Gastrointestinal Tract - Mesentery Development

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Early embryonic mesentery (pink)

The adult gastrointestinal tract (GIT) is attached along its length by a dorsal mesentery between the stomach (oesophagogastric) and anus (anorectal junctions) arising from from splanchnic mesoderm. This differentiates into a mesothelium, an epithelium derived from mesoderm. The majority of the ventral mesentery is developmentally lost at the level of the midgut and only the dorsal mesentery remains in the adult, through which blood vessels, nerves and lymph connects to the gastrointestinal wall.

Recently mouse mesentery has been used as a transplantation site for human intestinal organoid study.[1]

GIT Links: Introduction | Medicine Lecture | Science Lecture | endoderm | mouth | oesophagus | stomach | liver | gall bladder | Pancreas | intestine | mesentery | tongue | taste | enteric nervous system | Stage 13 | Stage 22 | gastrointestinal abnormalities | Movies | Postnatal | milk | tooth | salivary gland | BGD Lecture | BGD Practical | GIT Terms | Category:Gastrointestinal Tract
GIT Histology Links: Upper GIT | Salivary Gland | Smooth Muscle Histology | Liver | Gall Bladder | Pancreas | Colon | Histology Stains | Histology | GIT Development
Historic Embryology - Gastrointestinal Tract  
1878 Alimentary Canal | 1882 The Organs of the Inner Germ-Layer The Alimentary Tube with its Appended Organs | 1902 The Organs of Digestion | 1903 Submaxillary Gland | 1906 Liver | 1907 Development of the Digestive System | 1907 Atlas | 1907 23 Somite Embryo | 1908 Liver and Vascular | 1910 Mucous membrane Oesophagus to Small Intestine | 1910 Large intestine and Vermiform process | Intestine and Peritoneum - 1911 Part 1 | 1911 Part 2 | 1912 Part 3 | 1913 Part 5 | 1913 Part 6 | 1912 Digestive Tract | 1912 Stomach | 1914 Digestive Tract | 1914 Intestines | 1914 Rectum | 1915 Pharynx | 1915 Intestinal Rotation | 1917 Entodermal Canal | 1918 Anatomy | 1921 Alimentary Tube | 1932 Gall Bladder | 1939 Alimentary Canal Looping | 2008 Liver | 2016 GIT Notes | Historic Disclaimer
Human Embryo: 1908 13-14 Somite Embryo | 1921 Liver Suspensory Ligament | 1926 22 Somite Embryo | 1907 23 Somite Embryo | 1937 25 Somite Embryo | 1914 27 Somite Embryo | 1914 Week 7 Embryo
Animal Development: 1913 Chicken | 1951 Frog

Historic Embryology: 1912 Small Intestine | 1912 large Intestine | 1915 Intestinal Rotation

Some Recent Findings

Sagittal view of female abdominal cavity
Sagittal view of abdominal cavity[2]
  • The development of the dorsal mesentery in human embryos and fetuses[3] "The vertebrate intestine has a continuous dorsal mesentery between pharynx and anus that facilitates intestinal mobility. Based on width and fate the dorsal mesentery can be subdivided into that of the caudal foregut, midgut, and hindgut. The dorsal mesentery of stomach and duodenum is wide and topographically complex due to strong and asymmetric growth of the stomach. The associated formation of the lesser sac partitions the dorsal mesentery into the right-sided "caval fold" that serves as conduit for the inferior caval vein and the left-sided mesogastrium. The thin dorsal mesentery of the midgut originates between the base of the superior and inferior mesenteric arteries, and follows the transient increase in intestinal growth that results in small-intestinal looping, intestinal herniation and, subsequently, return. The following fixation of a large portion of the abdominal dorsal mesentery to the dorsal peritoneal wall by adhesion and fusion is only seen in primates and is often incomplete. Adhesion and fusion of mesothelial surfaces in the lesser pelvis results in the formation of the "mesorectum".
  • Digestive Tract in Human Embryos Between Carnegie Stages 11 and 13[4] "We selected 37 human embryos at Carnegie Stage (CS) 11-13 (28-33 days after fertilization) and three-dimensionally analyzed the morphology and positioning of the digestive tract and derived primordia in all samples, using images reconstructed from histological serial sections. The digestive tract was initially formed by a narrowing of the yolk sac, and then several derived primordia such as the pharynx, lung, stomach, liver, and dorsal pancreas primordia differentiated during 12 (21-29 somites) and CS13 (≥ 30 somites). The differentiation of four pairs of pharyngeal pouches was complete in all 13 embryos. The respiratory primordium was recognized in ≥ 26-somite embryos and it flattened and then branched at CS13. The trachea formed and then elongated in ≥ 35-somite embryos. The stomach adopted a spindle shape in all ≥ 34-somite embryos, and the liver bud was recognized in ≥ 27-somite embryos. The dorsal pancreas appeared as definitive buddings in all but three CS13 embryos, and around these buddings, the small intestine bent in ≥ 33-somite embryos. In ≥ 35-somite embryos, the small intestine rotated around the cranial-caudal axis and had begun to form a primitive intestinal loop, which led to umbilical herniation."
More recent papers  
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This table shows an automated computer PubMed search using the listed sub-heading term.

