This current page contains GIT Practical will link to information about GIT organ development. You do not need this information to complete the Practical class.
Arises at embryonic junction (septum transversum): externally is where ectoderm of amnion meets endoderm of yolk sac and internally is where the foregut meets the midgut
Mesenchymal structure of transverse septum provides a support within which both blood vessels and liver begin to form.
The transverse septum (septum transversum) arises at an embryonic junctional site. The junctional region externally is where the ectoderm of the amnion meets the endoderm of the yolk sac. The junctional region internally is where the foregut meets the midgut. The mesenchymal structure of the transverse septum provides a support within which both blood vessels and the liver begin to form. This structure grows rapidly.
The transverse septum then differentiates to form the hepatic diverticulum and the hepatic primordium, these two structures together will go on to form different components of the mature liver and gall bladder.
The rapidly developing liver forms a visible surface bulge on the embryo directly under the heart bulge.
Liver Bud
Differentiates to form the hepatic diverticulum and hepatic primordium, generates the gall bladder then divides into right and left hepatic buds.
Three connecting stalks (cystic duct, hepatic ducts) which fuse to form bile duct.
Hepatic Bud
Left Hepatic Bud- left lobe, quadrate, caudate (both q and c anatomically Left)
Right Hepatic Bud- right lobe
Function - Haemopoiesis
Embryonic liver also involved in blood formation, after the yolk sac and blood islands acting as a primary site.
Liver Structural Origins
Hepatic Buds- form hepatocytes, produce bile from week 13 (forms meconium of newborn)
Vitelline Veins- form sinusoids
Mesenchyme- form connective tissue and Kupffer cells
(More? GIT Notes - Liver Development)
Embryo (stage 13/14) showing gall bladder and liver
The hepatic diverticulum divides into two parts: pars hepatica (larger cranial part, primordium of the liver) and pars cystica (smaller ventral invagination, primordium of gall bladder).
The pars cystica vacuolates and expands, the stalk becoming the cystic duct. This structure is initially hollow, then solid (by proliferation of epithelial lining), and then recanalized occurs by vacuolation of this expanded epithelium. (some text above modified from Bani-Hani KE., 2005)
Embryo (stage 22) showing gall bladder and liver
(More? GIT Notes - Liver Development)
Spleen arises in week 5 within dorsal mesogastrium as proliferating mesenchyme.
Embryo (Stage 13) Dorsal Mesogastrium
Haematopoietic function (like the liver) cells arise from yolk sac wall. Spleen generates both red and white cells in the 2nd trimester. Note that embryonic RBCs remain nucleated.
(More? GIT Notes - Spleen Development)
At the foregut/midgut junction the septum transversum generates 2 pancreatic buds (dorsal and ventral endoderm) which will fuse to form the pancreas. The dorsal bud arises first and generates most of the pancreas. Differentiates to establish specific cells for endocrine and exocrine function.
Stage 22 Embryo Pancreas
In the fetal period islet cell clusters (icc) differentiate from pancratic bud endoderm. These cell clusters form acini and ducts (exocrine). On the edge of these cell clusters pancreatic islets (endocrine) also form.
The pancreas exocrine function begins after birth, while the endocrine function (hormone release) can be measured from 10 to 15 weeks onward. At this stage, it is not clear what the exact roles of these hormones are in regulating fetal growth. (MH - the pancreas will be covered again in Endocrine Lecture)
(More? GIT Notes - Pancreas Development)
After the stomach the initial portion of the GIT tube is the duodenum which initially lies in the midline within the peritoneal cavity, but then (along with the attached pancreas) undergoes rotation to become a retroperitoneal structure. (More? GIT Folding)
The diagram below shows this rotation with spinal cord at the top, vertebral body then dorsal aorta then pertioneal wall and cavity.
Rotation of the Duodenum
UNSW Embryology General Notes on Gastrointestinal Tract Development
Embryo Images by Drs. Kathleen K. Sulik and Peter R. Bream Jr. Seven linked notes/images sections on Gut Development
Developmental Biology. 6th ed. Gilbert, Scott F. Sunderland (MA): Sinauer Associates, Inc.; c2000
This textbook covers developmentnot only in humans but other species including plants. As such, some of the material will not be directly relevant to human development, but should be used comparatively or as a model.
