13 - GI Embryology Flashcards Preview

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Flashcards in 13 - GI Embryology Deck (57)
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

31

Greater curvature of the stomach

Previously dorsal, then becomes right (false?). Grows faster than lesser curvature.

32

Lesser Sac

Dorsal mesograstrium moves to the left.
Ventral mesogastrium attaches to liver and body wall.
Inferior recess forms the greater omentum.
Layers fuse to obliterate the lesser sac.

33

From the duodenum arises

Liver
Biliary System
Pancreas

34

Ventral pancreatic bud

Rotates around and joins the dorsal pancreatic bud
They fuse to form the pancreas

35

Hepatic diverticulum

Grows from the duodenum into the ventral mesentery (Week 4)
Divides into cranial and caudal buds
Cranial bud grows faster (becomes hepatic parenchyma)
Hematopoietic colonists arrive ~ week 6
Caudal bud gives rise to the biliary system.

36

Bare Area of the Liver

Liver presses against septum transversum, eliminating ventral mesentary on that part.

37

Ligaments attached to the liver

Falciform ligament
Hepatogastric ligament
Hepatoduodenal ligament

38

Ventral mesogastrium

Supports liver and stomach

39

Pancreas is shaped by

Rotation of the stomach

Cardiogenic mesenchyme induces ventral pancreatic bud (home of the main duct) to form.
Notochord induces dorsal pancreatic bud (most of the pancreas) to form.
Rotation combines the two.

40

Aberrant rotation can lead to

Annular pancreas

41

Annular pancreas

Ring around the duodenum
Not a problem as a fetus
As the duodenum grows, the pancreas gets cut off!!

It's like pyloric stenosis but PLUS DIGESTING YOURSELF!!!!!!

42

Midgut

All are supplied by the superior mesenteric artery
Grows rapidly
Herniates into the umbilical cord
Rotates around an axis of the SMA 90 degrees
Herniation comes back in
Rotates around the SMA 180 degrees!

43

Derivatives of the midgut

Small intestine (except proximal duodenum)
Cecum
Appendix
Ascending colon
Right 1/2 to 2/3 of the proximal transverse colon.

44

Rotation of the midgut

Cranial and caudal loop form
Cranial growth >>> caudal growth
Apex of the loop is the vitelline duct
Cranial loop moves to the right, caudal loop moves to the left (90 degrees counterclockwise)
Reduction of midgut hernia
180 degrees further rotation
Brings cecum to the right, moves down, becomes secondarily retroperitoneal.

45

Loops of bowel

Fuse with the body wall
Become secondarily retroperitoneal

46

Retroperitoneal viscera

Thoracic esophagus
Rectum

47

Secondarily retroperitoneal viscera

Ascending colon
Descending colon
Pancreas
Duodenum
Part of the transverse colon?

48

Volvulus

Serious complication of excessive flexibility.
Twists around itself, cuts off blood, infarcts.

49

Meckel's Diverticulum

Bad news
Diverticulum near vitelline duct
Pluripotent cells. Can lead to inappropriately-located tissue. DIGEST YOURSELF GURL

Can lead to omphallomesenteric fistulas, cysts or ligaments.

50

Vitelline Duct

MUST be obliterated.

51

Hindgut

Supplied by the inferior mesenteric artery
Originally a cloaca
Partitioned to form rectum and urogenital sinus (forming bladder, ureters & urethra)

52

Derivatives of the hindgut

Left 1/3 to 1/2 of the distal transverse colon
Descending colon
Sigmoid colon
Rectum
Superior part of the anal canal
Epithelium of urinary bladder and most of urethra.

53

Urorectal septum

Divides cloaca into rectum and urogenital sinus.

54

Anal Pit

Recanalization of cloacal membrane

55

Pectinate line

Where anal pit used to be.

56

Proctodeum

Forms lower 1/3 of the rectum
The upper 2/3 are formed by the hindgut.

57

Anorectal malformations

Fistula between rectum and scrotum
Rectal atresia
Fistula between rectum and urethra
Fistula between rectum and vagina