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GI / Hepatology > 13 - GI Embryology > Flashcards

13 - GI Embryology Flashcards

1
Q

Primitive Gut

A

Forms during 4th week of development

Extends from Buccopharyngeal Membrane (rostral) to Cloacal Membrane (caudal)

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2
Q

Why does the gut fold?

A

Dorsal surface grows faster than the ventral surface.

This causes the Buccopharyngeal Membrane and Cloacal Membrane to move towards each other.

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3
Q

Cardiogenic Mesenchyme and Septum Transversum

A

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

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

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4
Q

After folding,

A

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

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5
Q

Cephalocaudal and Lateral folding

A

Occur simultaneously.

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

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6
Q

Midgut remains open until

A

Week 6.

It connects to the yolk sac via vitelline duct.

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7
Q

Buccopharyngeal membrane opens at

A

4 weeks

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8
Q

Cloacal membrane opens at

A

7 weeks

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9
Q

What delimits the bowel?

A

Flexion of the embryo

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10
Q

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

A

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

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11
Q

Septum Transversum

A

Partially separates thoracic and abdominal cavities

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12
Q

Septum Transversum - Superior Portion

A

Primitive pericardial cavity

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13
Q

Septum Transversum - Inferior Portion

A

Future peritoneal cavity

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14
Q

Communication between pericardial and peritoneal cavities

A

Pericardioperitoneal canals

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15
Q

Pericardioperitoneal canals are closed by

A

Formation of the pleuroperitoneal membranes

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16
Q

Pleuroperitoneal membranes

A

Close pericardioperitoneal canals

Contribute muscle to the definitive diaphragm

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17
Q

Definitive Diaphragm

A 
Composite Structure:
Septum Transversum
Pleuroperitoneal Membranes
Paraxial Mesoderm
Esophageal Mesenchyme
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18
Q

Dorsal mesentary

A

Thins to allow the cut to be flexibly suspended

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19
Q

Endoderm

A

Lining of the gut

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

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20
Q

Boundaries between regions

A

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

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21
Q

Boundaries of GI Regions

A

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.

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22
Q

Wnt Signaling - Intestinal Epithelium

A

WNT = Intestine

No WNT = Stomach

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23
Q

Mesenchyme of stomach

A

Expresses Barx1

Secretes WNT inhibitors (sFRP1, 2)

24
Q

Mesenchyme of intestine

A

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

25
Q

Foregut

A

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

26
Q

Foregut derivatives

A 
Pharynx and its derivatives
Lower respiratory tract
Esophagus
Stomach
Duodenum proximal to the ampulla of Vater
Liver
Biliary Apparatus
Pancreas
27
Q

Esophagus - Development

A

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
Q

Stomach - Development

A

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

29
Q

Polyhydramnios

A

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
Q

Stomach rotates

A

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

31
Q

Greater curvature of the stomach

A

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

32
Q

Lesser Sac

A

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
Q

From the duodenum arises

A

Liver
Biliary System
Pancreas

34
Q

Ventral pancreatic bud

A

Rotates around and joins the dorsal pancreatic bud

They fuse to form the pancreas

35
Q

Hepatic diverticulum

A

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
Q

Bare Area of the Liver

A

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

37
Q

Ligaments attached to the liver

A

Falciform ligament
Hepatogastric ligament
Hepatoduodenal ligament

38
Q

Ventral mesogastrium

A

Supports liver and stomach

39
Q

Pancreas is shaped by

A

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
Q

Aberrant rotation can lead to

A

Annular pancreas

41
Q

Annular pancreas

A

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
Q

Midgut

A

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
Q

Derivatives of the midgut

A

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

44
Q

Rotation of the midgut

A

Cranial and caudal loop form
Cranial growth&raquo_space;> 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
Q

Loops of bowel

A

Fuse with the body wall

Become secondarily retroperitoneal

46
Q

Retroperitoneal viscera

A

Thoracic esophagus

Rectum

47
Q

Secondarily retroperitoneal viscera

A 
Ascending colon
Descending colon
Pancreas
Duodenum
Part of the transverse colon?
48
Q

Volvulus

A

Serious complication of excessive flexibility.

Twists around itself, cuts off blood, infarcts.

49
Q

Meckel’s Diverticulum

A

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
Q

Vitelline Duct

A

MUST be obliterated.

51
Q

Hindgut

A

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

52
Q

Derivatives of the hindgut

A

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
Q

Urorectal septum

A

Divides cloaca into rectum and urogenital sinus.

54
Q

Anal Pit

A

Recanalization of cloacal membrane

55
Q

Pectinate line

A

Where anal pit used to be.

56
Q

Proctodeum

A

Forms lower 1/3 of the rectum

The upper 2/3 are formed by the hindgut.

57
Q

Anorectal malformations

A

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

GI / Hepatology (28 decks)

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