The entire text and images is available free online from the NCBI Bookshelf. You can either click the provided links or do your own search using the search link.
Image: Figure 15.26. Formation of the human digestive system
Molecular Biology of the Cell 4th ed. Alberts, Bruce; Bray, Dennis; Lewis, Julian; Raff, Martin; Roberts, Keith; Watson, James D. New York and London: Garland Publishing; c2002. This is the Cell Biology "bible".
The entire text and images is available free online from the NCBI Bookshelf. You can either click the provided links or do your own search using the search link.
The Lining of the Small Intestine Renews Itself Faster Than Any Other Tissue
GIT References This page contains links to selected Gastrointestinal Tract references from National Library of Medicine PubMed and other sources. There are also links to pages on specific topics and a search window for entering your own term and carrying out a database search.
In general, these scientific review papers are in significantly more detail than you either require or understand at this stage. These papers do though give an overview/idea of our current understanding of GIT developmental mechanisms. No harm in having a look.......
Stainier DY. No organ left behind: tales of gut development and evolution. Science. 2005 Mar 25;307(5717):1902-4.
de Santa Barbara P, van den Brink GR, Roberts DJ. Development and differentiation of the intestinal epithelium. Cell Mol Life Sci. 2003 Jul;60(7):1322-32. Review.
Cleaver O, Krieg PA. Notochord patterning of the endoderm. Dev Biol. 2001 Jun 1;234(1):1-12. Review.
Roberts DJ. Molecular mechanisms of development of the gastrointestinal tract. Dev Dyn. 2000 Oct;219(2):109-20. Review.
Grapin-Botton A, Melton DA. Endoderm development: from patterning to organogenesis. Trends Genet. 2000 Mar;16(3):124-30. Review.
Montgomery RK, Mulberg AE, Grand RJ. Development of the human gastrointestinal tract: twenty years of progress. Gastroenterology. 1999 Mar;116(3):702-31. Review.
This database is probably a bit advanced to use at this stage, but as your knowledge grows, should be an ongoing invaluable resource to give a medical "snapshot" of a genetic disorder or topic.
Try a search of the database with a keyword from this current practical or a specific genetic disease.
This excellent resource is provided by the National Library of Medicine (NLM), National Center for Biological Information (NCBI) website. The NCBI site in addition to having key databases for genomic and molecular biology research, and PubMed literature database, has setup a Bookshelf providing free online full cross-referenced and searchable textbooks. The OMIM resource (above) is also located within the NCBI website.
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Link to next page in this GIT Laboratory - Respiratory Development This page starts the laboratory by revising the first 3 weeks of development. |
Lecture 10 - Respiratory Development Thu 13:00 - 14:00 Australian School Business 119 (K-E12-119)
Laboratory 06 - Thu 10:00 - 12:00 Wallace Wurth 106/108 (K-C27-106)
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atresia - (Greek, a = without + tresis = perforation) Term used for anatomical closing or absence of a cavity or opening that should exist. Used as an antomical, pathological and clinical term: esophageal atresia, biliary atresia, duodenal atresia, jejunal atresia, choanal atresia, urethral atresia, bronchial atresia.
