
- ↑ <pubmed>24496613</pubmed>| Development
- ↑ <pubmed>18653563</pubmed>
- ↑ 5.0 5.1 <pubmed>26297675</pubmed>
- ↑ <pubmed>20549505</pubmed>| PMC2908440
- ↑ <pubmed>3244599</pubmed>
- ↑ <pubmed>16891202</pubmed>
- ↑ 9.0 9.1 <pubmed>1752463</pubmed>| PMC1379160 | Gut.
- ↑ <pubmed>11135184</pubmed>
- ↑ <pubmed>11316934</pubmed>
- ↑ <pubmed>15173960</pubmed>
- ↑ de Vries PA. and Friedland GW. The staged sequential development of the anus and rectum in human embryos and fetuses. (1974) J. Pediatr. Surg., 9(5): 755-69 PMID 4424274
- ↑ <pubmed>23480355</pubmed>
- ↑ <pubmed>21431850</pubmed>
- ↑ <pubmed>19782301</pubmed>
- ↑ <pubmed>17104589</pubmed>
- ↑ <pubmed>13998581</pubmed>
- ↑ <pubmed>2772830</pubmed>
- ↑ <pubmed>5635427</pubmed>
- ↑ <pubmed>21513538</pubmed>| J Medical Case Reports | PDF
- ↑ <pubmed>3159212</pubmed>
- ↑ <pubmed>20298182</pubmed>
Reviews
<pubmed></pubmed> <pubmed> 24496613</pubmed> <pubmed>21978911</pubmed> <pubmed>19782301</pubmed>
Articles
<pubmed>26297675</pubmed> <pubmed>26599074</pubmed> <pubmed>21750033</pubmed> <pubmed>14745932</pubmed>
Search Pubmed
Search Bookshelf Intestine Development
Search Pubmed Now: Intestine Embryology | Intestine Development
Additional Images
Historic Images
Historic Disclaimer - information about historic embryology pages |
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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History | Historic Embryology Papers) |
Frazer JE. and Robbins RH. On the factors concerned in causing rotation of the intestine in man. (1915) J Anat. 50(1): 75-110. PMID 17233053
External Links
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- NIH PubMed Health Short Bowel Syndrome
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Cite this page: Hill, M.A. (2024, June 26) 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