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Digestive System > Development of the Gut > Flashcards

Development of the Gut Flashcards

1
Q

Foregut goes from

A

pharynx to proximal 1/2 duodenum

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2
Q

midgut goes from

A

distal 1/2 duodenum to proximal 2/3 transverse colon

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3
Q

Hindgut goes from

A

distal 1/3 transverse colon to proximal 2/3 anal canal

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4
Q

How do we start off life?

A

bi-laminar disc of epiblast and hypoblast

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5
Q

Epiblast becomes

A

ectoderm

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6
Q

hypoblast becomes

A

endoderm

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7
Q

What creates the third layer between ectoderm and endoderm

A

mesoderm

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8
Q

oropharangeal membrane

A

eventually forms the mouth. At the cranial end. Ectoderm of the stomodeum. Rupture ~week 4

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9
Q

what does ectoderm become?

A

Anything skin

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10
Q

endoderm

A

the gut tract/ anything mucosa

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11
Q

mesoderm

A

blood vessels/nerves

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12
Q

What is mesenchyme?

A

undifferentiated stem cells

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13
Q

What are the two types of folding in the gut?

A

Longitudinal and transverse

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14
Q

Transverse folding

A

ectoderm and mesoderm fold laterally and ventrally, which close off endoderm forming a seperate gut tube layer.
endoderm > epithelial lining
mesoderm > supporting structures and SM
outer mesenchymal layer > outer tissue layer

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15
Q

Longitudinal Folding

A

~17-18 days. opening between gut tube and yolk sac draws closed like a drawstring bag.
Divides into foregut, midgut (open to yolk sac) and hindgut
With further folding yolk sac opening gets smaller and smaller and gut sections become more defined.

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16
Q

What are the two transitional regions between endoderm (mucosal) and ectoderm (skin)?

A 
oropharangeal membrane (mouth)
anal membrane (anys)
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17
Q

anal membrane

A

Eventually forms the anus. At the caudal end, ectoderm of the anal pit. ~ week 8 ruptures.

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18
Q

What is weird about the development of the gut tube lumen?

A

Initially the gut tube = oatent
As epithelium proliferates, it plugs up the lumen.
~ week 8 recanalization occurs

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19
Q

Arterial supply to FOREGUT

A

Celiac Trunk located @ T12

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20
Q

Arterial supply to MIDGUT

A

Superior Mesenteric Artery @ L1

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21
Q

Arterial supply to HINDGUT

A

Inferior Mesenteric Artery @ L3

22
Q

Whats interesting about SMA

A

It goes all the way through the yolk sac and maintains a connection with the umbilical system

23
Q

Why is the arterial supply of value?

A

Because it indicates the lymphatics and veins

24
Q

Is the lungs endoderm or ectoderm, and why?

A

Endoderm. Because everything that secretes mucus is from endodermal origin.

25
Q

How are the lungs formed?

A

Via a respiratory divaticulum, where the lungs bud of the oesophagus, eventually separating.

26
Q

Oesophagus formation?

A

Starts as small tube immediately caudal to pharynx.
seperates from trachea to form oesophagus.
Rapidly elongates downwards.

27
Q

What are some forms of oesophagus congenital malformations?

A

1) Tracheoesophageal Fistula (abnormal connection) = ‘punches its way into trachea
2) Tracheoesophageal Atresia (blockage) = end up with blind end, baby starts vomiting up milk
3) Congenital Hiatal hernia= short oesophagus, stomach herniates into thorax, through oesophageal hiatus

28
Q

What does the stomach sit between

A

Ventral and dorsal mesogastrium

29
Q

Stage 1 of stomach formation

A

Gut tube starts to dilate

30
Q

Stage 2 of stomach formation

A
  • Dilation cont.
  • rotation on long axis ~90 degrees clockwise
  • Ventral mesogastrium moves to right
  • dorsal mesogastrium moves left
31
Q

Stage 3 of stomach formation

A
  • Dilation cont.
  • rotation on coronal axis ~90 degrees clockwise
  • Right boundary becomes superior (lesser curvature)
  • Left boundary becomes inferior (greater curvature)
32
Q

Omentum is?