  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
  • References appear in this list based upon the date of the actual page viewing.

References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

Links: References | Discussion Page | Pubmed Most Recent | Journal Searches

Search term: Mesentery Embryology

Ai Xiao-Ming, Lu Jin-Jing, Ho Li-Chen, Han Lu-Lu, Yue Xiong, Zhang Hong-Hai, Yang Nian-Yin A huge completely isolated duplication cyst complicated by torsion and lined by 3 different mucosal epithelial components in an adult: A case report. Medicine (Baltimore): 2018, 97(44);e13005 PubMed 30383655

Kevin Gerard Byrnes, Kieran McDermott, John Calvin Coffey Development of mesenteric tissues. Semin. Cell Dev. Biol.: 2018; PubMed 30347243

Anke Vater, Johann Maierl Adaptive Anatomical Specialization of the Intestines of Alpacas Taking into Account their Original Habitat and Feeding Behaviour. Anat Rec (Hoboken): 2018; PubMed 30288956

Yan Peng, Li Min Jia, Bao Xin Li, Li Ping Xie, Zun Jiang Xie, Jin Hua Zheng Expression of Pref-1 and Related Chemokines during theDevelopment of Rat Mesenteric Lymph Nodes. Biomed. Environ. Sci.: 2018, 31(7);507-514 PubMed 30145985

Jill P J M Hikspoors, Nutmethee Kruepunga, Greet M C Mommen, Jean-Marie P W U Peeters, Cindy J M Hülsman, S Eleonore Köhler, Wouter H Lamers The development of the dorsal mesentery in human embryos and fetuses. Semin. Cell Dev. Biol.: 2018; PubMed 30142441

Older papers  
These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.

See also the Discussion Page for other references listed by year and References on this current page.

  • Growth of the colon and rectum throughout gestation: evaluation with fetal MRI[5] "Congenital abnormalities of the gastrointestinal tract are increasingly being evaluated by prenatal magnetic resonance imaging (MRI). However, there is a paucity of reports describing the normal quantitative development of the fetal colon and rectum on MRI. This study provides normal ranges of the prenatal colon and rectum as a function of gestational age. They may serve as reference values when interpreting fetal MRI."
  • Review - How to make an intestine[6] With the high prevalence of gastrointestinal disorders, there is great interest in establishing in vitro models of human intestinal disease and in developing drug-screening platforms that more accurately represent the complex physiology of the intestine. We will review how recent advances in developmental and stem cell biology have made it possible to generate complex, three-dimensional, human intestinal tissues in vitro through directed differentiation of human pluripotent stem cells.


Greater omentum 001 icon.jpg
 ‎‎Greater Omentum
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Lesser sac 01 icon.jpg
 ‎‎Lesser sac
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The following are anatomical sub-regions of the continuous mesentery.

  • dorsal mesogastrium
  • mesoduodenum
  • mesenteric root region
  • small intestine region
  • right mesocolon
  • left mesocolon
  • mesosigmoid
  • mesorectum

Small Intestine

Intestinal Functions

Small Intestine

  • absorption of nutrients and minerals found in food
  • Duodenum -principal site for iron absorption


  • absorbs fluid, water and salts, from solid wastes

Embryonic Development

Week 4


Colour code:

  • Foregut - oropharyngeal membrane, oesophagus, pharynx (dark salmon - Foregut, oropharyngeal membrane, oesophagus, pharynx)
  • Trachea and Lung Buds (dark blue - Trachea and Lung Buds)
  • Mesonephros (yellow - mesonephros)
  • Mesonephric Ducts (light blue - mesonephric ducts)
  • Hindgut and Cloaca (brown - hindgut and cloaca)
 ‎‎GIT Stage 13
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Week 7

Small intestine secondary loops week 7 to 8

Human embryo small intestine secondary loops (week 7 to 8).[7]

Week 8

 ‎‎GIT Stage 22
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Stage 22 image 088.jpg Stage 22 image 089.jpg

Late embryonic small intestine commencing at the duodenum, continuing as ventrally herniated and returning to join the colon.

Small intestine tertiary loops week 8

Small intestine tertiary loops week 8.[7]

Links: Carnegie stage 22 | Week 8


A recent 3 dimensional study[7] has suggested a modified “en-bloc rotation” of the small intestine, compared the the earlier simplified description of 270 degree rotation.

