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Flashcards in Embryology 2 Deck (60)
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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