Development of the GI tract Flashcards

1
Q

When does development of the primitive gut tube begin? What is the internal and external lining derived from?

A

At the 3rd week:

Internal lining derived from endoderm (future epithelial lining)

External lining derived from splanchnic mesoderm

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2
Q

What does the splanchnic mesoderm give rise to?

A

Future musculature and visceral peritoneum, the mesentery is also formed from a condensation of this mesoderm

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3
Q

What are the 2 layers of lateral plate mesoderm?

A
  1. Splanchnic: covers GI tube

2. Somatic: lines body wall

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4
Q

Which section of the gut tube has a ventral mesentery? What is the ventral mesentery derived from and what else does it give rise to?

A

The Foregut, derived from the septum transversum; undifferentiated mesoderm that gets carried to its ventral position during longitudinal folding. Also gives rise to the thoracic diaphragm

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5
Q

What forms the greater and lesser peritoneal sacs?

A

The dorsal and ventral mesenteries divide the foregut cavity into R and L sacs:

  • The L sac becomes the greater sac and continues as the bulk of the peritoneal cavity
  • The R sac becomes the lesser sac, rotates and ends up lying behind the stomach
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6
Q

What does the Lesser peritoneal sac create?

A

The greater omentum; fold of visceral peritoneum that hangs down from the stomach

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7
Q

Name 3 functions of the greater omentum

A
  1. Physically limits the spread of intraperitoneal infections
  2. Immune contribution
  3. Fat deposition
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8
Q

When does the lung bud develop and what does it derive from?

A

The 4th week from the endoderm

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9
Q

Name 2 conditions that can occur as a result of abnormal positioning of the tracheoesophageal septum

A
  1. Proximal blind ended esophagus

2. Tracheoesophageal fistula

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10
Q

Which glands are formed from the ventral and dorsal mesentery?

A

Ventral: Liver, biliary system, pancreas (uncinate process and inferior head)

Dorsal: pancreas majority (superior head, neck, body, tail)

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11
Q

How does the stomach’s rotation influence positioning of the surrounding nerves?

A

The VAGUS n follows the stomach’s rotation:

  • L vagus: ends up on the anterior surface
  • R vagus: ends on the posterior surface
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12
Q

What organs/structures does the foregut give rise to? (6)

A
  1. Esophagus
  2. Stomach
  3. Pancreas, liver, gallbladder
  4. Duodenum (proximal to the entrance of the bile duct)
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13
Q

What organs/structures does the midgut give rise to? (7)

A
  1. Distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 transverse colon
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14
Q

Why does physiological herniation occur?

A

Since the abdominal cavity is too small to accommodate the rapid simultaneous growth of the liver and the intestinal loop, the intestines must herniate into the umbilicus temporarily

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15
Q

How does the rotation of the stomach influence the duodenum?

A

As the stomach rotates the duodenum grows in a C shaped loop, gets pushed right and then against the posterior abdominal wall (some parts are retroperitoneal)

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16
Q

Why is the descent of the cecal bud important and what happens if this fails to occur?

A

Ensures the ascending colon lengthens, without this descent you may have a sub-hepatic cecum

17
Q

Name 3 things that can occur as a result of a persisting vitelline duct

A
  1. Cyst that can become inflamed
  2. Fistula (contents can dribble out)
  3. Meckel’s diverticulum: a persisting pouch of endoderm
18
Q

What are the potential consequences of having a Meckel’s diverticulum?

A

The mucosa can contain gastric and pancreatic tissue that can produce cells secreting acid and/or proteolytic enzymes. If the secretions are high enough it can cause an ulceration

19
Q

What is the rule of 2’s in Meckel’s diverticulum? (5 things)

A

2% population, 2 feet from the ileocecal valve, 2 inches long, usually detected in under 2s, 2:1 male: female

20
Q

What does Meckel’s diverticulum mimic?

A

Early stages of appendicitis

21
Q

What is recanalization? What can happen if it’s unsuccessful? Where is it most common?

A

Cell growth can become so rapid that the lumen may become partially or completely obliterated - posing the need to restore the lumen

If it’s unsuccessful can lead to:

  • Stenosis; narrowing of the lumen
  • Atresia; lumen obliterated `
22
Q

What is the most common cause of Upper and lower duodenum atresia?

A

Upper: failure of recanalization
Lower: vascular accident

23
Q

What is gastroschisis?

A

A defect in the anterior abdominal wall (fails to close), gut tube and derivatives are outside body cavity

24
Q

What is omphalocele?

A

Persistence of a physiological herniation: SI comes out of the umbilicus

25
Q

What structure is responsible for cloacal partitioning and what is the result?

A

The urorectal septum provides an anteroposterior division, forming the urogenital sinus and anorectal canal

26
Q

What is an imperforate anus and anorectal agenesis?

A

Imperforate anus: failure of anal membrane to rupture

Anorectal agenesis: high blind-ending rectum, absence of anus and anal canal

27
Q

What structures have a fused mesentery?

A

duodenum, ascending and descending colon, rectum