Embryology 2 Flashcards

1
Q

What is the primary intestinal loop

A

A loop of the midgut that forms because the midgut elongates massively and runs out of space (due to large size of developing liver)

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2
Q

Features of the primary intestinal loop

A

Has the superior mesenteric artery at its axis
Connected to the yolk sac by the vitelline duct
Has a cranial limb (superior to SMA and vitelline duct) and a caudal limb (inferior to SMA and vitelline duct)

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3
Q

Adult derivatives of cranial limb

A

Distal duodenum
Jejunum
Proximal ileum

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4
Q

Adult derivatives of caudal limb

A
Distal ileum
Caecum
Appendix
Ascending colon
Proximal 2/3 transverse colon
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5
Q

What is physiological herniation

A

The intestines herniate into the proximal umbilical cord alongside the umbilical vessels as the abdominal cavity is too small to accommodate the primary intestinal loop and the liver

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6
Q

When does physiological herniation occur

A

Week 6

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7
Q

How much does the midgut rotate overall

A

270 degrees anticlockwise

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8
Q

Where does the first rotation (90 degrees anti-clockwise) of the midgut take place

A

In the umbilical cord around the axis formed by the SMA

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9
Q

When does the second rotation (180 degrees anti-clockwise) of the midgut take place

A

On its return to the abdominal cavity (week 10)

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10
Q

What returns to the abdominal cavity first and last

A

First - cranial limb

Last - cecal bud

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11
Q

During rotation what occurs to the small and large intestine

A

Both elongate

Jejunum and ileum also form a number of coiled loops

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12
Q

Where does the cranial limb move to

A

Left hand side

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13
Q

Where does the cecal bud move to

A

Descends, moving the caecum to the right lower quadrant

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14
Q

Types of malrotation of the midgut

What do both lead to

A

Incomplete rotation
Reversed rotation

Both lead to hypermobility of the gut

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15
Q

Describe incomplete rotation

A

Midgut only rotates 90 degrees anti-clockwise

Results in a left sided colon (small intestine on the right side)

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16
Q

Describe reversed rotation

A

Midgut rotates 90 degrees clockwise

Transverse colon passes posterior to the duodenum so it can be occluded

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17
Q

What is volvulus

A

A bowel obstruction where a loop of the bowel has abnormally twisted in on itself
It can lead to strangulation and ischaemia

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18
Q

Who is more at risk of volvulus

A

People with hyper mobile guts

i.e. Sufferers of malrotation

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19
Q

What’s the end of the hindgut called

A

Cloaca

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20
Q

How is the cloaca separate from the outside

A

Cloacal membrane (single layer of endoderm and ectoderm at the proctodeum)

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21
Q

Describe cloacal partitioning

A

Anteroposterior division of the cloaca
A wedge of mesoderm called the urorectal septum grows down into the cloaca resulting in:
- urogenital sinus anteriorly
- anorectal canal posteriorly
- perineal body where the urorectal septum fuses with the cloacal membrane (outer surface)

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22
Q

Origins of the anal canal

A

Superior part is derived from the hindgut

Inferior part is derived from endoderm

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23
Q

What divides the 2 parts of the anal canal

A

Pectinate line

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24
Q

Anal canal blood supply above the pectinate line

A

Inferior mesenteric artery

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25
Q

Anal canal blood supply below the pectinate line

A

Pudendal artery

26
Q

Anal canal innervation above the pectinate line

A

Parasympathetic - pelvic nerve (S2-4)

27
Q

Innervation blood supply below the pectinate line

A

Pudendal nerve (S2-4)

28
Q

Epithelia type in the anal canal above the pectinate line

A

Columnar

29
Q

Epithelia type in the anal canal below the pectinate line

A

Non keratinised stratified squamous

30
Q

Lymphatic drainage of the anal canal above the pectinate line

A

Internal iliac nodes

31
Q

Lymphatic drainage of the anal canal below the pectinate line

A

Superficial inguinal nodes

32
Q

What sensations are possible above the pectinate line

A

Only stretch

33
Q

What sensations are possible below the pectinate line

A

Temperature
Touch
Pain

34
Q

What is Meckel’s diverticulum

A

A ‘cul-de-sac’ in the ileum

35
Q

What complication is seen in Meckel’s diverticulum

A

Ulceration

Ectopic gastric/pancreatic tissue in the diverticulum secretes enzymes and acids

36
Q

Why is Meckel’s diverticulum said to follow a rule of 2’s

A
2% population affected
2 feet from the iliocecal valve 
2 inches long 
Affects males twice as often as females 
Usually detected in under 2's
37
Q

What is a vitelline cyst

A

Vitelline duct that forms fibrous strands at either end

38
Q

What is vitelline fistula

A

Direct communication between the umbilicus and intestine

39
Q

What is patent urachus

A

The urachus (fibrous remnant of allantois) fails to close so there is a direct communication between the umbilicus and the bladder

40
Q

What is omphalocoele

A

Persistence of a physiological herniation so part of the gut fails to return to the abdominal cavity
Since the umbilical cord is covered by a reflection of the amnion, an epithelial layer covers the defect

41
Q

What is gastroschisis

A

Failure of the abdominal wall to close during embryonic folding leaving the gut tube outside the body cavity
Unlike omphalocoele, there is no covering over the gut tube

42
Q

What are the hindgut abnormalities

A

Imperforate anus
Anal agenesis
Hindgut fistulae

43
Q

What is imperforate anus

A

Failure of the anal membrane to rupture

Also called anal atresia

44
Q

What is anal agenesis

A

Failure of development of the anal canal

45
Q

What is hindgut fistulae

A

Abnormal connection within the hindgut

46
Q

Why is recanalisation necessary in some structures of the gut tube

A

Cell growth becomes so rapid that the lumen is partially or completely occluded

47
Q

What occurs in failure of recanalisation

A

Atresia (complete failure)

Stenosis (partial failure)

48
Q

What’s the order of incidence of atresia/stenosis in the gut

A

Duodenum
Jejunum and ileum
Colon

49
Q

What’s the most common cause of atresia in the upper duodenum

A

Recanalisation failure

50
Q

What’s the most common cause of atresia in the lower duodenum

A

Vascular accident - there is a loss of blood supply and part of the gut dies
Caused by malrotation, volvulus and body wall defects

51
Q

What is pyloric stenosis

A

Narrowing of the exit from the stomach causing projectile vomiting

52
Q

Causes of pyloric stenosis

A

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

53
Q

Which structures of the midgut retain mesenteries

A

Jejunum
Ileum
Appendix
Transverse colon

54
Q

Which structures of the midgut have fused mesenteries

A

Duodenum

Ascending colon

55
Q

Which structures of the hindgut retain mesenteries

A

Transverse colon

Sigmoid colon

56
Q

Which structures of the hindgut have fused mesenteries

A

Descending colon

Rectum

57
Q

When is cloacal partitioning complete

A

End of Week 7

58
Q

When does cloacal partitioning begin

A

Week 6

59
Q

When does a patent urachus present

A

At birth
In men it can present later in life - high pressure caused by obstruction of bladder outflow (by benign prostatic hypertrophy) can lead to opening of urachus

60
Q

How do you distinguish a vitelline fistula and patent urachus

A

Inject contrast into cyst and see whether dye goes into bladder or intestines