Slideshow is from the University of Michigan Medical School's M1 Embryology sequence View additional course materials on Open.Michigan: openmi.ch/med-M1Embryology

1. Author(s): Matthew Velkey, 2009 License: Unless otherwise noted, this material is made available under the terms of the Creative Commons Attribution – Non-Commercial – Share Alike 3.0 License : http://creativecommons.org/licenses/by-nc-sa/3.0/ We have reviewed this material in accordance with U.S. Copyright Law and have tried to maximize your ability to use, share, and adapt it. The citation key on the following slide provides information about how you may share and adapt this material. Copyright holders of content included in this material should contact [email_address] with any questions, corrections, or clarification regarding the use of content. For more information about how to cite these materials visit http://open.umich.edu/education/about/terms-of-use. Any medical information in this material is intended to inform and educate and is not a tool for self-diagnosis or a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional. Please speak to your physician if you have questions about your medical condition. Viewer discretion is advised : Some medical content is graphic and may not be suitable for all viewers.

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3. Development of the Gastrointestinal System Matt Velkey Spring 2009

7. Gastrulation: Epiblast cells migrate through the primitive streak. Definitive (embryonic) endoderm cells displace the hypoblast. Mesoderm spreads between endoderm and ectoderm. Langman’s Medical Embryology, 9 th ed. 2004.

8. Early mesodermal patterning: (buccopharyngeal membrane) Specific regions of the epiblast migrate through the streak at different levels and assume different positions within the embryo: Source Undetermined Cranial to caudal: Notochord (n) Paraxial mesoderm (pm) Intermediate mesoderm (im) * Lateral plate mesoderm (lpm) Extraembryonic mesoderm (eem)

9. The developing endoderm (yellow) is initially open to the yolk sac (the cardiac region is initially most anterior)… Longitudinal folding at both ends of the embryo and lateral folding at the sides of the embryo bring the endoderm inside and form the gut tube. Endoderm Langman’s Medical Embryology, 9th ed. 2004.

10. Folding creates the anterior and posterior intestinal portals (foregut and hindgut, respectively) The cardiac region is brought to the ventral side of the developing gut tube. Cloacal membrane Langman’s Medical Embryology, 9th ed. 2004. Juxtaposition of ectoderm and endoderm at: Oropharyngeal (buccopharyngeal) membrane - future mouth Cloacal membrane - future anus

11. Gut-associated organs begin to form as buds from the endoderm: (e.g., thyroid, lung, liver, pancreas) Midgut opening to the yolk sac progressively narrows Langman’s Medical Embryology, 9th ed. 2004.

12. By the end of the first month: The stomach bulge is visible, Dorsal pancreas has begun to bud Connection of the midgut to the yolk sac is reduced to a yolk stalk Langman’s Medical Embryology, 9th ed. 2004.

14. Foregut: pharynx thyroid esophagus parathyroid glands stomach tympanic cavity proximal duodenum trachea, bronchi, lungs liver, gallbladder pancreas Midgut: proximal duodenum to right half of transverse colon Hindgut: left half of urinary bladder transverse colon to anus Gut tube proper Derivatives of gut tube (These three regions are defined by their blood supply)

15. 25 days 32 days Celiac artery supplies the foregut Superior mesenteric artery supplies the midgut Inferior mesenteric artery supplies the hindgut Langman’s Medical Embryology, 9 th ed. 2004.

16. Gut = bilayered tube (endoderm surrounded by mesoderm) Regional gut tube patterning and organogenesis require bi-directional endoderm-mesoderm cross-talk and inductive signals from other nearby structures Regional patterning of the gut tube Source Undetermined

19. Hedgehog signaling is important for concentric (radial) patterning of the entire gut tube Morphogen: induces different cell fates at different concentrations of signal Source Undetermined Wheater’s Functional Histology M. Velkey. Hh Fetus High Hedgehog concentration inhibits muscle formation; Sm. Musc. Sm. Musc Low Hedgehog concentration stimulates muscle differentiation Adult Esophagus

20. Esophageal/Gastric border Esophagus Stomach Cranial-caudal pattern of the gut tube is played out as regional organ differentiation. Distinct borders form. Source Undetermined

21. Pyloric border (gastric/duodenal) Stomach Duod. Stomach Duodenum Source Undetermined Source Undetermined

27. Once specified, the hepatoblasts proliferate and invade the septum transversum Angioblasts (endothelial cell precursors) are found next to the thickening pre-hepatic endoderm before invasion of the liver bud; these endothelial cells supply critical growth signals Three signals for liver formation: FGF from cardiac mesenchyme; BMPs from septum transversum mesenchyme, VEGF from endothelial cells (anlage formation) Source Undetermined

31. Defects associated with gut herniation and rotation: oomphaocoele Langman’s Medical Embryology, 9 th ed. 2004.

32. Defects associated with gut herniation and rotation: vitelline duct abnormalities Langman’s Medical Embryology, 9 th ed. 2004.

33. Defects associated with gut herniation and rotation: abnormal rotation Absent or incomplete secondary rotation Reversed primary rotation (90° CW) Langman’s Medical Embryology, 10 th ed. 2006.

34. Defects associated with gut herniation and rotation: volvulus Fixation of a portion of the gut tube to the body wall; subsequent rotation causes twisting of the tube, possibly resulting in stenosis and/or ischemia. Original Image: Carlson - Human Embryology and Developmental Biology, 4th Edition. Image of defects with gut herniation and rotation removed.