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GI tract > Development of the gut > Flashcards

Development of the gut Flashcards

1
Q

What are the divisions of the lateral plate of the mesoderm?

A
  • Somatic - develops into the abdominal wall
  • Splanchnic - develops into smooth muscles of gut wall
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2
Q

Which parts of the trilaminar disc are involved in the development of the GI tract?

A
  • Endoderm - forms internal epithelial lining of GI tract
  • Mesoderm - splits into 2 layers
  • This creates a space known as the coelomic cavity
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3
Q

When does development of the primitive gut tube begin?

A
  • Week 4
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4
Q

Which bits of the GI tract are in the foregut?

A
  • Oesophagus
  • Stomach
  • Duodenum
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5
Q

Which bits of the GI tract are in the midgut?

A
  • Duodenum
  • Jejunum
  • Ileum
  • Ascending colon
  • Distal 2/3 transverse colon
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6
Q

Which bits of the GI tract are in the hindgut?

A
  • Distal 2/3 transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
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7
Q

How does the trilaminar disc form in the 4th week of development?

A
  • Lateral folding
  • This creates a ventral body wall and a tubular primitive gut
  • Cranio-caudal folding
  • This creates the cranial and caudal blind end pouches from yolk sac endoderm.
  • i.e. there is no hole for the mouth or anus yet
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8
Q

What is the gut tube?

A
  • Lined with endoderm
  • Has blind pouches at the head and tail ends
  • Opens at umbilicus via Vitelline duct
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9
Q

Where do the different divisions of the gut develop from?

A
  • Foregut + hindgut develop from head and tail blind pouches
  • Midgut develops from Vitelline duct
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10
Q

What is the intraembryonic coelom?

A
  • A cavity in the centre of the embryo
  • Forms the thoracic and abdominal cavities
  • Cavities are lined by serous membrane
  • This is the peritoneum in the abdomen
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11
Q

Which embryonic structure forms the viscera of the abdominal cavity?

A
  • Splanchnopleuric mesoderm
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12
Q

What is a mesentery?

A
  • Double fold of peritoneum
  • Suspends gut tube within intraembryonic coelom away from abdominal wall
  • Allows for gut tube motility
  • Provides a path for blood and nerve supply from abdominal wall to gut tube
  • Form as a continuation of the mesoderm
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13
Q

Which blood vessels supply the gut?

A
  • Foregut - coeliac artery
  • Midgut - superior mesenteric artery
  • Hindgut - inferior mesenteric artery
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14
Q

What happens to the gut tube in the 5th week of development?

A
  • Endoderm proliferates
  • Occludes lumen of gut tube
  • This recanalises in the 9th week
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15
Q

When does the tracheoesophageal septum form?

A
  • Week 4
  • Trachea sits anteriorly and oesophagus sits posteriorly
  • Lung bud forms ventrally off of foregut
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16
Q

How does the stomach form?

A
  • As a dilation in the foregut
  • Rotates longitudinally 90o anticlockwise
  • Dorsal edge swings left and becomes greater curve
  • Ventral edge swings right and becomes lesser curve
  • Greater curve grows faster than lesser curve
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17
Q

What are the two mesenteries attached to the gut tube?

A
  • Dorsal mesentery
  • Ventral mesentery
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18
Q

Where is the dorsal mesentery found?

A
  • Attaches the back of the gut tube to the posterior abdominal wall.
  • Runs the whole length of the gut tube
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19
Q

Where is the ventral mesentery found?

A
  • Attaches the front of the gut tube to the anterior abdominal wall
  • Only attaches the foregut
  • Leaves a free edge at the end of the foregut
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20
Q

What forms the greater and lesser sacs of the GI tract?

A
  • Dorsal and ventral mesenteries divide the intraembryonic coelom into 2 sections: the left and right sac.
  • Left sac develops into greater sac
  • Right sac develops into lesser sac
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21
Q

Where do the liver and spleen grow from?

A
  • Liver grows in ventral mesentery
  • develops from anterior bud of foregut
  • Spleen grows in dorsal mesentery
22
Q

Is there a connection between the greater and lesser sac of the abdomen?

A
  • Yes - the epiploic foramen or foramen of Winslow
23
Q

What are omenta?

A
  • Sheets of visceral peritoneum
  • Extend from stomach and duodenum
  • Form boundaries of greater and lesser sacs
24
Q

Describe the structure of the greater omentum

A
  • 4 layers of visceral peritoneum
  • attaches to greater curvature of stomach and transverse colon
  • prevents adhesion of organs to parietal peritoneum
  • covers inflamed organs to protect nearby structures
25
Q

Describe the structure of the lesser omentum

A
  • 2 layers of visceral peritoneum
  • attaches to lesser curvature of stomach and liver
  • has a free edge which conducts bile duct, portal vein, and hepatic artery to the liver.
26
Q

What are the peritoneal ligaments?

