Session 3, Anatomy, & Development of mid/foregut

Question 1

Which structures does the midgut give rise to?

Answer 1

Small intestine, (most of duodenum)
Caecum + Appendix
Ascending colon
Proximal 2/3 transverse colon.

Question 2

What is the primary intestinal loop? How does it form?

Answer 2

Loop that forms as midgut elongates, running out of space.
The loop has:
-Superior mesenteric artery as its axis
-Is connected to the yolk sac by the vitelline duct
-Has cranial, & caudal limbs

Question 3

When does the growth of the primary intestinal loop happen the fastest?

Answer 3

During the 6th week

Question 4

What happens to the intestines during development?

Answer 4

Liver and intestines growing too fast, not enough room in abdominal cavity.
The intestines herniate out of the abdominal cavity into umbilical cord.

Question 5

Describe the movements of the intestinal loop during herniation and re-entry into the abdominal cavity?

Answer 5

3 x 90° turns!
- Turn 90° horizontal as they leave the cavity.
-Turn 90° again as they move back in
- And 90° when back in the abdomen, leaving them ‘horizontal’
(look at diagram)

Question 6

What do the rotations of the intestines in development achieve? Why is it important?

Answer 6

• Forms the loops of small intestine
• Forms the transverse colon (around the SI)
• Forms the caecal bud (caecum + appendix)

Question 7

What are some abnormalities caused by misfolding of the midgut?

Answer 7

• Only one rotation made = Left sided colon.

- Reversed rotation (only one rotation clockwise) = Transverse colon passes POSTERIOR to duodenum.

Question 8

When do must midgut defects present? How do they present?

Answer 8

Ususally in neonatal period.

Strangulation / Ischaemia

Question 9

What is the vitelline duct?

Answer 9

The long narrow tube that joins the yolk sac to the midgut lumen of the developing fetus.

Question 10

What is a Meckel’s diverticulum?

Answer 10

A defect where the vitelline duct persists causing a diverticulum in the intestine of the midgut.

Question 11

Which other defects can arise when a vitelline duct persists?

Answer 11

A Vitelline cyst - forms fibrous strands.

A Vitelline fistula - direct communication between umbilicus and intestinal tract.

Question 12

What is the rule of 2’s for Meckel’s diverticulum?

Answer 12

2% of population
2 feet from ileocaecal valve
Usually detected in under 2’s
2:1 ratio male: female

Question 13

When is recanalisation suitable? Why?

Answer 13

If the cell growth of a structure becomes too rapid, obliterating the lumen (e.g. oesophagus)
Must be operatively reopened, or stenosis/atresia can occur.

Question 14

Where do most atresia / stenosis events occur in development?

Answer 14

In the duodenum.

Question 15

What could be a common cause of projectile vomiting in infants?

Answer 15

Pyloric Stenosis
Hypertrophy of circular muscle around pyloric sphincter.
Causes vomiting as contents of stomach can’t empty as quickly.

Question 16

What is gastroschisis?

Answer 16

Failure of closure of the abdominal wall during folding of embryo.
Gut tube + derivatives outside body cavity.

Question 17

What is an omphalocoele?

Answer 17

Persistence of physiological herniation.

not hernia, as hernia has covering of skin

Question 18

What is an umbilical hernia?

Answer 18

When part of the internals/gut pokes through a weakness in the abdominal wall at the umbilicus (common in infant)
Usually repairs itself within a year after birth.

Question 19

Which structures does the hindgut give rise to?

Answer 19

• Distal 1/3 transverse colon
• Descending colon
• Rectum
• Superior part of anal canal
• Epithelium of urinary bladder

Question 20

What is the pectinate line in the anus?

Answer 20

Line which divides anal canal into histologically distinct superior and inferior parts.
(differences in arterial supply, venous & lymphatic drainage, and innervation)

Question 21

What is the proctodeum?

Answer 21

The junction between two embryonic germ layer, the back ectodermal part of the alimentary canal.
It it will form the lower part of the anal canal.

Question 22

Describe the cells, innervation and blood supply above the pectinate line.

Answer 22

• Inferior mesenteric artery
• S2, 3 + 4 pelvic parasympathetics
• Columnar epithelium
• Lymph. drainage = internal iliac nodes

Question 23

Describe the cells, innervation and blood supply below the pectinate line.

Answer 23

• Pudendal artery
• S2, 3 + 4 pudendal nerve
• Stratified epithelium
• Lymph. drainage = superficial inguinal nodes.

Question 24

What is the difference in sensation in the anal canal above and below the pectinate line?

Answer 24

• Above:
  Only sensation is stretch
• Below:
  Temperature, touch and pain sensitive

Question 25

Where will the visceral pain from the different gut derivatives be felt?

Answer 25

Visceral pain - poorly localised

• Foregut (+ derivatives) = epigastric
• Midgut = periumbilical
• Hindgut = suprapubic

Question 26

What are some common hindgut abnormalities?

Answer 26

• Imperforate anus = failure of anal membrane to rupture.
• Anal/ anorectal agenesis
• Hindgut fistulae (e.g. to bladder)

Question 27

Which midgut/ hindgut structures lose/ have fused mesenteries?

Answer 27

• Duodenum
• Ascending colon
• Descending colon
• Rectum