13 - GI Embryology Flashcards Preview

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Flashcards in 13 - GI Embryology Deck (57)
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1

Primitive Gut

Forms during 4th week of development
Extends from Buccopharyngeal Membrane (rostral) to Cloacal Membrane (caudal)

2

Why does the gut fold?

Dorsal surface grows faster than the ventral surface.
This causes the Buccopharyngeal Membrane and Cloacal Membrane to move towards each other.

3

Cardiogenic Mesenchyme and Septum Transversum

Originally rostral
Folding brings it caudally, ending up caudal to the buccopharyngeal membrane

At this point, the primitive gut is sort of recognizable.

4

After folding,

A portion of the yolk sac is incorporated into the embryo as bowel, but the midgut remains open

5

Cephalocaudal and Lateral folding

Occur simultaneously.

Meeting and fusion of cranial, lateral and caudal edges of the embryo create the primordial foregut and hindgut.

6

Midgut remains open until

Week 6.

It connects to the yolk sac via vitelline duct.

7

Buccopharyngeal membrane opens at

4 weeks

8

Cloacal membrane opens at

7 weeks

9

What delimits the bowel?

Flexion of the embryo

10

After the gut forms - Attached to the body wall how?

Via dorsal and ventral mesentaries. Ventral mesentary is lost except in the region of the liver.
Vitelline duct remains in the umbilical cord.

11

Septum Transversum

Partially separates thoracic and abdominal cavities

12

Septum Transversum - Superior Portion

Primitive pericardial cavity

13

Septum Transversum - Inferior Portion

Future peritoneal cavity

14

Communication between pericardial and peritoneal cavities

Pericardioperitoneal canals

15

Pericardioperitoneal canals are closed by

Formation of the pleuroperitoneal membranes

16

Pleuroperitoneal membranes

Close pericardioperitoneal canals
Contribute muscle to the definitive diaphragm

17

Definitive Diaphragm

Composite Structure:
Septum Transversum
Pleuroperitoneal Membranes
Paraxial Mesoderm
Esophageal Mesenchyme

18

Dorsal mesentary

Thins to allow the cut to be flexibly suspended

19

Endoderm

Lining of the gut
Specified (via a series of regionally specific transcription factors) before gut tube is complete

20

Boundaries between regions

Plastic
Depend on interactions between endoderm & mesoderm
Language: Paracrine secretion of growth factors

21

Boundaries of GI Regions

Begin with Sonic HedgeHog expression in posterior endoderm, which spreads to the whole gut.
Induces a series of Hox genes in the mesoderm
Mesoderm then influences epithelial differentiation.

22

Wnt Signaling - Intestinal Epithelium

WNT = Intestine
No WNT = Stomach

23

Mesenchyme of stomach

Expresses Barx1
Secretes WNT inhibitors (sFRP1, 2)

24

Mesenchyme of intestine

Secretes BMP4
Induces mesenchyme anterior to it to express SOX9 + NKX-2
Becomes pyloric sphincter

25

Foregut

Part of the bowel from the stomach to the biliary apparatus, all are supplied by the celiac artery.

26

Foregut derivatives

Pharynx and its derivatives
Lower respiratory tract
Esophagus
Stomach
Duodenum proximal to the ampulla of Vater
Liver
Biliary Apparatus
Pancreas

27

Esophagus - Development

Elongates rapidly
Grows faster at the cranial end
Epithelium obliterates lumen
Week 8 - Esophagus recanalized by apoptosis.
Failure at this step causes polyhydramnios, esophageal atresia or tracheo-esophageal fistula

28

Stomach - Development

Does not descend. Arises from region just caudal to septum transversum.
Then stomach enlarges and rotates.

29

Polyhydramnios

Pregnant woman's abdoman extends
Heart sounds faint
Clue to esophagus not being recanalised
Does not prevent development. Baby looks normal.
Baby aspirates upon first feeding. Lipid pneumonia. BAD NEWS

30

Stomach rotates

90 degrees Clockwise
Creates the lesser sac
Facilitated by vacuolization and apoptosis