biliary cells - The liver epithelial cell formed from hepatoblast differentiation (hepatoblasts form from endoderm). (More? Gastrointestinal Tract - Liver)
buccal (Latin, bucca = cheek) term used to relate to the mouth (oral cavity). (More? GIT Notes)
buccopharyngeal membrane - (oral membrane) (Latin, bucca = cheek) Forms the external upper membrane limit (cranial 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 "oral opening" of the gastrointestinal tract. (see also 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. (More? buccopharyngeal membrane | GIT Notes)
enteroendocrine cells - Endocrine cells found within the epithelium of the gastrointestinal tract. (More? Endocrine Notes)
extrahepatic bile ducts - (EHBDs) is used to describe the hepatic, cystic, and common bile ducts. (More? GIT Notes - Gall Bladder)
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. (More? Gastrointestinal Tract - Stomach | Gastrointestinal Tract Notes | Respiratory Notes)
gall bladder - The septum transversum differentiates to form the hepatic diverticulum and the hepatic primordium, these two structures together will go on to form different components of the mature liver and gall bladder. In the adult, the gall bladder is a site of bile salt storage and concentration, to then be released into the small intestine where they act to solubilize dietary lipids by their detergent effect. Bile salts are a cholesterol derivative (breakdown product). (More? Gastrointestinal Tract - Gall Bladder | Liver Notes)
greater omentum - The greater omentum is the peritoneal fold extending from the greater curvature of the stomach and hanging down "like an apron" ventrally over the small intestine. It forms initially in the embryo and fetus as a loop of the dorsal mesentery, which later fuses to form a single sheet attached to the posterior body wall. The lesser omentum is a smaller ventral peritoneal fold extending from lesser curvature of the stomach to liver. (More? GIT Notes)
hepatic - (Greek, hepato = liver) relates to the liver and its associated structures. (More? Gastrointestinal Tract - Liver)
hepatic duct - the liver excretory duct, joins with gall bladder cystic duct to form the common bile duct. (More? Gastrointestinal Tract - Liver)
hepatoblast - The undifferentiated liver progenitor cell formed initially from endoderm, which willlater form both hepatocytes and biliary cells. (More? Gastrointestinal Tract - Liver)
hepatocyte - The functional liver cell formed from hepatoblast differentiation (hepatoblasts form from endoderm). (More? Gastrointestinal Tract - Liver)
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. (More? Gastrointestinal Tract Notes | Urogenital Notes)
interstitial cells of Cajal - (ICC) Neural cells located in the gastrointestinal tract (enteric nervous system) located within the smooth muscle wall (tunica muscularis) that act as electrical pacemakers to coordinate muscular slow wave contraction propagation. (More? Neural Crest Notes)
insulin - A protein hormone, produced by specialized cells of the pancreas, that regulates glucose uptake; a signal for the absorptive state; promotes the synthesis of glycogen and inhibits its breakdown. (More? Endocrine Development - Pancreas)
intestinal immune system - consists of a system of functional regions and cells including: Peyer's patches, isolated lymphoid follicles, cryptopatches and mesenteric lymph nodes.
lesser omentum - The smaller of two splanchnic mesoderm peritoneal folds (lesser/greater), the lesser extends from lesser curvature of the stomach to liver. The greater omentum extends from the greater curvature of the stomach and hanging down "like an apron" ventrally over the small intestine. (More? GIT Notes)
meconium - The gastrointestinal contents that accumulate in the intestines during the fetal period. This material is a mixture of liver and glandular secretions, amniotic fluid, and cellular debris. Meconium is also used to describe the first postnatal rectal discharge from the neonate. Fetal stress in the third trimester or at parturition can lead to premature meconium discharge into the amniotic fluid, ingestion by the fetus and damage to respiratory function. Damage to placental vessels meconium myonecrosis may also occur. (More? Birth)
mesogastrium - The developmental term for the splanchnic mesoderm forming early mesenteries (dorsal and ventral) that support the developing gastrointestinal tract. The majority of the ventral mesentery is developmentally lost at the level of the midgut and the dorsal mesentery remains in the adult, through which blood vessels, nerves and lymph connects to the gastrointestinal wall. Note that specific visceral organs also develop within each mesogastrium. (More? GIT Notes)
midgut - The middle of the three part/division (foregut - midgut - hindgut) of the early forming gastrointestinal tract. The midgut is initially connected on the ventral embryo surface to the external yolk sac by a yolk stalk, a narrow tubular connection. The midgut forms all the tract from beneath the stomach (duodenum, small intestine and large intestine) to the distral transverse colon. The midgut develops as an external loop "herniated" ventrally, until early fetal growth of the body wall recaptures this external loop, which also undergoes a rotation about the superior mesenteric artery to establish the adult anatomical position. (More? Gastrointestinal Tract - Intestine | Gastrointestinal Tract Notes)
neural crest - cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types (= pluripotential). Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG). Neural crest cells also migrate into the mesoderm to form the enteric nervous system of the gut. (More? Neural Crest Notes)
pancreas - The gastrointestinal tract associated organ with both exocrine (pH change and digestive enzyme secretion) and endocrine (hormone secretion) functions. In humans, the pancreas develops at the foregut/midgut junction (the septum transversum) and initially form connected to the gastrointestinal tract as two pancreatic buds (dorsal and ventral endoderm) which later fuse to form a single organ. The pancreas exocrine function (alkylate acidic stomach contents and amylase protein digestion) begins mainly fter birth. The endocrine function (alpha cell - glucagon, delta cell - somatostatin, beta cell - insulin) can be measured from 10 to 15 weeks onward. (More? Gastrointestinal Tract - Pancreas | Endocrine Development - Pancreas)
parenchymal - (parenchyma) Histological term used to describe the functional cells of an organ, tissue or structure. The term is often paired with stromal (stroma), which describes the supportive cells within an organ, tissue or structure.