A

From anterior to posterior:
- Falciform ligament (liver)
- Lesser omentum (stomach)
- Gastrosplenic ligament (spleen)
- Spleno-renal ligament (left kidney)

27
Q

Outline how the pancreas develops

A
  • Develops in 2 buds - one in ventral mesentery and one in dorsal mesentery
  • Ventral bud rotates so that it lies inferior to dorsal bud
  • Buds then fuse to become one gland
28
Q

Where does the midgut begin?

A
  • At the midpoint of the second part of the duodenum
  • Where common bile duct and major pancreatic duct enter duodenum
29
Q

When does herniation of the midgut occur?

A
  • During 6th week of development
30
Q

Why does the midgut herniate?

A
  • Intestinal loop of midgut elongates rapidly
  • Liver is also growing rapidly
  • Abdominal cavity doesn’t grow at the same rate
  • There isn’t enough room for both of these viscera to develop.
  • Intestinal loop herniates out through umbilical cord to create space.
31
Q

What important structure is the axis of the loop of intestine that herniates out of the abdominal cavity?

A
  • Superior mesenteric artery
32
Q

What happens to the loop of intestine after it herniates out of the abdominal cavity?

A
  • It makes 3x 90o turns anticlockwise
  • This moves the small intestine to the left of the large intestine
  • Between 2nd and 3rd rotation, caecum descends to normal location in right iliac fossa
  • Then intestine returns into abdominal cavity at week 10 of development
33
Q

What is incomplete rotation of the midgut?

A
  • Only 1x 90o rotation occurs
  • Left-sided colon
34
Q

What is reversed rotation of the midgut?

A
  • 1x 90o rotation occurs clockwise
  • Transverse colon sits posterior to small intestine
35
Q

What is recanalisation of the gut?

A
  • Growth of intestine is so rapid that the lumen can become partially or completely occluded.
  • Recanalisation restores the lumen
36
Q

What is omphalocoele?

A
  • Herniated contents of midgut remain within umbilical cord when baby is born
  • Midgut contents still covered with peritoneum so still develop relatively normally
  • Mortality is high due to associated genetic defects
37
Q

What is gastroschisis?

A
  • Abdominal wall fails to form anteriorly
  • Intestine and other organs herniate through abdominal wall
  • No peritoneal covering
  • Amniotic fluid negatively affects gut development
  • Mortality rate lower than omphalocoele due to less associated genetic defects
38
Q

What causes vitelline duct abnormalities?

A
  • When vitelline duct does not fully obliterate
  • Can cause vitelline cysts or fistulae
  • Meckel’s diverticulum
39
Q

What is Meckel’s diverticulum?

A
  • Outpouching of gut where vitelline duct hasn’t fully obliterated
  • Like an appendix of small bowel
40
Q

What is the rule of 2s?

A

Meckel’s diverticulum:
- Affects 2% of population
- Is located 2 feet from the ileocecal valve
- Detected in under 2s
- Affects 2x more men than women

41
Q

What happens if recanalisation of the midgut is unsuccessful?

A
  • Atresia (complete closure) or stenosis (narrowing) can occur
  • Often affects duodenum
42
Q

What supplies the hindgut?

A
  • Inferior mesenteric artery
  • Least splanchnic nerve (T12)
  • Pain in the hindgut localises to the suprapubic region
43
Q

What is the cloacal membrane?

A
  • Covers the hindgut during development
  • Ruptures in week 7, opening up anorectal canal to amniotic fluid
44
Q

What is the cloaca?

A
  • The name given to the hindgut that communicates with the developing genitourinary tract
  • Area where ectoderm meets endoderm without any dividing mesoderm
45
Q

What is the role of the urorectal septum?

A
  • Wedge of mesoderm
  • Descends caudally during weeks 4-7
  • Separates cloaca into urogenital sinus and anorectal canal
46
Q

What divides the anal canal into sections?

A
  • Pectinate line
  • This is the point where endoderm and ectoderm met suring development
47
Q

Describe the anal canal above the pectinate line

A
  • Anal canal developed from endoderm
  • Supplied by inferior mesenteric artery and least splanchnic nerve (T12)
  • Vague pain due to stretch
  • Non-keratinised
48
Q

Describe the anal canal below the pectinate line

A
  • ## Anal canal derived from ectoderm
48
Q

Describe the anal canal below the pectinate line

A
  • Anal canal derived from ectoderm
  • Supplied by pudendal artery and pudendal nerve
  • Localised pain
  • Keratinised
49
Q

What are some hindgut abnormalities?

A
  • Imperforate anus - failure to rupture anal membrane
  • Anorectal agenesis - anus doesn’t form
  • Fistulae between rectum and anus

GI tract (23 decks)

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