Overview of Gastrointestinal Embryology
Transcript of Overview of Gastrointestinal Embryology
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Harvard-MIT Division of Health Sciences and Technology
HST.121: Gastroenterology, Fall 2005
Instructors: Dr. Jonathan Glickman
Overview of Gastrointestinal Embryology
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The Primitive Gut• The primitive gut forms during the 4th week of gestation
when the flat embryonic disc folds in median and horizontal planes to form a tubular structure that incorporates part of the yolk sac into the embryo
• Ventral folding of lateral sides forms the midgut
• Ventral folding of cranial and caudal ends (head and tail folds) form the foregut and the hindgut
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Folding of the Embryonic Disc
Figure removed due to copyright reasons. Please see:
Moore, Keith L., and T. V. N. Persaud. The Developing Human: Clinically Oriented Embryology.
Philadelphia, PA: W.B. Saunders Company, 1998. ISBN: 0721669743.
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Formation of human gastrointestinal tract (A)
Stomach
Heart
Vitelline duct
Allantois
Cloacal membrane
Liver bud
Midgut
Hindgut
Image by MIT OCW.
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The Foregut
• The foregut gives rise to the:– Pharynx – Lower respiratory system– Esophagus – Stomach – Proximal duodenum – Liver and the biliary tree– Pancreas
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Partitioning of the foregut by the tracheoesophageal septum
Figure removed due to copyright reasons. Please see:
Sadler, Thomas W. Langman's Medical Embryology. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins, 1990. ISBN: 0683074938.
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Errors of the Foregut Development
Errors in partitioning of the laryngo-tracheal tube from the esophagus by the tracheo-esophageal septum result in various forms of esophageal atresia and tracheo-esophageal fistulas or EA/TEF (1 in 3000-4500 8 5 % 8 -1 0 % 3 -4 %
Figure by MIT OCW. live births, M>F)
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Tracheoesophageal fistula
Images removed due to copyright reasons.
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Development of the Lumina
Epithelial Plug Vacuolization
Lumen
Recanalization
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Abnormal Development of the Lumina Epithelial Plug Vacuolization
Lumen
Atresia Stenosis Duplication, Cyst or Septum
Recanalization
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Jejunoileal atresia
Image removed due to copyright reasons.
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Congenital Hypertrophic Pyloric Stenosis
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Errors of the Foregut Development
• Congenital Hypertrophic Pyloric Stenosis is the most common congenital anomaly of thestomach and occurs in 1-8:1000 live births with a 4-6:1 M:F ratio
• Pyloric stenosis is a multifactorial andprogressive disease that classically presentswith non-bilious projectile vomiting in the firstfew weeks of life
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The Liver and the Pancreas
Figure removed due to copyright reasons. Please see:
Moore, Keith L., and T. V. N. Persaud. The Developing Human: Clinically Oriented Embryology. Philadelphia, PA: W.B. Saunders Company, 1998. ISBN: 0721669743.
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Errors in Pancreatic Development
• Annular pancreas
• Pancreas divisum
• Ectopic pancreatic tissue
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The Midgut
• The midgut gives rise to: – Distal duodenum – Jejunum and ileum – Appendix – Ascending colon – Proximal transverse colon
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Epithelial cytodifferentiation
Images removed due to copyright reasons.
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Intestinal epithelial differentiation
Images removed due to copyright reasons.
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The Midgut Rotation
• The midgut forms a U-shaped loop that herniates into the umbilical cord during the 6th weeks of gestation
• While in the umbilical cord, the midgut loop rotates 90 degrees
• During the 10th week of gestation, the midgut loop returns to the abdomen, rotating an additional 180 degrees
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Errors in Midgut Rotation
Anything can happen, but it usually doesn’t!
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Errors in Midgut Development
• Omphaloceles result from failure of the intestines to return to the abdominal cavity
• Umbilical hernias occur when intestines do return to the abdomen, but later herniate through the umbilicus
• Gastroschisis is a linear defect of the abdominal wall that permits extrusion of the viscera without involving the umbilicus
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Image removed due to copyright reasons.
Infant with gastroschisis
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Infant with omphalocele
Image removed due to copyright reasons.
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DIFFERENCES BETWEEN GASTROSCHISIS AND OMPHALOCELE Gastroschisis Omphalocele Maternal age Younger Older
Associated anomalies 10% (usually intestinal atresia)
50% (structural and chromosomal)
Sac covering abdominal contents No Yes Liver out through abdominal wall defect No Often Intestinal dysfunction (hypomotility and malabsorption) Yes No
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Remnants of the omphalomesenteric duct (yolk stalk) are found in 1-4%of infants, making them the most common congenital anomaly of the GI
tract
Figure removed due to copyright reasons. Please see:
Moore, Keith L., and T. V. N. Persaud. The Developing Human: Clinically Oriented Embryology.
Philadelphia, PA: W.B. Saunders Company, 1998. ISBN: 0721669743.
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Meckel’s Diverticulum• Meckel’s or ileal diverticulum accounts for up to 80%
of omphalomesenteric remnants
• Typical Meckel’s diverticulum measures 3-5 cm, and is located in the anti-mesenteric wall of the ileum 40-50 cm from the ileocecal valve
• Most symptomatic cases present in childhood
• The M:F incidence ratio is ~1, but there is a 3:1 M:F ratio in clinically symptomatic cases
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The Hindgut• The hindgut gives rise to:
–Distal transverse colon –Descending colon, sigmoid, and rectum – Proximal anal canal (superior to the pectinate
line)
• The caudal part of the hindgut known as thecloaca, is divided by the urorectal septuminto the urogenital sinus and the rectum
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Partitioning of the Cloaca by the Urorectal Septum
Figure removed due to copyright reasons. Please see:
Moore, Keith L., and T. V. N. Persaud. The Developing Human: Clinically Oriented Embryology.
Philadelphia, PA: W.B. Saunders Company, 1998. ISBN: 0721669743.
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Errors in Hindgut Development
Figure removed due to copyright reasons. Please see:
Moore, Keith L., and T. V. N. Persaud. The Developing Human: Clinically Oriented Embryology.
Philadelphia, PA: W.B. Saunders Company, 1998. ISBN: 0721669743.
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Hirschsprung’s Disease
• HD is the partial or total absence of autonomic ganglia resulting from failure of migration of the neural crest cells into the colonic wall during 5th-7th week of gestation
• With an incidence of 1 in 5000 liver births, HD is the most common cause of neonatal colonic obstruction, and can result in congenital megacolon
• HD has been associated with several genetic abnormalities including Trisomy 21, mutations of the RET gene and the endothelin receptor type B gene
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Intraoperative photograph of Hirschsprung's disease
Image removed due to copyright reasons.
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Hirschsprung’s Disease
Figure removed due to copyright reasons. Please see:
Fenoglio-Preiser, Cecilia M., et al. Gastrointestinal Pathology. Philadelphia, PA: Lippincot Williams & Wilkins, 1998. ISBN: 0397516401.
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Hirschsprung’s- submucosal plexus
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Three common operations for Hirschsprung's disease
Image removed due to copyright reasons.