Block 2 Anatomy Embryo GI system - Cell Bio Transduction part 1 Flashcards
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Describe the morphology of the developing gut tube including the cloacal membrane, allantois and vitelline duct
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Cloaca
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- Latin word for sewer is cloaca
- This primitive portion of posterior hindgut receives outflow of GI tract and urogenital system
- Urorectal septum divides cloaca into rectum and precursor of urinary bladder
- Covered more extensively with urogenital development
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Allantois
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Allantois: duct connecting the developing bladder to the placenta so wastes can be removed
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Vitelline duct
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Vitelline duct: connection between the yolk sac and gut tube
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Origins of Different Components of Gut Tube
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Origins of Different Components of Gut Tube
- Luminal Lining Epithelium from Endoderm
- Resident Cells in lamina propria, submucosal CT, muscularis externa, and adventital CT from splanchnic mesoderm
- Myenteric (Auerbach’s) plexus and Submucosal (Meissner’s) plexus from neural crest
- Lymphoid tissue from bone marrow (mesoderm)
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Origins of Components of Liver, Pancreas, and Gall Bladder
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Origins of Components of Liver, Pancreas, and Gall Bladder
- Hepatic parenchymal cells, pancreatic acinar cells, islet tissue, luminal lining of gall bladder from endoderm
- CT in capsules and rest of organ, blood vessels, smooth muscle in wall of gall bladder from mesoderm.
- In liver, CT and blood vessels from septum transversum, rest from splanchnic mesoderm
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Bottom Line
- If it is derivied from the gut tube itself, it is endoderm
- If it is associated tissue, it is mesoderm
- If it is neural, it is neural crest
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Divisions of Primitive Gut Tube
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Divisions of Primitive Gut Tube
- Foregut-from buccopharyngeal membrane to anterior intestinal portal
- Midgut-from anterior to posterior intestinal portal
- Hindgut-from posterior intestinal portal to cloacal membrane
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Blood Supply to Embryonic Divisions of Gut Tube
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Blood Supply to Embryonic Divisions of Gut Tube
- Lower foregut-celiac trunk
- Midgut-superior mesenteric artery
- Hindgut-inferior mesenteric artery
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Cranial Foregut Derivatives
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Cranial Foregut Derivatives
- Epithelium lining posterior oral cavity
- Thyroid epithelium
- Respiratory diverticulum
- Epithelium of auditory tube
- Epithelium of palatine tonsils
- Epithelium of parathyroids
- Epithelium of thymus
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Caudal Foregut Derivatives
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Caudal Foregut Derivatives
- Oropharynx and Esophagus
- Stomach
- First part of duodenum
- Liver, pancreas, and gall bladder
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Midgut Derivatives
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Midgut Derivatives
- Second part of duodenum
- Ileum and jejunum
- Cecum and vermiform appendix
- Ascending colon
- Transverse colon to middle
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Hindgut Derivatives
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Hindgut Derivatives
- Second half of transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Anus to anal valves (pectinate line)
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Gastric Rotation
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Gastric Rotation
- Stomach forms from dilation of caudal foregut
- Has both dorsal and ventral mesogastrium
- First rotation carries dorsal mesogastrium from dorsal to ventral, elongating it extensively to form greater omentum
- Second rotation brings cardiac stomach down and to left, pyloric up and to right
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Results of Midgut Rotation
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Results of Midgut Rotation
- As midgut loop is reduced into peritoneal cavity, parts of it become attached to body wall by resorption of mesenteries
- Also, cecum, vermiform appendix, and first part of ascending colon end up in right lower quadrant of abdomen
- Ascending colon becomes secondarily retroperitoneal
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MOLECULAR REGULATION OF GUT TUBE DEVELOPMENT I
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MOLECULAR REGULATION OF GUT TUBE DEVELOPMENT I
- A gradient of retinoic acid (high caudally, low cranially) causes differential expression of regulatory genes
