EXAM #1: EMBRYOLOGY OF THE GI SYSTEM Flashcards
What germ layer do the stomodeum and protodeum develop from?
Ectoderm
What are the derivatives of the foregut?
Pharynx to duodenum distal to the bile duct, plus:
- Liver
- Biliary apparatus
- Pancreas
- Respiratory system
What artery supplies the foregut?
Celiac artery
What are the midgut derivatives?
Duodenum distal to the bile duct to the right half of the transverse colon
What artery supplies the midgut?
SMA
What are the derivatives of the Hindgut?
Distal half of the transverse colon to the superior part of anal canal, plus:
- Bladder epithelium
- Most of the urethra
What artery supplies the Hindgut?
IMA
What part of the primitive gut does the respiratory system develop from?
Foregut
Describe the normal development of the esophagus.
1) Single tube
2) Branching of a lung bud and foregut from common tuve
3) Trachea and respiratory passageway are separted by tracheoesophageal folds that form a septum
4) Esophagus elongates
Note that growth of the epithelium in the lumen of the esophagus nearly obstructs the esophagus and then re-canalizes
What is a Short Esophagus?
Failure of the esophagus to elongate pulls some of the stomach into the thoracic cavity that can lead to lung hypoplasia
What is esophageal atresia?
Failure of the esophagus to form
What is tracheoesophageal fistula?
- Proximal esophageal atresia
- Fistula forms between trachea and distal esophageal segment
What is esophageal stenosis?
Narrowing of the esophageal lumen
What are the three mechanisms that cause esophageal stenosis?
1) Sequestration of respiratory tissue elements
2) Myenteric plexus damage that causes hypertrophy (muscularis mucosa)
3) Mucosal diaphragm
What vascular anomaly can lead to esophageal stenosis?
4th branch on the LEFT side of the aortic arch; an anomalous right subclavian retroesophageal artery
What is the eponym for an anomalous right subclavian retroesophageal artery?
Lusorian artery
Describe the normal development of the stomach.
1) Expansion of primitive gut tube
2) More dorsal growth than ventral
3) 90 degree CLOCKWISE rotation
4) Slight pivot from growing esophagus
What part of the primitive stomach becomes the greater curvature?
Dorsal
What part of the primitive stomach becomes the lesser curvature?
Ventral
What is the LARP mnemonic?
Left= Anterior Right= Posterior
What is Infantile Hypertrophic Pyloric Stenosis?
Hypertrophy of the pyloric sphincter in the neonate
What is the US characteristic that is pathognomonic for an Infantile Hypertrophic Pyloric Stenosis?
Sonolucent donut
What is the hallmark sign of Infantile Hypertrophic Pyloric Stenosis?
Non-bilious projectile vomiting
What causes duodenal stenosis?
Incomplete recanalization of the duodenum
What causes duodenal atresia?
Complete failure of recanalization
Mutations in what growth factor have been implicated in duodenal obstruction?
Sonic Hedge Hog
What x-ray findings is pathogmnemonic for duodenal atresia?
Double Bubble Sign
What is the most common cause of jejunal and ileal atresia?
Vascular accident, NOT failure of recanalization
What are the three stages of midgut rotation? What happens during these stages?
1) Herniation into the umbilical cord
2) Reduction back into the abdominal cavity
3) Fixation to posterior abdominal wall
What happens to the cranial and caudal limbs in midgut rotation? What is the axis of rotation?
Axis= SMA
Cranial= superior to SMA
- Undergoes rapid elongation
- Comes back in to left
Caudal= inferior to SMA
- Comes back in to right and inferior
What direction does the midgut rotate?
1) 90 degrees COUNTER-CLOCKWISE going OUT
2) 90 degrees counter clockwise
3) Additional 90 degrees COUNTER-CLOCKWISE
What is Omphalocele?
Failure of midgut reduction–results in external abdominal contents
What is a midgut nonrotation?
Midgut ROTATES, but only the first 90 degrees
What is the manifestation of midgut nonrotation?
Reversal of midgut contents–left sided-colon and right-sided small intestine
What is reversed rotation of the midgut?
270 degree rotation CLOCKWISE instead of counter- clockwise
What is the manifestation of reversed midgut rotation?
- Duodenum is anterior to the SMA
- Transverse colon is posterior to SMA
What is the mixed rotation of the midgut?
- Cranial limb rotates but caudal limb doesn’t in first rotation
- 2nd rotation, only caudal limb rotates
What is the manifestation of mixed rotation of the midgut?
1) Cecum lies inferior to pylorus
2) Peritoneal bands form over duodenum
3) Duodenal obstruction
- Peritoneal bands
- Volvulus
How does a midgut volvulus appear on imaging?
1) “Corkscrew sign” on CT
2) Whirpool sign on US
What is a Meckel’s Diverticulum?
Persistence of the vitelline duct that forms an outpocketing of the ileum–a TRUE diverticulum
What type of diverticulum is a Meckel’s Diverticulum?
True–all walls involved
What causes ulceration of a Meckel’s Diverticulum?
Heteroptoic parietal cells that screte HCl
How is the cloaca normally partitioned?
1) Urorectal septum divides the cloaca (terminal hindgut) into dorsal and ventral portions
- Ventral= urogenital sinus
- Dorsal= rectum
2) Urorectal septum contacts cloacal membrane forming:
- Anal membrane
- Urethral membrane
3) Anal membrane lies at bottom of proctodeum
What is the division of the dual derivation of the anal canal?
Pectinate line
- Proximal= hindgut
- Distal= ectoderm
What is the white line in the anal canal?
Division between internal and external sphincters
What arteries and veins supply the anal canal from the hindgut?
Superior rectal artery and veins
What lymph nodes supply the anal canal above the pectinate line?
IM
What arteries and veins supply the anal canal below the pectinate line?
Inferior rectal
What lymph nodes drain the anal canal distal to the pectinate line?
Superficial inguinal
Describe the innervation of the anal canal.
Superior to pectinate line= ANS
Inferior to pectinate line= Inferior rectal nerve
No pain with issue superior to pectinate line*
What is a Congenital Megacolon?
Absence of Myenteric Plexus in the colon that leads to contraction and dilation similar to achalasia
What is an annular pancreas?
Bilobed pancreas wraps around the duodenum
What can an annular pancreas cause?
Duodenal stenosis
What sign can be present with an annular pancreas on x-ray?
Double bubble
