GI Embryology Flashcards by Kyra Porter

development of the GI tract - overview

*formed during the 4th week of gestation
*appears as 4mm hollow tube
*buccopharyngeal and cloacal membranes rupture during 3rd and 7th weeks
*well formed & early function by end of 2nd trimester

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foregut

*esophagus
*stomach
*duodenum
*liver
*gallbladder
*pancreas

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midgut

*jejunum
*ileum
*ascending colon
*transverse colon

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hindgut

*descending colon
*rectosigmoid colon

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esophageal atresia & tracheoesophageal fistula

*often occur together
*50% of infants have associated anomalies (VACTERL or CHARGE)
*many different types

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embryology of esophageal atresia & tracheoesophageal fistula

*normally, foregut is partitioned by a septum into 2 separate tubes:
1. anterior trachea develops cartilaginous rings and lung buds
2. posterior esophagus stretches from pharynx to stomach

*INCOMPLETE TUBULAR SEPARATION may occur, leading to esophageal atresia & tracheoesophageal fistula

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esophageal atresia & tracheoesophageal fistula - associated anomalies

*polyhydramnios in 50% of mothers
*cardio: PDA, VSD, ASD
*GI: imperforate anus, duodenal atresia
*skeletal: vertebral anomalies
*GU: hypospadias
*other: trisomy

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most common type of esophageal atresia & tracheoesophageal fistula

type C: esophageal atresia with DISTAL tracheoesophageal fistula

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esophageal atresia with DISTAL tracheoesophageal fistula (type C)

*85% of total esophageal defects
*esophageal gap 1 to 2 cm
*distal TEF joins trachea at carina
*diagnosis made by placing nasogastric tube (does not go in)
*cough, choking, aspiration with first feed

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esophageal atresia without tracheoesophageal fistula (type A)

*8% of congenital esophageal defects
*absence of gas within the GI tract
*20% will have Down’s syndrome
*if the gap between the esophageal pouches is > 4 cm, primary anastomosis is difficult

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H-type tracheoesophageal fistula

*TEF without esophageal atresia
*3-5% of cases
*rarely have other anomalies
*repeated episodes of pneumonia
*esophagus & trachea otherwise normal

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pyloric stenosis - overview

*sx: non-bilious vomiting
*hypokalemic, hypochloremic metabolic alkalosis
*typically presents between 3-5 weeks of age
*pyloric mass on PE

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pyloric stenosis - incidence and heredity

*most frequent surgical disorder of the stomach
*1.5x increased risk in first-born children
*MALES to females 4-6:1
*possible positive family hx
*premature infants > full term
*increased risk due to maternal smoking
*possible increased risk with bottle feeding vs. breastfeeding
*significant increased risk with use of macrolide antibiotics (esp < 2 weeks of age)

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pyloric stenosis - pathogenesis

*pyloric muscle hypertrophy from gastric peristalsis against closed pyloric canal
*hypergastrinemia with hyperacidity
*elevations of prostaglandins leading to smooth muscle constriction

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pyloric stenosis - clinical presentation

*non-bilious, progressive projectile vomiting
*dehydration
*failure to thrive
*classically presents between 3-6 weeks of age
*elevated serum bicarbonate, decrease in serum chloride and potassium

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pyloric stenosis - diagnosis

*physical exam reveals pyloric mass or “olive”
*UGI (upper GI series)
*sonography! (ultrasound - gold standard)

pyloric stenosis - treatment

*fluid & electrolyte management!! (first step)
*surgical correction: pyloromyotomy

duodenal atresia - overview

*thought to arise from failure of recanalization of duodenal lumina (normally occurs during weeks 8-10 of gestation)
*incidence: 1 in 10,000
*associated with prematurity
*F to M 2:1
*ASSOCIATED WITH DOWN’S SYNDROME
*presents with BILIOUS vomiting

duodenal atresia - clinical presentation

*BILIOUS vomiting
*abdominal distension
*“double bubble” on x-ray (dilated stomach & proximal duodenum)

which disorders classically present with non-bilious vomiting in infancy

*esophageal atresia with tracheoesophageal fistula
*pyloric stenosis

which disorder classically presents with non-bilious vomiting in infants with Down syndrome

