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Gastrointestinal Tract > 8) Development of Midgut and Hindgut > Flashcards

8) Development of Midgut and Hindgut Flashcards

1
Q

What is physiological herniation?

A

Intestines of midgut herniate into umbilical cord to continue development

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2
Q

Describe the primary intestinal loop:

A

Has cranial and caudal limbs with SMA as its axis

Is connected to yolk sac by vitelline duct

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3
Q

Why is physiological herniation required?

A

Growth of primary intestinal loop is rapid

Liver is also growing rapidly and abdominal cavity is too small to accommodate both

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4
Q

Describe the midgut rotation:

A

Rotates in a counter-clockwise direction in a series of 3 ninety degree turns

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5
Q

Describe the first 90 degree rotation:

A

Brings cranial and caudal limbs to same level, small intestine elongation continued forming coiled loops

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6
Q

What do the further two rotations ensure?

A

That cranial limb enters the abdominal cavity first

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7
Q

Describe the intestine’s return to the cavity:

A

Cranial limb moves to the left

Caecal bud returns last and then descends to right lower quadrant

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8
Q

What are the derivatives of the cranial limb?

A

Distal duodenum, jejunum, proximal ileum

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9
Q

What are the derivatives of the caudal limb?

A

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

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10
Q

What is incomplete rotation of the midgut?

A

Midgut loop makes only one 90 degree rotation

Results in left-sided colon

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11
Q

What is reversed rotation of the midgut and what can it lead to?

A

Midgut loop makes one 90 degree rotation clockwise

Means that transverse colon passes posterior to duodenum - so can wrap around and occlude it

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12
Q

What is a major complication of midgut defects?

A

Volvulus - strangulation and ischaemia

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13
Q

What abnormalities can a persistent vitelline duct cause?

A

Vitelline cyst
Vitelline fistula
Meckel’s diverticulum

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14
Q

What is a vitelline fistula?

A

Direct communication between umbilicus and intestinal tract

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15
Q

What is Meckel’s diverticulum?

A

Cul-de-sac in ileum

Can contain ectopic gastric or pancreatic tissue causing ulceration

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16
Q

What structures have their lumens obliterated?

A

Oesophagus, bile duct, small intestine, duodenum

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17
Q

Why is the lumen obliterated?

A

Cell growth becomes too rapid

18
Q

What process restores obliterated lumen?

A

Recanalisation

19
Q

What happens if recanalization isn’t successful?

A

Atresia or stenosis

20
Q

Where do most of recanalization failures occur?

A

Duodenum then jejunum and ileum then colon

21
Q

What causes atresia and stenosis in lower duodenum?

A

Vascular accident, loss of blood supply so part of gut dies

22
Q

What can cause a vascular accident?

A

Malrotation, volvulus, body wall defect

23
Q

Why is a pyloric stenosis and how does it present?

A

Hypertrophy of circular muscle in region of pyloric sphincter
Leads to difficulty empting stomach so projective vomiting

24
Q

What is gastroschisis?

A

Failure of closure of abdominal wall during folding of embryo leaving gut tube outside of body with no covering

25
Q

What is omphalocoele (exomphalos)?

A

Persistence of physiological hernation, covered in amnion

26
Q

What is the end of the hindgut?

A

Cloaca

27
Q

What divides the cloaca and into what?

A

Wedge of mesoderm (urorectal septum)

Divides into urogenital sinus and anorectal canal

28
Q

What is the proctodeum?

A

Anal pit, where ectoderm (inferior) meets endoderm (superior)

29
Q

What line divides the anal canal?

A

Pectinate line

30
Q

What is the epithelium, blood supply and nerve supply above the pectinate line?

A

Columnar epithelium
IMA
S2,3,4 pelvic parasympathetic

31
Q

What is the epithelium, blood supply and nerve supply below the pectinate line?

A

Stratified squamous
Pudendal artery
Pudendal nerve (S2-4)

32
Q

Describe the difference in sensation above and below the pectinate line:

A

Above: sensation is only stretch. Pain is dull and poorly localised
Below: sensation is temp, touch and pain sensitive (well localised)

33
Q

Describe visceral pain:

A

Poorly localised and pattern reflects development of structure:
Foregut - epigastric
Midgut - Periumbilical
Hindgut - Suprapubic

34
Q

What is imperforate anus?

A

Failure of anal membrane to rupture

35
Q

What other hindgut abnormalities are there?

A

Anal/anorectal agenesis

Hindgut fistulae

36
Q

What midgut and hindgut structures maintain their mesentery?

A

Jejunum, ileum, appendix, transverse and sigmoid colon

37
Q

What midgut and hindgut structures have fused mesenteries? (think retroperitoneal)

A

Duodenum, ascending and descending colon, rectum

38
Q

What does the dorsal mesentery become?

A 
Greater momentum
Gastrolineal ligament (stomach to spleen)
Lienorenal ligament (spleen to kidney)
Mesocolon 
Mesentery proper
39
Q

What does the ventral mesentery become?

A

Lesser omentum

Falciform ligament

40
Q

What is the blood and nerve supply to midgut?

A

SMA and SMV
PSNS: vagus
SNS: superior mesenteric plexus

41
Q

What is the blood and nerve supply to hindgut?

A

IMA and IMV
PSNS: pelvic (S2-4)
SNS: inferior mesenteric plexus

Gastrointestinal Tract (11 decks)

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