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Flashcards in Development of the Gut Deck (52):
1

Foregut goes from

pharynx to proximal 1/2 duodenum

2

midgut goes from

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

3

Hindgut goes from

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

4

How do we start off life?

bi-laminar disc of epiblast and hypoblast

5

Epiblast becomes

ectoderm

6

hypoblast becomes

endoderm

7

What creates the third layer between ectoderm and endoderm

mesoderm

8

oropharangeal membrane

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

9

what does ectoderm become?

Anything skin

10

endoderm

the gut tract/ anything mucosa

11

mesoderm

blood vessels/nerves

12

What is mesenchyme?

undifferentiated stem cells

13

What are the two types of folding in the gut?

Longitudinal and transverse

14

Transverse folding

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

15

Longitudinal Folding

~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.

16

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

oropharangeal membrane (mouth)
anal membrane (anys)

17

anal membrane

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

18

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

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

19

Arterial supply to FOREGUT

Celiac Trunk located @ T12

20

Arterial supply to MIDGUT

Superior Mesenteric Artery @ L1

21

Arterial supply to HINDGUT

Inferior Mesenteric Artery @ L3

22

Whats interesting about SMA

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

23

Why is the arterial supply of value?

Because it indicates the lymphatics and veins

24

Is the lungs endoderm or ectoderm, and why?

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

25

How are the lungs formed?

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

26

Oesophagus formation?

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

27

What are some forms of oesophagus congenital malformations?

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

What does the stomach sit between

Ventral and dorsal mesogastrium

29

Stage 1 of stomach formation

Gut tube starts to dilate

30

Stage 2 of stomach formation

-Dilation cont.
- rotation on long axis ~90 degrees clockwise
- Ventral mesogastrium moves to right
-dorsal mesogastrium moves left

31

Stage 3 of stomach formation

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

32

Omentum is?

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

33

Formation of the greater omentum?

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

How can you go from intraperitoneal to retroperitoneal

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

35

What is the transverse colon intimately fused with?

The greater omentum

36

Congenital malformations of the stomach?

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

How can you identify congenital hypertrophic pyloric stenosis?

Non-bilious vomit (SI blocked)

38

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

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

How does the bile duct position change?

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

40

Formation of the Pancreas?

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

How many still have the accessory duct

9%

42

Where are the gastrolienal and lienorenal ligaments found?

Stomach (gastrolienal) spleen (lienorenal) kidneys

43

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

Falciform ligament (blood vessels and umbilival veins)
lesser omentum

44

Interesting about the spleen?

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

45

Midgut Formation

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

Midgut examples of congenital malformations?

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

Hindgut formation

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

Rectal/anal canal?

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

Where do anal columns terminate?

At site of anal membrane

50

When do anal lymphatics change

Anocutaneous line white line)
Below this is SF inguinal nodes

51

Congenital Malformations of the Hindgut

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

what lies in the lienorenal lig?

tail of pancreas and splenic vessels