peritoneal cavity - Anatomical body cavity in which the lower body organs lie: intestines, liver, bladder, uterus, ovary. The peritoneal cavity forms initially from two separate regions of the early intraembryonic coelom (formed in the lateral plate mesoderm), which with embryo folding, fuse to form a single cavity. Note the single intraembryonic coelom forms all three major body cavities: pericardial, pleural, peritoneal. (More? Coelomic Cavity Notes)
pleuroperitoneal membrane - An early embryonic membrane that forms inferiorly at the septum transversum to separate peritoneal cavity from pleural cavity.
septum transversum (transverse septum) A mesodermal region in the early embryo. Identified externally as the junctional site between amnion and yolk sacs, and internally (within the embryo) lying directly beneath the heart and at the foregut/midgut junction. This ventro-dorsal "plate" of mesoderm contributes several structures including: the central tendon of diaphragm and some of the liver. The transverse septum has an important structural role in early embryonic development and is pierced by the gastrointestinal tract. (More? Gastrointestinal Tract Notes | Liver Notes | Respiratory Development - Diaphragm)
splanchnic mesoderm - Gastrointestinal tract (endoderm) associated mesoderm formed from the splitting of the lateral plate mesoderm. This mesoderm is the embryonic origin of the gastrointestinal tract connective tissue, smooth muscle, blood vessels and contribute to organ development (pancreas, spleen, liver). The same lateral plate mesoderm lying above the buccopharygeal membrane will form the heart. The cavity in the lateral plate mesoderm (intraembryonic coelom) will form the three major body cavities including the peritoneal cavity of the gut. The other half of the lateral plate mesoderm (somatic mesoderm) is associated with ectoderm and the body wall.
spleen - The spleen develops within the gastrointestinal tract dorsal mesogastrium mesenchyme. With folding it is located on the left side of the abdomen and has a role initially in blood (haematopoisis, blood cell formation) and later immune system development. The spleen's haematopoietic function is lost with fetal development and lymphoid precursor cells migrate into the developing organ. (More? Spleen Notes
stenosis - Term used to describe an abnormal narrowing, usually in relation to a tube. For example, in a blood vessel or in the gastrointestinal tract. (More? Gastrointestinal Tract Abnormalities)
stomach - Gastrointestinal tract (GIT) foregut organ that has a major function in digestion. In humans, during week 4 initially as a dilatation of the foregut lying behind the heart. Differential growth of the ventral and dorsal walls establishes the greater curvature of the stomach and second rotation (of 90 degrees) occurs on the longitudinal axis establishing the adult anatomical orientation of the stomach. (More? Gastrointestinal Tract - Stomach)
stomadeum - (stomadeum) 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. (More? Gastrointestinal Tract Notes | Head Notes)
stromal - (stroma) Histological term used to describe supportive cells within an organ, tissue or structure. The term is often paired with parenchymal, which describes the functional cells of an organ, tissue or structure.
(septum transversum) see septum transversum a mesodermal region in the early embryo.
atresia - (Greek, a = without + tresis = perforation) Term used for anatomical closing or absence of a cavity or opening that should exist. Used as an antomical, pathological and clinical term: esophageal atresia, biliary atresia, duodenal atresia, jejunal atresia, choanal atresia, urethral atresia, bronchial atresia.
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