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13. Gastrointestinal > Embryology 2. Development of the Midgut and Hindgut > Flashcards

Embryology 2. Development of the Midgut and Hindgut Flashcards

1
Q

What are the derivatives of the midgut?

A

Small intestine (including most of the duodenum, post bile duct entry), caecum and appendix, ascending colon, proximal 2/3 of transverse colon.

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2
Q

What causes the primary intestinal loop to form?

A

The midgut elongates enormously but runs out of space due to the large liver, so the midgut loops.

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3
Q

What does the primary intestinal loop form around?

A

Superior mesenteric artery.

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4
Q

What is the primary intestinal loop connected to the yolk sac by?

A

The vitelline duct.

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5
Q

What are the limbs of the midgut primary intestinal loop?

A

Cranial and caudal limbs.

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6
Q

What are the derivatives of the cranial limb of the primary intestinal loop?

A

Distal duodenum, jejunum, proximal ileum.

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7
Q

What are the derivatives of the caudal limb of the primary intestinal loop?

A

Distal ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon.

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8
Q

Why is physiological herniation in the 6th week of development necessary?

A

The abdominal cavity is too small to accommodate both the growing primary loop and the liver, so the intestines herniate into the proximal umbilical cord.

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9
Q

What does the primary loop herniate into in physiological herniation?

A

The proximal umbilical cord, alongside umbilical vessels.

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10
Q

What is the first rotation of the midgut loop?

A

It rotates around the axis (superior mesenteric artery) in an anticlockwise direction.

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11
Q

What is the result of the first midgut loop rotation?

A

The cranial limb moves to the back and the caudal limb to the front.

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12
Q

What is the second rotation of the midgut loop?

A

It turns 90 degrees anticlockwise twice.

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13
Q

What is the overall rotation of the midgut loop?

A

270 degrees in an anticlockwise direction.

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14
Q

Where does the cranial limb end up as a result of rotation?

A

The left hand side.

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15
Q

What happens to the caecum on returning to the abdomen?

A

It descends into the right lower quadrant.

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16
Q

What is the incomplete rotation?

A

The midgut only makes one 90 degree rotation so there is a left sided colon.

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17
Q

What is reversed rotation?

A

The midgut makes one 90 degree clockwise so the transverse colon passes posterior to the duodenum.

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18
Q

What is the result of reversed rotation?

A

The duodenum can wrap around the transverse colon and occlude it. Hypermobile guts may result.

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19
Q

What is a volvulus?

A

A bowel obstruction where a loop of bowel has abnormally twisted in on itself.

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20
Q

What is volvulus formation more likely with?

A

Hypermobile guts.

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21
Q

What can volvulus formation lead to?

A

Strangulation and ischaemia.

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22
Q

What are the derivatives of the hindgut?

A

The distal 1/3 of the transverse colon, descending colon, rectum, superior part of the anal canal, and epithelium of the urinary bladder.

23
Q

What happens at 6 weeks development to the hindgut?

A

It ends in the cloaca and is separated from the outside by the cloacal membrane.

24
Q

What is cloacal partitioning?

A

A wedge of mesoderm grows down into the cloaca, dividing it in to the urogenital sinus anteriorly and the anorectal canal posteriorly.

25
Q

What are the embryonic derivations of the anal canal?

A

Superior part from hindgut. Inferior part from the endoderm.

26
Q

What are the superior and inferior parts of the anal canal separated by?

A

The pectinate line.

27
Q

What is the blood supply to the anal canal?

A

Above pectinate line - inferior mesenteric artery, below - pudendal artery.

28
Q

What is the innervation of the anal canal?

A

Above pectinate line - S2/3/4 pelvic parasympathetic, below - S2/3/4 pudendal nerve.

29
Q

What is the epithelia of the anal canal?

A

Above Pectinate line - columnar, below - stratified squamous.

30
Q

What is the lymph drainage of the anal canal?

A

Above Pectinate line - internal iliac nodes, below - superficial inguinal nodes.

31
Q

What are the sensations of the anal canal?

A

Above the Pectinate line - only stretch, below - temperature, touch, pain due to somatic innervation.

32
Q

What is Meckel’s diverticulum?

A

The most common GI abnormality. It is a cul-de-sac in the ileum.

33
Q

What is the rule of 2s for Meckel’s diverticulum?

A

2% of the population affected, 2 feet from the ileocaecal valve, 2 inches long, detected in under 2s, 2:1 male:female.

34
Q

What can a complication of Meckel’s diverticulum be?

A

It can contain ectopic gastric or pancreatic tissue which will secrete enzymes and acids, causing ulceration.

35
Q

What is a vitelline cycst?

A

The vitelline duct forms fibrous strands at either end.

36
Q

What is a vitelline fistula?

A

A direct communication between the umbilicus and the intestinal tract.

37
Q

What is the result of a vitelline fistula?

A

Faecal matter coming out of the umbilicus.

38
Q

Why is recanalisation of the primitive gut tube needed in some gut structures?

A

The cell growth becomes so rapid that the lumen is partially or completely obliterated.

39
Q

What is the aim of recanalisation?

A

To restore the lumen.

40
Q

What results from failure to recanalise?

A

Atresia - complete loss of the lumen, or stenosis - narrowing of the lumen.

41
Q

Where does most atresia/ stenosis occur in the GI tract?

A

In the duodenum.

42
Q

What are the causes of atresias in the duodenum?

A

Upper duodenum from recanalisation failure, in the lower duodenum from vascular accident.

43
Q

What is a vascular accident causing atresia?

A

Loss of blood supply means part of the gut dies.

44
Q

What is pyloric stenosis?

A

A common abnormality of the stomach in infants. Narrowing of the exit from the stomach causing projectile vomiting.

45
Q

What causes pyloric stenosis?

A

Hypertrophy of the circular muscle in the region of the pyloric sphincter.

46
Q

What is gastroschisis?

A

The failure of closure of the abdominal wall during folding of the embryo, which leaves the gut tube and its derivative outside the body cavity.

47
Q

What is a complication of gastroschisis?

A

The gut tube and derivatives have no covering as they herniate through the abdominal wall directly into the amniotic cavity.

48
Q

What is omphalocoele?

A

The persistence of physiological herniation. Part of the gut tube fails to return to the abdominal cavity following its normal herniation into the umbilical cord.

49
Q

What is imperforate anus?

A

Failure of the anal membrane to rupture.

50
Q

What is anal/anorectal agenesis?

A

Failure of development of the anus or anus and rectum.

51
Q

What is a hindgut fistula?

A

Abnormal connection within the hindgut.

52
Q

What are the mesenteries retained by?

A

Jejunum, ileum, appendix, transverse colon, sigmoid colon.

53
Q

What are the structures of the midgut and hindgut with fused mesenteries?

A

Duodenum, ascending colon, descending colon, and rectum.

13. Gastrointestinal (17 decks)

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