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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
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

GI / Hepatology (28 decks)

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