*duodenal atresia

duodenal atresia - treatment

*fluid & electrolyte management
*feeding tube for decompression
*antibiotics
*surgical correction = duodenoduodenostomy
*prognosis dependent on associated anomalies

jejunal/ileal atresias

*bilious emesis
*failure to pass meconium
*can be associated with cystic fibrosis
*jejunal atresia can be associated with other malformations

duplications of the GI tract

*rare anomalies consisting of well-developed tubular or spherical structures
*located on the MESENTERIC BORDER
*50% contain gastric mucosa
*presents in infancy if symptomatic
*sx related to obstruction, intussusception, volvulus, perforation, or hemorrhage

malrotation

*failure of the midgut to achieve normal position *predisposes to volvulus of midgut *acute bowel obstruction *bilious emesis *symptomatic -> surgical emergency

malrotation - treatment

*if asymptomatic - controversial *if symptomatic - surgical *Ladd's procedure: -reduction of volvulus -evaluation of intestinal viability -division of Ladd's bands -broadening base of mesenteric peduncle -appendectomy -return of SMALL INTESTINE TO RIGHT ABDOMEN -return of LARGE INTESTINE TO LEFT ABDOMEN

Meckel's Diverticulum - overview

***remnant of the omphalomesenteric (vitelline) duct due to its incomplete obliteration** *ANTIMESENTERIC border of ileum ***TRUE diverticulum** (contains all 3 layers of bowel wall) *rules of 2's: -presents before 2 years of age -within 2 feet of ileocecal valve -2 inches long -2% of population -2 types of ectopic tissue (gastric or pancreatic)

Meckel's Diverticulum - clinical presentation

*bowel obstruction *GI bleeding (usually painless)!! *intussusception

Meckel's Diverticulum - diagnosis

*Meckel's scan (99m-Tc pertechnetate scintigraphy) *needs presence of ectopic gastric mucosa *pre-treatment with H2 blocker

Meckel's Diverticulum - treatment

surgical

Hirschsprung's disease - overview

***absence of intramural ganglion cells** *1 in 5000 live births *4:1 MALE to female *20% of cases are familial *associated with Down's syndrome *85% limited to rectosigmoid colon *aganglionic segment permanently contracted *loss of rectosphincteric reflex (relaxation of anal sphincter during defecation)

Hirschsprung's disease - symptoms

***delayed passage of meconium** (within 48 hours of birth)!! *majority have symptoms within first month to year of life ***failure to thrive *vomiting *intermittent diarrhea *abdominal distension** -complication = Hirschsprung's disease-associated enterocolitis: -acute diarrheal illness -severe dehydration, sepsis

Hirschsprung's disease - diagnosis

*barium enema (unprepared) *rectal mucosal suction biopsy (highest sensitivity/specificity - gold standard) *anorectal manometry (absent RAIR)

Hirschsprung's disease - treatment & prognosis

*tx: surgical removal of aganglionic segment of colon *creation of neo rectum using proximal ganglionic bowel *low mortality today

Hirschsprung's disease - common post-op complications

*persistent constipation *anastomotic strictures *toilet training issues *recurrent enterocolitis *fecal incontinence

omphalocele

***ventral wall defect** *location: **umbilical ring** *size: 4-10 cm *umbilical cord inserts onto sac ***sac present (amnion & peritoneum)** *includes stomach, small bowel, colon, liver, etc ***normal bowel appearance** *malrotation present *associated anomalies common

gastroschisis

*ventral wall defect *location: lateral to cord *size: 3-4 cm *normal insertion of umbilical cord ***sac absent *includes only small bowel typically** *bowel is abnormal (poor motility, absorption, etc) *malrotation present *associated anomalies rare