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GI System > Embryology of the GI Tract > Flashcards

Embryology of the GI Tract Flashcards

1
Q

What is gastrulation?

A

Formation of the trilaminar disc:

Ectoderm, endoderm & mesoderm

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2
Q

What occurs in week 1?

A

Fertilisation and implantation

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3
Q

What occurs in week 2?

A

Bilaminar disc formation

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4
Q

What occurs in week 2-3?

A

Establishment of body axes (anterior-posterior/left-right) due to gene expression

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5
Q

What occurs in week 3?

A

Gastrulation: bilaminar disc –> trilaminar disc

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6
Q

What occurs in week 3-8?

A

Organogenesis (formation of organs)

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7
Q

In what week does the primordial gut tube form and from what layer?

A

4th week and from the endoderm lining the yolk sac

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8
Q

What two membranes close the ends of the primordial gut tube?

A

Cranial end: oropharyngeal membrane

Caudal end: cloacal membrane

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9
Q

Where does the oeosophagus form from?

A

Cranial end of the primitive tube. The trachea-oesophageal septum (ridge) divide the foregut into the trachea and oesophagus

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10
Q

In what week does the stomach form?

A

4th week, the foregut dilates to form stomach

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11
Q

What causes the stomach to form a lesser and greater curvature?

A

Differential growth rates

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12
Q

What two rotations does the stomach undergo?

A

Longitudinal

Anterio-posterior

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13
Q

Describe the longitudinal rotation the stomach

A

90 degree rotation so that the ventral border now lies on the left side (LC) and the dorsal border now on the right (GC) - faces different direction

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14
Q

Describe anterio-posterior rotation of the stomach

A

Creates final position: tilts backwards so that LC is superior to GC

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15
Q

How is the omental bursa (lesser sac) created?

A

Mesogastrium (mesentery connecting stomach to body walls) repositioned during stomach rotation.

Longitudinal rotation pulls dorsal mesentery to the LEFT to create the omental bursa (and ventral mesogastrium pulled to right)

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16
Q

From which part of the gut tube is the duodenum formed from?

A

Caudal part of foregut and cranial part of the midgut

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17
Q

How is the duodenum peritonised?

A

The 1st part is intraperitoneal as the duodenal cap retains its dorsal mesentery, but the rest of the duodenum is retroperitoneal as its mesentery fuses with the peritoneum of the posterior abdominal wall

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18
Q

When does the liver primordial bud begin to develop and from what layer?

A

In the 3rd week as an outgrowth of endoderm in the distal end of the foregut

It grows into the septum transverse (primitive diaphragm)

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19
Q

How does the bile duct, Gallbladder and cystic duct form?

A

Connection between liver bud and foregut (duodenum) narrows to form the bile duct.

Ventral outgrowth from the bile duct forms the gall badder and cystic duct

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20
Q

When does the spleen begin to develop and how?

A

Mesenchymal condensation in the dorsal mesogastrium (L side of body) but develops in the 5th week when the mesenchyme differentiates

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21
Q

What is mesenchyme?

A

Mesodermal embryonic tissue which develops into connective and skeletal tissues, including blood and lymph (forms spleen)

22
Q

What is the role of the spleen in weeks 14, 15-7 and 23?

A

W14: haematopoietic organ (producing blood cells)

W15-17: becomes lobular and colonised by T-lymphocytes

W23: development of B-cell precursors and spleen begins lymphoid function

23
Q

In what week does the pancreas develop and from what layer?

A

In week 5 from two buds:
Ventral (which outgrows from the bile duct
Dorsal from the duodenum

24
Q

How does the pancreas develop?

A

As duodenum rotates (due to stomach repositioning) the ventral bud moves to lie directly below the dorsal bud.

25
Q

How does the main pancreatic duct form?

A

The ventral and dorsal buds fuse, with the ventral + distal part of dorsal duct forming MPD.

The proximal part of the dorsal duct forms an accessory duct.

26
Q

What structures are found in the midgut?

A 
Distal part of duodenum 
Jejunum
Ileum 
Appendix
Caecum
Ascending colon 
2/3 transverse colon
27
Q

What is the primary intestinal loop?

A

Part of the midgut, after rapid elongation of the gut tube and mesentery

28
Q

What does the cephalic part of the primary intestinal loop become?

A

Distal duodenum, jejenum and proximal ileum

29
Q

What does the caudal part of the primary intestinal loop become?

A

Distal ileum, caecum, appendix, ascending colon and proximal 2/3 of transverse colon

30
Q

What two movements must the primary intestinal loop undergo to reach adult pattern?

A

Rotation and herniation

31
Q

How does rotation of the primary intestinal loop occur?

A

Rotates around the axis of the superior mesenteric artery (cranial part shifted to the right side of abdomen- goes under the caudal part) - 90 degrees anticlockwise

32
Q

In what week does rotation of the primary intestinal loop occur?

A

6th week

33
Q

Describe the process of herniation of the primary intestinal loop

A

As 90 rotation occurs, the gut tube herniates into the extra embryonic cavity in the umbilical cord

Retraction occurs in the 10th week (as abdominal cavity becomes more spacious) and as the loops move back into the abdomen, there is a further 180 degree rotation anti-clockwise

34
Q

What does the hindgut consist of?

A

Distal 1/3 transverse colon, descending colon, sigmoid colon, rectum and upper part of anal canal

35
Q

What embryonic layer forms the urethra and bladder?

A

Endoderm of the hindgut

36
Q

What is the primitive anal canal called?

A

Cloaca

37
Q

What embryonic layers is the cloaca derived from?

A

It is an endoderm lined cavity, however the clocal membrane (at the ventral surface of cloacal on body wall) is ectoderm

38
Q

What embryonic layer separates the allantois and hindgut?

A

Mesoderm (becomes the ureorectal septum)

39
Q

What is the primitive urogenital sinus?

A

When the allantois enters into the anterior part of the cloaca

40
Q

What happens in to the clocal membrane in the 7th week?

A

Ruptures, creating an opening for the hindgut

41
Q

How is the anal canal reformed after rupturing of cloacal membrane?

A

Ectoderm of anal canal proliferation closing the caudal end - so causal anal canal is ectoderm derived with a different blood supply

42
Q

In what week does the anal canal reopen?

A

Week 9

43
Q

Name three conditions caused by abnormal development in the foregut

A

Oesophageal atresia
Trachea-oesophageal fistula
Annular pancreas

44
Q

What is annular pancreas?

A

Developmental condition caused by failure of ventral pancreatic bud to migrate around the duodenum correctly (could cause duodenal stenosis)

45
Q

Name three conditions cause by abnormal development of the midgut

A

Omphalocele
Gastrochisis
Remnant of Vitelline Duct

46
Q

What is omphalocele?

A

Herniation of abdominal viscera through enlarge umbilical ring but still covered by layer of amnion - may include liver, stomach, intestinal loops

47
Q

What is gastrochisis?

A

Herniation of abdominal content directly though the body wall into amniotic cavity (no covering) through week area in umbilicus

48
Q

What happens if there are remnants of the Vitelline duct?

A

Forms Meckel’s Diverticulum: remnants of ileum goes into the umbilical cord and stays intact, so faecal matter passes though the umbilicus

49
Q

What abnormal developmental issue causes conditions in the hindgut?

A

Failure of separation of the hindgut from the urogenital sinus by the urorectal septum

50
Q

What conditions arise due to lack of urorectal septum formation?

A

Urorectal fistula
Rectovaginal fistula
Rectoanal atresia
Imperforate anus

GI System (28 decks)

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