Embryology

Question 1

Liver, pancreas, duodenum

Answer 1

Begins in the 4th week. Liver bud grows out from the gut tube, and associated cystic diverticulum and ventral pancreatic bud.

Liver bud grows into the septum transversum, forming the liver cells and bile ducts, whilst the mesoderm of the septum transversum forms the conenctive tissue, Kupffer cells and haematopoetic tissue and the vitteline and umbilical veins form the sinusoids.

The diverticulum connection to the gut tube elongates and narrows to form the bile duct and the cystic diverticulum becomes the GB and CD.

The ventral pancreas swings around posteriorly to fuse with the dorsal pancreas bud and the posterior abdominal wall to become a retroperitoneal organ.

Ventral mesentary is part of the septum transversum that becomes membranous and forms the falciform ligament and lesser omentum

Bare area remains where the liver is in contact with the original septum transversum (bare area). The rest is covered in visceral lateral mesoderm as peritoneum

Duodenum lumen becomes obliterated in the second month of life by proliferating cells , but then is recanalised.

Question 2

Diaphragm + defects

Answer 2

Forms in the 7th week from the fusion of the septum transversum, bilateral pleuroperitoneal membranes, the mesentary of the oesophagus and later from ingrowth of the C3-C5 somite muscles.

Failure of the pleuroperitoneal membranes to fuse leads to CDH
- bochdalek hernia is a posterolateral hernia (85% on right) from failure of pleuroperitoneal membranes to seal.
- Morgagni hernia anteriorly due to failure of the costal and sternal muscles to seal.

Question 3

Branchial arch/pouch/cleft

Answer 3

Arches (mesoderm)
1 - V3 mandibular nerve
2 - Facial nerve
3 - CN IX glossopharyngeal
4 - Vagus
6 - Vagus

Pouch (endoderm)
2- tonsils
3 - inferior parathyroids
4 - superior parathyroids
5 - C cells of thyroid

Cleft (ectoderm)
1st cleft cyst
2nd cleft cyst - most common
3rd cleft cyst