Lecture 5 Development Of The Midgut

Question 1

Primary intestinal loop

Answer 1

The midgut elongates enormously and runs out of space
Therefore makes a loop connected to the yolk sac by the vitelline duct
Has a cranial and caudal limb on a SMA axis

Question 2

Physiological herniation

Answer 2

6th week of development
Growth of the primary intestinal loop is rapid and elongates
The abdominal cavity is too small therefore the intestines herniate into the umbilical cord

Question 3

Midgut rotation

Answer 3

Turns 90 degrees to the right during herniation
Turns 90 degrees after herniation
Turns 90 degrees when returning to the abdominal cavity

Therefore - cranial end is on the left of the superior mesenteric artery

Question 4

Descent of caecal bud

Answer 4

Caecum descends down to the right iliac fossa with the appendix

Question 5

Malrotation

Answer 5

Incomplete rotation

• midgut only makes one 90 degree turn
• left sided colon

Reversed rotation

• midgut makes one 90 degrees rotation clockwise
• transverse colon passes posterior to the duodenum

Question 6

Risks associated with midgut defects

Answer 6

Occurs in neonatal period:
Volvulus
- strangulation
- ischaemia
- duodenal obstruction by large intestine
- compression of transverse colon by SMA
- duodenal dilation due to volvulus of small intestine

Question 7

Vitelline duct defects

Answer 7

The vitelline duct can persist causing:

• vitelline cyst
• vitelline fistula
• Meckel’s diverticulum

Question 8

Vitelline cyst

Answer 8

forms fibrous bands between the small intestine, vitelline duct and umbilicus

Question 9

Vitelline fistula

Answer 9

• direct communication between the umbilicus and intestinal tract

Question 10

Meckel’s diverticulum

Answer 10

Blind ended outpouching of the small intestine with or without fibrous band formation

Especially in the ileum

2% of population
2 ft from the ileocaecal valve
Usually in under 2 yrs old
2x more likely to get it if male

Can contain ectopic pancreatic or gastric tissue

Question 11

Recanalisation

Answer 11

In some gut structures, cell growth becomes so rapid that the lumen is partially or fully occluded

Recanalisation restores the lumen

Question 12

Failure of recanalisation

Answer 12

Atresia or stenosis

Question 13

Where does recanalisation occur?

Answer 13

Oesophagus
Bile duct
Small intestines - duodenum

Question 14

Atresia

Answer 14

No lumen as completely occluded

Question 15

Why causes failure of duodenal recanalisation

Answer 15

Vascular accidents

• lower duodenum
• due to volvulus, malrotation or body wall defect

Incomplete canalisation
- upper duodenum

Question 16

Pyloric stenosis

Answer 16

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

Not due to failure of recanalisation

Common in infants

Question 17

Characteristic symptom of pyloric stenosis

Answer 17

Projectile vomiting

Question 18

Gastroschisis

Answer 18

Failure of closure of the ventral abdominal wall during embryonic folding
Gut tube and derivatives outside body cavity
Visceral not covered by peritoneum therefore exposed to amniotic fluid
Problems with gut development e.g.
- intestinal atresia
- short inflamed gut
- feeding problems

Less genetic complications therefore better survival than omphalocele
High mortality rate

Question 19

Omphalocele

Answer 19

Persistent physiological hernia
Abdominal cavity may not grow enough to accommodate viscera
Covered by peritoneum
Associated with genetic complications therefore worse survival rate but can be closed at birth

Question 20

Structures of the anal canal

Answer 20

Superior anal canal
Pectinate line
Inferior anal canal

Question 21

Proctodeum

Answer 21

Anal pit
Small depression in the caudal most region of the embryo
The proctodeum ruptures and the ectoderm is pushed up

Question 22

Above pectinate line

Answer 22

Supplied by: IMA
Innervation: pelvic parasympathetic nerves S2,3,4
Epithelium cells: columnar
Lymph drainage: internal iliac nodes

Question 23

Below pectinate line

Answer 23

Supplied by: Pudendal artery
Innervation: pudendal nerve S2,3,4
Epithelium cells: stratified squamous
Lymph drainage: superficial inguinal nodes

Question 24

Sensation above pectinate line

Answer 24

Stretching

Question 25

Sensation below the pectinate line

Answer 25

Temperature
Pain
Touch

Question 26

Visceral referred pain

Answer 26

Foregut - epigastrium
Midgut - periumbilical
Hindgut - suprapubic

Question 27

Hindgut abnormalities

Answer 27

Imperforate anus - failure of anal membrane to rupture
Anal agenesis - incomplete development of anorectum
Hindgut fistula - channel between rectum and bladder

Question 28

Cranial limb of midgut

Answer 28

Distal duodenum to proximal ileum

Question 29

Caudal limb of midgut

Answer 29

Distal ileum to proximal 2/3 of transverse colon

Question 30

Gastrolienal ligament

Answer 30

Dorsal mesentery from stomach to spleen

Question 31

Lienorenal ligament

Answer 31

Dorsal mesentery from spleen to kidney

Question 32

Midgut supply, innervation

Answer 32

Supply: superior mesenteric artery and vein

Innervation:

• parasympathetic - vagus nerve
• sympathetic - superior mesenteric ganglion and plexus

Question 33

Hind gut supply and innervation

Answer 33

Supply: inferior mesenteric artery and vein

Innervation:

• parasympathetic - pelvic nerves S2,3,4
• sympathetic - inferior mesenteric ganglion and plexus