Fetal Intestine Length

Fetal small Intestine length growth graph.jpg Fetal large Intestine length growth graph.jpg
Fetal small Intestine length growth Fetal Large Intestine length growth

Data from[8][9]

Fetal rectum growth graph.jpg

Data from[5]

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.[10]

Small Intestine Length
Age (weeks GA 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.[10]


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[11] in human embryos of the Carnegie Collection has been previously carried out (1974). A more recent study[12] 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.[13]

Other studies - [14][15][16][17][18] (rat)


Intestinal malrotation[19]

Midgut Volvulus[20]

Molecular Factors


The adult mesentery consists of loose irregular connective tissue, areolar connective tissue, collagen fibres, elastic fibres. There are also numerous mast cells (granulocytes) containing histamine and other substances released during inflammatory and allergic reactions.

Adult Mesentery Histology
Low power (x10) High power (x40)
Mesentery histology 02.jpg Mesentery histology 01.jpg


  1. Cortez AR, Poling HM, Brown NE, Singh A, Mahe MM & Helmrath MA. (2018). Transplantation of human intestinal organoids into the mouse mesentery: A more physiologic and anatomic engraftment site. Surgery , 164, 643-650. PMID: 30072255 DOI.
  2. Isaza-Restrepo A, Martin-Saavedra JS, Velez-Leal JL, Vargas-Barato F & Riveros-Dueñas R. (2018). The Peritoneum: Beyond the Tissue - A Review. Front Physiol , 9, 738. PMID: 29962968 DOI.
  3. Hikspoors JPJM, Kruepunga N, Mommen GMC, Peeters JPWU, Hülsman CJM, Eleonore Köhler S & Lamers WH. (2018). The development of the dorsal mesentery in human embryos and fetuses. Semin. Cell Dev. Biol. , , . PMID: 30142441 DOI.
  4. Ueno S, Yamada S, Uwabe C, Männer J, Shiraki N & Takakuwa T. (2016). The Digestive Tract and Derived Primordia Differentiate by Following a Precise Timeline in Human Embryos Between Carnegie Stages 11 and 13. Anat Rec (Hoboken) , 299, 439-49. PMID: 26995337 DOI.
  5. 5.0 5.1 Ben-Nun MS, Ben-Shlush A & Raviv Zilka L. (2018). Growth of the colon and rectum throughout gestation: evaluation with fetal MRI. Acta Radiol Open , 7, 2058460118761206. PMID: 29531795 DOI.
  6. Wells JM & Spence JR. (2014). How to make an intestine. Development , 141, 752-60. PMID: 24496613 DOI.
  7. 7.0 7.1 7.2 Soffers JH, Hikspoors JP, Mekonen HK, Koehler SE & Lamers WH. (2015). The growth pattern of the human intestine and its mesentery. BMC Dev. Biol. , 15, 31. PMID: 26297675 DOI.
  8. FitzSimmons J, Chinn A & Shepard TH. (1988). Normal length of the human fetal gastrointestinal tract. Pediatr Pathol , 8, 633-41. PMID: 3244599
  9. Archie JG, Collins JS & Lebel RR. (2006). Quantitative standards for fetal and neonatal autopsy. Am. J. Clin. Pathol. , 126, 256-65. PMID: 16891202 DOI.
  10. 10.0 10.1 Weaver LT, Austin S & Cole TJ. (1991). Small intestinal length: a factor essential for gut adaptation. Gut , 32, 1321-3. PMID: 1752463
  11. 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
  12. Hashimoto R. (2013). Development of the human tail bud and splanchnic mesenchyme. Congenit Anom (Kyoto) , 53, 27-33. PMID: 23480355 DOI.
  13. Li FF, Zhang T, Bai YZ, Yuan ZW & Wang WL. (2011). Spatiotemporal expression of Wnt5a during the development of the hindgut and anorectum in human embryos. Int J Colorectal Dis , 26, 983-8. PMID: 21431850 DOI.
  14. van der Putte SC. (2009). The development of the human anorectum. Anat Rec (Hoboken) , 292, 951-4. PMID: 19496155 DOI.
  15. Kromer P. (1999). Further study of the urorectal septum in staged human embryos. Folia Morphol. (Warsz) , 58, 53-63. PMID: 10504783
  16. Nievelstein RA, van der Werff JF, Verbeek FJ, Valk J & Vermeij-Keers C. (1998). Normal and abnormal embryonic development of the anorectum in human embryos. Teratology , 57, 70-8. PMID: 9562679 <70::AID-TERA5>3.0.CO;2-A DOI.
  17. Kromer P. (1996). Development of the urorectal septum and differentiation of the urogenital sinus in human embryos of stages 13 to 19. Folia Morphol. (Warsz) , 55, 362-3. PMID: 9243909
  18. Kluth D, Fiegel HC & Metzger R. (2011). Embryology of the hindgut. Semin. Pediatr. Surg. , 20, 152-60. PMID: 21708335 DOI.
  19. Ezer SS, Oguzkurt P, Temiz A, Ince E, Gezer HO, Demir S & Hicsonmez A. (2016). Intestinal malrotation needs immediate consideration and investigation. Pediatr Int , 58, 1200-1204. PMID: 27353636 DOI.
  20. Coste AH & Bhimji SS. (2018). Midgut Volvulus. , , . PMID: 28722991


