8) Development of Midgut and Hindgut Flashcards Preview

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Flashcards in 8) Development of Midgut and Hindgut Deck (41)
1

What is physiological herniation?

Intestines of midgut herniate into umbilical cord to continue development

2

Describe the primary intestinal loop:

Has cranial and caudal limbs with SMA as its axis
Is connected to yolk sac by vitelline duct

3

Why is physiological herniation required?

Growth of primary intestinal loop is rapid
Liver is also growing rapidly and abdominal cavity is too small to accommodate both

4

Describe the midgut rotation:

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

5

Describe the first 90 degree rotation:

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

6

What do the further two rotations ensure?

That cranial limb enters the abdominal cavity first

7

Describe the intestine's return to the cavity:

Cranial limb moves to the left
Caecal bud returns last and then descends to right lower quadrant

8

What are the derivatives of the cranial limb?

Distal duodenum, jejunum, proximal ileum

9

What are the derivatives of the caudal limb?

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

10

What is incomplete rotation of the midgut?

Midgut loop makes only one 90 degree rotation
Results in left-sided colon

11

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

Midgut loop makes one 90 degree rotation clockwise
Means that transverse colon passes posterior to duodenum - so can wrap around and occlude it

12

What is a major complication of midgut defects?

Volvulus - strangulation and ischaemia

13

What abnormalities can a persistent vitelline duct cause?

Vitelline cyst
Vitelline fistula
Meckel's diverticulum

14

What is a vitelline fistula?

Direct communication between umbilicus and intestinal tract

15

What is Meckel's diverticulum?

Cul-de-sac in ileum
Can contain ectopic gastric or pancreatic tissue causing ulceration

16

What structures have their lumens obliterated?

Oesophagus, bile duct, small intestine, duodenum

17

Why is the lumen obliterated?

Cell growth becomes too rapid

18

What process restores obliterated lumen?

Recanalisation

19

What happens if recanalization isn't successful?

Atresia or stenosis

20

Where do most of recanalization failures occur?

Duodenum then jejunum and ileum then colon

21

What causes atresia and stenosis in lower duodenum?

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

22

What can cause a vascular accident?

Malrotation, volvulus, body wall defect

23

Why is a pyloric stenosis and how does it present?

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

24

What is gastroschisis?

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

25

What is omphalocoele (exomphalos)?

Persistence of physiological hernation, covered in amnion

26

What is the end of the hindgut?

Cloaca

27

What divides the cloaca and into what?

Wedge of mesoderm (urorectal septum)
Divides into urogenital sinus and anorectal canal

28

What is the proctodeum?

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

29

What line divides the anal canal?

Pectinate line

30

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

Columnar epithelium
IMA
S2,3,4 pelvic parasympathetic

31

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

Stratified squamous
Pudendal artery
Pudendal nerve (S2-4)

32

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

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

33

Describe visceral pain:

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

34

What is imperforate anus?

Failure of anal membrane to rupture

35

What other hindgut abnormalities are there?

Anal/anorectal agenesis
Hindgut fistulae

36

What midgut and hindgut structures maintain their mesentery?

Jejunum, ileum, appendix, transverse and sigmoid colon

37

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

Duodenum, ascending and descending colon, rectum

38

What does the dorsal mesentery become?

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

39

What does the ventral mesentery become?

Lesser omentum
Falciform ligament

40

What is the blood and nerve supply to midgut?

SMA and SMV
PSNS: vagus
SNS: superior mesenteric plexus

41

What is the blood and nerve supply to hindgut?

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