Lecture 6 - Embryology 1

Question 1

where does the primitive gut extend from?

Answer 1

oropharyngeal membrane to cloacal membrane

Question 2

what are the 3 parts of the gut tube and what where do each part extend from?

Answer 2

foregut - mouth to 1st half of duodenum
midgut - 2nd half of duodenum to 2/3rds along transverse colon
Hindgut - distal 1/3rd transverse colon to superior 2/3rd rectum

Question 3

At what point is the midgut continuous with the yolk sac?

Answer 3

vitelline duct

Question 4

What are the components of the primitive gut tube and what is each component derived from?

Answer 4

epithelial lining - endoderm
smooth muscle and connective tissue - visceral mesoderm
visceral and parietal peritoneum - visceral and parietal mesoderm

Question 5

What is the primitive gut tube suspended from the posterior abdominal wall by?

Answer 5

dorsal mesentery

Question 6

What is a mesentery

Answer 6

double fold of peritoneum that encloses an organ and connects to the body wall. these organs are intraperitoneal

Question 7

retroperitoneal

Answer 7

Organs that are not surrounded by peritoneum are called retroperitoneal

Question 8

what does the dorsal mesentery suspend?

Answer 8

from lower oesophagus to cloaca

Question 9

what does the dorsal mesentery suspend?

Answer 9

– from lower oesophagus to 1st part of duodenum

- forms lesser omentum and falciform ligament (umbilical vein)

Question 10

what is the function of the mesentery?

Answer 10

Carry blood supply, lymphatics and nerve supply to and from organs

Question 11

What undergo remodelling to give rise to the arteries of the GIT?

Answer 11

the vitelline arteries

Question 12

Which are the 3 arteries that supply the GIT?

Answer 12

• Coeliac trunk
• Superior Mesenteric - midgut
• Inferior mesenteric - hindgut

Question 13

How does the definitive gut tube lumen form?

Answer 13

week 6

• proliferation of endoderm derived epithelial lining occludes gut tube
• apoptosis occurs for 2 weeks - creates vacuoles - recanalisation
• vacuoles coalesce - fully recanalise by week 9
• epithelium undergoes further differentiation

Question 14

What can abnormal recanalisation cause?

Answer 14

abnormal - duplications of the GI tract

incomplete recanalisation - stenosis or blocked gut tube

Question 15

What are the structures most commonly affected if there is abnormal recanalisation?

Answer 15

ileum followed by duodenum

Question 16

if there is a duplication problem what else can happen

Answer 16

formation of cysts

high incidence of complications - bowel obstruction or intussusception

Question 17

Development of the foregut

Answer 17

Foregut extends from the oropharyngeal membrane to the first part of the duodenum
Gives rise to respiratory diverticulum
Separates from respiratory diverticulum - tracheoesophageal septum – pharynx and oesophagus

Question 18

oesophageal atresia

Answer 18

can happen independently of tracheooesophageal fistula
displacement of septum can separate proximal and distal ends of oesophagus
prevents foetus from swallowing amniotic fluid - returns to mother through placental circulation -

Question 19

What is polyhydramnios

Answer 19

atresia prevents foetus from swallowing amniotic fluid - returns to mother through placental circulation -

surgical repair - 85% survival rate

Question 20

When and how does the oesophagus form?

Answer 20

Forms in week 4 caudal to the lung bud
oesophagus has endodermal epithelial lining and smooth muscle layer from visceral mesoderm.
initially very short

Question 21

What other muscle does the oesophagus have apart from smooth muscle?

Answer 21

skeletal muscle - from paraxial mesoderm

Question 22

congenital hiatal hernia

Answer 22

oesophagus rapidly lengthens in weeks 4-7 to descent to abdomen

• insufficient elongation - results in part of stomach positioned supradiaphragmatically
• differs from common acquired hiatal hernia - irreducible

Question 23

How and when does the stomach form?

Answer 23

The stomach appears in the 4th week as a dilation of the foregut
suspended in abdomen - dorsal and ventral mesenteries
Differential growth in week 5 forms the greater curvature i.e. the dorsal wall grows faster

Question 24

In which direction does the stomach rotate in weeks 7-8?

Answer 24

rotates around 2 axes
90° clockwise rotation around the craniocaudal axis - lesser curvature moves from ventral position to the right.
greater curvature moves from dorsal position to the left

Question 25

What happens to the vagus nerves on the gut tube ?

Answer 25

initially located on left and right sides of gut tube
left vagus trunk - becomes anterior
right vagus trunk - posterior (dorsal)

Question 26

what does the rotation around the ventrodorsal axis do?

Answer 26

greater curvature - faces slightly caudally

lesser curvature - slightly cranially

Question 27

Formation of the Lesser Peritoneal Sac

Answer 27

as stomach rotates - creates space behind it - lesser sac

Question 28

what is the epiploic foramen?

Answer 28

The epiploic foramen (of Winslow) is the narrow opening that connects greater and lesser sacs

Question 29

formation of the greater omentum

Answer 29

dorsal mesentery attached to stomach - greater curvature - continues to grow
reflects back on itself to form lesser sac
both fuse before birth

Question 30

what does the posterior layer of the greater omentum also fuse with

Answer 30

mesentery of the transverse colon

Question 31

Congenital Pyloric Stenosis

Answer 31

Narrowing of pyloric sphincter caused by hypertrophy of smooth muscle
more common in males
1 in 500
restricts gastric emptying

Question 32

signs of pyloric stenosis

Answer 32

Palpable pyloric mass
Projectile vomiting
Visible peristalsis

Question 33

Heterotopic Gastric Tissue

Answer 33

-Inappropriate epithelial differentiation of the gut tube can result in ectopic gastric tissue
-acid production can cause inflammation and ulceration in the surrounding area
Damage can result in strictures due to scarring or rupture of the gut wall

Question 34

What are the 2 origins of the duodenum and how does it form?

Answer 34

proximal half is foregut, distal half is midgut.
The duodenum elongates in week 4 resulting in a ventrally projecting C-shape
This is then dragged to the right by the rotating stomach

Question 35

What happens to the dorsal mesentery attached to the duodenum during development

Answer 35

The dorsal mesentery attached to the duodenum degenerates so that the duodenum lies against the posterior abdominal wall - secondarily retroperitoneal

Question 36

where does the foregut become the midgut

Answer 36

The boundary is distal to the entrance of the common bile duct