- The regulatory genes define the structure of the different regions of the gut tube
- SOX2 esophagus and stomach
- PDX3 duodenum
- CDXC small intestine
- CDXA large intestine and rectum
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MOLECULAR REGULATION OF GUT TUBE DEVELOPMENT II
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MOLECULAR REGULATION OF GUT TUBE DEVELOPMENT II
- The lower gut tube produces a gradient of Sonic hedgehog (SHH)
- SHH induces differential expression of Hox genes by the surrounding mesoderm
- The differential Hox expression creates the regional differences between the small intestine, cecum, colon, and cloaca
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Hepatic Development
Hepatic Development
* Liver diverticulum forms from caudal foregut
* Liver diverticulum grows into surrounding splanchnic mesoderm and septum transversum and branches
* Branches are called hepatic cords and form ducts and hepatic parenchymal cells
* CT and blood vessels in liver from splanchnic mesoderm and septum transversum
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Gall Bladder Development
Gall Bladder Development
* Cystic diverticulum (precursor of gall bladder) branches off hepatic diverticulum
* Luminal epithelum from endoderm
* Mural structures from splanchnic mesoderm
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Pancreatic Development
Pancreatic Development
* Ventral pancreatic bud forms adjacent to cystic diverticulum
* Ventral pancreatic bud branches
* On opposite side, dorsal pancreatic bud forms
* Dorsal (main body and tail) and ventral buds then fuse (head)
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Peritoneal Status of GI organs I
Peritoneal Status of GI organs I
* Retroperitoneal viscera (never in peritoneal cavity)- esophagus to diaphragm and rectum
* Intraperitoneal viscera-(always projecting into peritoneal cavity) abdominal esophagus, some of gall bladder, stomach, some of duodenum, jejunum, ileum, cecum, vermiform appendix, transverse colon, sigmoid colon
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Peritoneal Status of GI Organs II
Peritoneal Status of GI Organs II
## Footnote
Secondarily retroperitoneal viscera-(transitionally “in” peritoneal cavity but outside peritoneal cavity in adult)-most of duodenum, most of pancreas, ascending colon, descending colon
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Septation of Caudal Hindgut
Septation of Caudal Hindgut
* Urorectal septum divides cloaca into rectum and urinary bladder
* Thus, upper rectum and urinary bladder derived from endodermally derived epithelium
* Anus forms from ectodermally derived anal pit
* Pectinate line is approximate boundary between two rudiments
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Embryology of Rectoanal Canal I
Embryology of Rectoanal Canal I
* Above pectinate line, endodermally derived epithelium, autonomic innervation (insensitive mucosa), superior rectal artery and vein, inferior mesenteric nodes
* Below pectinate line, ectodermally derived epithelium, inf. rectal nerve (sensitive mucosa), inferior rectal artery and vein, superficial inguinal nodes
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Embryology of Rectoanal Canal II
Embryology of Rectoanal Canal II
* Carcinoma in upper part painless, check inferior mesenteric nodes for metastasis
* Carcinoma in lower part painful, check superficial inguinal nodes for metastasis
* Rectoanal junction (simple columnar to stratified squamous keratinized) at white line (of Marshall)
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Tracheoesophageal Fistulas
Tracheoesophageal Fistulas
Congenital defects associated with the GI system
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Meckel’s Diverticulum
Meckel’s Diverticulum
* Ileal (Meckel) diverticulum
* Most common congenital GI defect
* Remnant of vitelline duct
* Middle of midgut-ileum
* Usually asymptomatic
* May contain ectopic gastric mucosa \> ulceration
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Rule of Two’s
Rule of Two’s
* 2% of the population
* 2 feet from the ileocecal valve
* 2 inches in length
* 2% are symptomatic
* 2 types of common ectopic tissue (gastric and pancreatic)
* 2 years is the most common age at clinical presentation
* 2 times more boys are affected
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congenital defects associated with the GI system
congenital defects associated with the GI system
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Abnormal rotation
Abnormal rotation
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Congenital Defects
Congenital Defects
* Omphalocele-Defect in anterior abdominal wall covered by peritoneum and amnionic sac-failed reduction? 1/5000-1/10,000 births
* Gastroschisis-Rare defect in anterior abdominal wall without peritoneal and amnionic covering-lateral fold defect?
* Congenital megacolon (Hirschsprung disease)-failed NC migration to colon \> poor peristalsis \> colonic dilation (upstream from aganglionic segment)
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Atresia
Atresia
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Fistulas
Fistulas