A

Two double-sided sheets of peritoneum (4 layers). Extend from each curvature of the stomach

33
Q

Formation of the greater omentum?

A

Dorsal mesogastrium is dragged around to the left due to stomach rotation. Begins to hang down due to WOG.
Both sides of the hanging fold fuse to make 4 layered periotneal structure

34
Q

How can you go from intraperitoneal to retroperitoneal

A

Sometimes some viscera start off as intraperitoneal and then get pushed up against the body wall & the dorsal peritoneal layer gets obliterated.

35
Q

What is the transverse colon intimately fused with?

A

The greater omentum

36
Q

Congenital malformations of the stomach?

A

Congenital hypertrophic Pyloric Stenosis

  • marked thickening of the muscular wall of the pylorus
  • blocks exits from stomach > duodenum
  • attempts to empty stomach spasming and vomiting occurs
37
Q

How can you identify congenital hypertrophic pyloric stenosis?

A

Non-bilious vomit (SI blocked)

38
Q

Are the liver and biliary tree part of the main GI tract?

A

No they come from the ‘hepatic diverticulum’, a ventral outgrowth that occurs ~ week 4.
Divides into 2
Larger, cranial= liver
Smaller, caudal= biliary apparatus

39
Q

How does the bile duct position change?

A

Starts attached to ventral duodenum. As the duodenum grows/rotates it becomes dorsal

40
Q

Formation of the Pancreas?

A

Caudal foregut, develops between both mesogastrium
- 2 buds (major= dorsal, smaller= ventral)
-ventral carried around as duodenum rotates, fuses and anastamoses with dorsal
Pancreatic duct = ventral + dorsal
But the main biliary system is connected via ventral duct / head of pancreas

41
Q

How many still have the accessory duct

A

9%

42
Q

Where are the gastrolienal and lienorenal ligaments found?

A

Stomach (gastrolienal) spleen (lienorenal) kidneys

43
Q

The liver splits the ventral mesogastrium into two, what are they?

A 
Falciform ligament (blood vessels and umbilival veins)
lesser omentum
44
Q

Interesting about the spleen?

A

It is not part of the foregut, it just forms in the dorsal mesogastrium

45
Q

Midgut Formation

A

Starts straight

  • forms U-shaped loop around SMA (cranial and caudal limbs)
  • Herniates into umbilical cord (pysiological)
  • Loop begins to rotate anticlockwise, for 270 degrees
  • Eventually herniation returns and retracts to abdominal cavity.
  • caecum & appendix rotate down to lower abdomen
46
Q

Midgut examples of congenital malformations?

A

1) Non-rotation events
2) Umbilical Hernia/fistula - umbilical cord fails to close properly, gut herniates through weakened region in body wall (gut on outside)
3) Meckel’s Diverticulum
Ileal diverticulum doesn’t pinch off, common (2%), remnant of the yolk stalk (vitelline duct)

47
Q

Hindgut formation

A

Starts as general expanded distal area ‘cloaca’
-this is divided into dorsal and ventral parts by mesenchymal unorectal septum
-As septum grows it seperates the ‘rectum’ from the ‘urogenital sinus’
-

48
Q

Rectal/anal canal?

A

boundary between outer ectoderm and inner endoderm
Pectinate line shows boundary.
upper 2/3 IMA
lower 1/3 systemic circuit
The portal systemic anastomosis (venous drainage goes to two different sites!)

49
Q

Where do anal columns terminate?

A

At site of anal membrane

50
Q

When do anal lymphatics change

A

Anocutaneous line white line)

Below this is SF inguinal nodes

51
Q

Congenital Malformations of the Hindgut

A

1) Megacolon
- segment of colon dilates, due to absense of ANS ganglion cells in the wall of gut distal to it. No nervous innervation= no peristalsis= blockage.
- normally close to anus

2) Imperforated Anus
- failure of anal membrane to rupture

3) Rectal Atresia
- anal canal (blind end) separated from rectum
- fistulas may be present into urogenital system

(MORE COMMON IN MALES)

52
Q

what lies in the lienorenal lig?

A

tail of pancreas and splenic vessels

Digestive System (27 decks)

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