Lecture 4 - Development of the Gut

Question 1

What occurs in the process of gastrulation?

Answer 1

Early developmental process where the ball of cells (blastula) reorganises into a multi-layered organism (tri-laminar disc), consisting of the ectoderm, mesoderm, and endoderm.

Question 2

What does the paraxial mesoderm, intermediate mesoderm and lateral plate of the mesoderm (of the trilaminar disc) go onto form?

Answer 2

Paraxial mesoderm = develop into somites which form skeletal muscle, vertebra and cartilage.

Intermediate mesoderm = forms the kidneys and gonads

Lateral plate of mesoderm = has two divisions which are somatic mesoderm and splanchnic (visceral) mesoderm

Question 3

What is the result of cranio-caudal folding for the GI tract

Answer 3

• Cranio-caudal folding allows tri-laminar disc to develop into something that resembles GIT
• Causes the opening of the gut tube to the yolk sac to draw shut (like a purse string)
• This forms pockets which will become our future foregut, midgut and hindgut. Midgut stays open to hindgut. FORMED FROM ENDODERM LINING.

Question 4

What other kind of folding occurs alongside craniocaudal folding?
What is the result of this folding?

Answer 4

• Lateral folding (transverse)
• Endodermal layer becomes gut tube, mesodermal layer fuses together to form complete ventral abdominal wall
• Somatic portion of lateral wall forms body walls/somatopleuric mesoderm, Splanchnic portions form splanchnopleuric mesoderm

Question 5

What are the bucopharyngeal and cloacal membranes?

When do these rupture?

Answer 5

• Bucopharyngeal and cloacal membranes are sites for the future oral and anal openings.
• 4th and 7th week respectively

Question 6

What 3 anterior branches of the aorta go onto supply the foregut, midgut and hindgut?

Answer 6

Foregut = Coeliac Artery 
Midgut = Superior Mesenteric Artery
Hindgut = Inferior Mesenteric Artery

Question 7

Which structures are included in the foregut, midgut and hindgut?

Answer 7

Foregut = oesophagus –> 2nd part of duodenum where bile duct comes in (+ respiratory tract)

Midgut = 2nd part of duodenum –> 2/3 along transverse colon

Hindgut = 2/3 along transverse colon –> anal canal (+ cloaca)

Question 8

What develops in the foregut to allow for the trachea and oesophagus to be established?

Answer 8

Transoesophageal septum

Question 9

What mesenteries does the foregut, midgut and hindgut have?

Answer 9

• Foregut has ventral and dorsal mesenteries, mid and hindgut only have dorsal, leaving a free edge underneath foregut ventral mesentery

Question 10

What is the parietal and visceral peritoneum derived from?

Answer 10

parietal = somatic mesoderm (so pain arising from here is well localised)
visceral = splanchnic mesoderm (so pain arising from here if vague)

Question 11

Why does foregut rotation occur?

Answer 11

• Foregut rotates to allow liver to end up on right and spleen on left, also to produce the lesser sac.
• The peritoneal cavity (potential space between visceral & parietal peritoneum) is formed from the greater and lesser sac