Embryology

Question 1

Where does the foregut end and start?

Answer 1

Distal oesophagus to halfway along duodenum

Question 2

Where does the midgut end and start?

Answer 2

Halfway along duodenum to the 2/3 along way of transverse colon

Question 3

Where does the hindgut start and end?

Answer 3

Distal 1/3 of transverse colon to the upper anal canal

Question 4

What supplies the foregut?

Answer 4

Coeliac trunk

Symp = greater splanchnic nerve (T5/6-T9)
Para = vagus

Visceral pain felt in epigastric region

Question 5

What supplies the midgut?

Answer 5

Superior mesenteric artery

Symp = lesser splanchnic nerve (T10-11)
Para = vagus

Visceral pain is felt in umbilical region

Question 6

What supplies the hindgut?

Answer 6

Inferior mesenteric artery

Symp = Least splanchnic nerve (T12-L1) and lumbar splanchnic nerves
Para = pelvic splanchnic nerves

Visceral pain is felt in suprapubic region

Question 7

Stages of midgut development

Answer 7

Elongation

Physiological herniation (protusion of abdomen into umbilical cord) - week 6

Rotation (around axis of SMA)

Retraction (back into abdomen) - week 10

Fixation

Question 8

Elongation

Answer 8

Elongation of yolk sac forms primary intestinal loop.

The upper part of loop (cephalic limb) goes on to make the distal part of the duodenum, the jejunum and part of the ileum)

The lower part of the loop (caudal limb) goes on to make the distal part of the ileum, caecum, appendix, ascending colon and proximal 2/3 of transverse colon

Question 9

Physiological herniation

Answer 9

intestinal loops herniate (moves) into umbilical cord in 6th week.

This is because abdominal cavity is too small for the gut loops and liver.

Gut loop starts to rotate 90 degrees anticlockwise around the SMA

Question 10

Rotation

Answer 10

Anticlockwise, First 90 degrees occurs as gut loop herniates. brings caudal limb more cranially.

Question 11

Continued elongation

Answer 11

small intestine develops coils, large intestine also elongates but doesn’t coil

Question 12

Retraction

Answer 12

Week 10, gut loop returns to abdomen. rotates further 180 degrees anticlockwise. Total roation = 270 degrees anticlockwise.

Question 13

Retraction causes position of gut

Answer 13

Jejunum returns first to left side. Then ileum settles towards the right.

Caecum returns last to upper right quadrant.

This video shows it well: https://www.youtube.com/watch?v=AscKR_cQExY

Question 14

Fixation

Answer 14

Some mesenteries come into close contact with posterior abdominal wall and fuse to posterior wall
Considered ‘retroperitoneal’

Fascial layer - Toldt fascia develops between the parietal peritoneum on posterior body wall and the visceral peritoneum on the organ.

Question 15

Which components are fixed?

Answer 15

Duodenum, ascending colon, descending colon and rectum

Question 16

Caecal bud and appendix

Answer 16

McBurneys point. Appendix can be in different positions. If tip is inflamed and makes contact with parietal peritoneum could be atypical presentation if appendix is ticked in unusual place.

Initially dull central pain in umbilical region. Visceral sensory nerves along sympathetic nerves to T10 region of spinal cord, perceived as same as wall.
When irritates parietal peritoneum then pain becomes well localised to overlying skin of anterior abdominal wall. Somatic nerves now involved.

Question 17

Clockwise rotation would result in…

Answer 17

The duodenum lying anteriorly to the colon. Should be posterior.

Question 18

Meckel’s diverticulum

Answer 18

Vitelline duct normally degenerates. But can persist causing out-pouching from the ilium - a ‘diverticulum’. It can ulcerate and bleed, inflammation can mimic appendicitis.

Question 19

Omphalocoele

Answer 19

Midgut loops doesn’t return into the abdomen in the 10th week but remains in umbilical cord. Gut covered in layer of amnion. High mortality as often have other congenital malformations and chromosomal anomalies.