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Flashcards in Embryology 2 Deck (60):
1

What is the primary intestinal loop

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

2

Features of the primary intestinal loop

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)

3

Adult derivatives of cranial limb

Distal duodenum
Jejunum
Proximal ileum

4

Adult derivatives of caudal limb

Distal ileum
Caecum
Appendix
Ascending colon
Proximal 2/3 transverse colon

5

What is physiological herniation

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

6

When does physiological herniation occur

Week 6

7

How much does the midgut rotate overall

270 degrees anticlockwise

8

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

In the umbilical cord around the axis formed by the SMA

9

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

On its return to the abdominal cavity (week 10)

10

What returns to the abdominal cavity first and last

First - cranial limb
Last - cecal bud

11

During rotation what occurs to the small and large intestine

Both elongate
Jejunum and ileum also form a number of coiled loops

12

Where does the cranial limb move to

Left hand side

13

Where does the cecal bud move to

Descends, moving the caecum to the right lower quadrant

14

Types of malrotation of the midgut
What do both lead to

Incomplete rotation
Reversed rotation

Both lead to hypermobility of the gut

15

Describe incomplete rotation

Midgut only rotates 90 degrees anti-clockwise
Results in a left sided colon (small intestine on the right side)

16

Describe reversed rotation

Midgut rotates 90 degrees clockwise
Transverse colon passes posterior to the duodenum so it can be occluded

17

What is volvulus

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

18

Who is more at risk of volvulus

People with hyper mobile guts
i.e. Sufferers of malrotation

19

What's the end of the hindgut called

Cloaca

20

How is the cloaca separate from the outside

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

21

Describe cloacal partitioning

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)

22

Origins of the anal canal

Superior part is derived from the hindgut
Inferior part is derived from endoderm

23

What divides the 2 parts of the anal canal

Pectinate line

24

Anal canal blood supply above the pectinate line

Inferior mesenteric artery

25

Anal canal blood supply below the pectinate line

Pudendal artery

26

Anal canal innervation above the pectinate line

Parasympathetic - pelvic nerve (S2-4)

27

Innervation blood supply below the pectinate line

Pudendal nerve (S2-4)

28

Epithelia type in the anal canal above the pectinate line

Columnar

29

Epithelia type in the anal canal below the pectinate line

Non keratinised stratified squamous

30

Lymphatic drainage of the anal canal above the pectinate line

Internal iliac nodes

31

Lymphatic drainage of the anal canal below the pectinate line

Superficial inguinal nodes

32

What sensations are possible above the pectinate line

Only stretch

33

What sensations are possible below the pectinate line

Temperature
Touch
Pain

34

What is Meckel's diverticulum

A 'cul-de-sac' in the ileum

35

What complication is seen in Meckel's diverticulum

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

36

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

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

What is a vitelline cyst

Vitelline duct that forms fibrous strands at either end

38

What is vitelline fistula

Direct communication between the umbilicus and intestine

39

What is patent urachus

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

40

What is omphalocoele

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

What is gastroschisis

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

What are the hindgut abnormalities

Imperforate anus
Anal agenesis
Hindgut fistulae

43

What is imperforate anus

Failure of the anal membrane to rupture
Also called anal atresia

44

What is anal agenesis

Failure of development of the anal canal

45

What is hindgut fistulae

Abnormal connection within the hindgut

46

Why is recanalisation necessary in some structures of the gut tube

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

47

What occurs in failure of recanalisation

Atresia (complete failure)
Stenosis (partial failure)

48

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

Duodenum
Jejunum and ileum
Colon

49

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

Recanalisation failure

50

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

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

51

What is pyloric stenosis

Narrowing of the exit from the stomach causing projectile vomiting

52

Causes of pyloric stenosis

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

53

Which structures of the midgut retain mesenteries

Jejunum
Ileum
Appendix
Transverse colon

54

Which structures of the midgut have fused mesenteries

Duodenum
Ascending colon

55

Which structures of the hindgut retain mesenteries

Transverse colon
Sigmoid colon

56

Which structures of the hindgut have fused mesenteries

Descending colon
Rectum

57

When is cloacal partitioning complete

End of Week 7

58

When does cloacal partitioning begin

Week 6

59

When does a patent urachus present

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

How do you distinguish a vitelline fistula and patent urachus

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