Byrnes KG, McDermott K & Coffey JC. (2018). Development of mesenteric tissues. Semin. Cell Dev. Biol. , , . PMID: 30347243 DOI.

Byrnes KG, Walsh D, Dockery P, McDermott K & Coffey JC. (2018). Anatomy of the mesentery: Current understanding and mechanisms of attachment. Semin. Cell Dev. Biol. , , . PMID: 30316831 DOI.

Isaza-Restrepo A, Martin-Saavedra JS, Velez-Leal JL, Vargas-Barato F & Riveros-Dueñas R. (2018). The Peritoneum: Beyond the Tissue - A Review. Front Physiol , 9, 738. PMID: 29962968 DOI.

Wells JM & Spence JR. (2014). How to make an intestine. Development , 141, 752-60. PMID: 24496613 DOI.

Noah TK, Donahue B & Shroyer NF. (2011). Intestinal development and differentiation. Exp. Cell Res. , 317, 2702-10. PMID: 21978911 DOI.

Burns AJ, Roberts RR, Bornstein JC & Young HM. (2009). Development of the enteric nervous system and its role in intestinal motility during fetal and early postnatal stages. Semin. Pediatr. Surg. , 18, 196-205. PMID: 19782301 DOI.


Wozniak S, Florjanski J, Kordecki H, Podhorska-Okolow M & Domagala Z. (2018). Fetal sigmoid colon mesentery - In relevance in fetal ultrasound application. A pilot study. Ann. Anat. , 216, 152-158. PMID: 29292173 DOI.

Cho BH, Kim JH, Jin ZW, Wilting J, Rodríguez-Vázquez JF & Murakami G. (2018). Topographical anatomy of the intestines during in utero physiological herniation. Clin Anat , 31, 583-592. PMID: 29044646 DOI.

Nerurkar NL, Mahadevan L & Tabin CJ. (2017). BMP signaling controls buckling forces to modulate looping morphogenesis of the gut. Proc. Natl. Acad. Sci. U.S.A. , 114, 2277-2282. PMID: 28193855 DOI.

Soffers JH, Hikspoors JP, Mekonen HK, Koehler SE & Lamers WH. (2015). The growth pattern of the human intestine and its mesentery. BMC Dev. Biol. , 15, 31. PMID: 26297675 DOI.

Coffey JC, Culligan K, Walsh LG, Sehgal R, Dunne C, McGrath D, Walsh D, Moore M, Staunton M, Scanlon T, Dewhurst C, Kenny B, O'Riordan C, O'Brien JM, Quondamatteo F & Dockery P. (2016). An appraisal of the computed axial tomographic appearance of the human mesentery based on mesenteric contiguity from the duodenojejunal flexure to the mesorectal level. Eur Radiol , 26, 714-21. PMID: 26186959 DOI.

Davis NM, Kurpios NA, Sun X, Gros J, Martin JF & Tabin CJ. (2008). The chirality of gut rotation derives from left-right asymmetric changes in the architecture of the dorsal mesentery. Dev. Cell , 15, 134-45. PMID: 18606147 DOI.

Cascio S, Tien AS, Agarwal P & Tan HL. (2006). Dorsal mesenteric agenesis without small bowel atresia: a rare cause of midgut volvulus in children. J. Pediatr. Surg. , 41, E5-7. PMID: 16952580 DOI.

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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. liver
  • 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. liver
  • 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.
  • mesothelium - The mesoderm derived epithelial covering of coelomic organs and also line their cavities.
  • 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.
  • peritoneal stomata - the main openings forming the pathways for drainage of intra-peritoneal fluid from the peritoneal cavity into the lymphatic system.
  • 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.
  • recanalization - describes the process of a hollow structure becoming solid, then becoming hollow again. For example, this process occurs during GIT, auditory and renal system development.
  • 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  
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Frazer JE. and Robbins RH. On the factors concerned in causing rotation of the intestine in man. (1915) J Anat Physiol. 50(1): 75-110. PMID 17233053

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