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USMLE GI > Embryology > Flashcards

Embryology Flashcards

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USMLE® Step 1 flashcards
1
Q

Where does the foregut extend from?

A

Esophagus to ampulla of vater (2nd part of duodenum)

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2
Q

Where does the midgut extend from?

A

Lower duodenum to proximal 2/3s of transverse colon

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3
Q

Where does the hindgut extend from?

A

Distal 1/3 of transverse colon to anal canal above the pectinate line

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4
Q

During what week of development does the midgut herniate through the umbilical ring?

A

6th

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5
Q

During what week of development does the midgut return to the abdominal cavity?

A

10th

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6
Q

How does the midgut rotate when returning back into the abdominal cavity?

A

270° counterclockwise (also rotates around SMA)

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7
Q

Name 2 extremely common ventral wall defects

A
  • Gastroschisis

- Omphalocele

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8
Q

What ventral wall defect is associated with chromosomal abnormalities (e.g trisomy 13, 18 and Beckwith-Wiedemann)

A

Omphalocele

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9
Q

What is the main difference between Gastroschisis and Omphalocele?

A
  • Gastroschisis - guts not covered peritoneum or amnion

- Omphalocele - Gut contents covered by peritoneum and amnion (gray shiny sac)

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10
Q

What is the etiology of gastroschisis?

A

Abdominal contents extrude through abdominal folds (typically right of umbilicus)

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11
Q

What is the etiology of Omphalocele?

A

Failure of lateral walls to migrate at umbilical ring

- Causes persistant midline herniation of abdominal contents into umbilical cord

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12
Q

What is the cause of a congenital umbilical hernia?

A

Failure of the umbilical ring to close after physiological herniation of the midgut.

  • May get worse with crying (increased intra-abdo pressure)
  • Small defects close spontaneously
  • May be associated with congenital disorders
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13
Q

What is the most common tracheoesophageal anomaly?

A

Esophageal atresia with distal tracheoesophageal fistula (85%)

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14
Q

How does esophageal atresia with TEF usually present?

A
  • In utero - polyhydramnios (inability of fetus to swallow amniotic fluid)
  • Neonates drool, choke, vomit within 1st feeding
  • Cyanosis due to laryngospasm (avoid refluc-related aspiration)
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15
Q

What clinical test can diagnose esophageal atresia (with TEF)?

A

Failure to pass nasogastric tube into stomach

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16
Q

In pure esophageal atresia what does CXR show?

A

Gasless abdomen

- Unlike pure TEF, or EA with TEF where there will be a prominent gastric bubble

17
Q

What does pure TEF (transesophageal fistula) show?

A
  • H-type fistula

- Can see a prominent gastric bubble

18
Q

What are the 3 types of tracheoesophageal anomaly?

A
  • Pure esophageal atresia
  • Pure tracheoesophageal fistula
  • Esophageal atresia with distal transesophageal fistula
19
Q

What do intestinal atresias present with?

A

Bilious vomiting and abdominal distension within first 1-2 days of life

20
Q

What can be seen on imaging of duodenal atresia?

A
  • Double bubble on X-ray (dilated stomach, proximal duodenum
21
Q

What syndrome may be associated with duodenal atresia?

A

Down syndrome

22
Q

What are the severe complications of jejunal and ileal atresia?

A
  • Disruption of mesenteric vessels (typically SMA)
  • Causes ischemic necrosis of fetal intestine
  • > Segmental resorption: bowel becomes discontinuous
23
Q

What may be seen on imaging in jejunal and ileal atresia?

A
  • Triple bubble (dilated stomach, duodenum, proxima jejunum)
  • Gasless colon
24
Q

What is the most common cause of gastric outlet obstruction in infants?

A

Hypertrophic pyloric stenosis

25
Q

What are the features of hypertrophic pyloric stenosis?

A
  • Palpable olive-shaped mass in epigastric region (visible peristaltic waves)
  • Nonbilious projectile vomiting at 2-6 weeks
26
Q

Wha does imaging show in hypertrophic pyloric stenosis?

A

US shows thickened and lengthened pylorus

27
Q

What metabolic disorder is caused by pyloric stenosis?

A

Hypokalemic hypochloremic metabolic alkalosis (secondary to vomitting of gastric acid)

28
Q

What may predispose to hypertrophic pyloric stenosis?

A

Macrolide exposure (also more common in firstborn males)

29
Q

What is the treatment of hypertrophic pyloric stenosis?

A

Surgical incision of pyloric muscles (pyloromyotomy)

30
Q

What is an Annular pancreas?

A

Abnormal rotation of ventral pancreatic bud forms a ring of pancreatic tissue -> encircles 2nd part of duodenum, may cause duodenal narrowing and vomiting

31
Q

What does the ventral pancreatic bud form?

A
  • Uncinate process
  • Main pancreatic duct
  • Pancreatic head (partly)
32
Q

What does the dorsal pancreatic bud form?

A
  • Body
  • Tail
  • Isthmus
  • Accessory duct
  • Part of pancreatic head
33
Q

What is pancreas divisum?

A
  • Ventral and dorsal parts of the pancreas fail to fuse at 7 weeks of development.
  • Common and often asymptomatic
  • May cause chronic abdo pain and/or pancreatitis

USMLE GI (4 decks)

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