Development Of GI and lungs Flashcards
How is the primitive gut tube formed?
Amnion folds around embryo (cranial to caudal, and laterally) pinching part of the yolk sac (formed by endoderm) to form the primitive gut tube
What is the connection between the yolk sac and the primitive gut tube called?
Vitelline duct
How is the body cavity formed?
The anterior edges of the amnion fuse to cover the embryo on all sides
What is the intraembryonic coelomic cavity?
Cavity surrounding the primitive gut tube formed by the somatopleuric mesoderm (body wall) and splanchnopleuric mesoderm (around gut tube)
What suspends the primitive gut tube from the dorsal body wall?
The dorsal mesentery
What structure separates the peritoneal and pleural cavities?
Septum transversum
Where are cells of the septum transversum found before they separate the two body cavities?
Cranial to the cardiogenic area - cranial/caudal folding brings it to its more caudal positioning
What do hox genes do? How do they influence gut formation? Where do they come from?
Pattern the embryo
Different Hox gene expression determines the type of gut formed
Cells of the splanchnopleuric mesoderm
From what do the trachea and lungs form?
A midline lung bud from the endodermal foregut, caudal to the pharyngeal arches
Which transcription factor initiates lung bud formation?
What is the main factor for outgrowth? Name for type of growth in lung buds?
Initiates = Nkx2.1 Outgrowth = FGF10 - branching morphogenesis
What is an esophagotracheal fistula?
Where the upper esophagus is a blind ending duct and the distal esophagus is connected to the trachea
What other mesentery (not dorsal mesentery) is present to anchor the primitive gut? What two structures does it form and where?
Ventral mesentery
— between liver and stomach = lesser omentum
— between liver and anterior body wall = falciform ligament
When and how does the stomach form?
week 4
Differential growth causes 2 rotations:
1 — left side moves anteriorly (forming greater and left curvatures)
2 — pylorus moves to the right
What induces liver formation? What forms and when?
FGF signalling from cardiac mesoderm induces growth of hepatic diverticulum during week 4
When does first rotation of the midgut occur? Around which axis and by how much in which direction?
Week 6 -around the superior mesenteric artery from the vitelline duct by 90 degrees anti-clockwise
What causes the second rotation of midgut and by how much? During which weeks does this take place?
Retraction of the herniated midgut back into the abdominal cavity which is now large enough for it to fit - by 180 degrees anticlockwise
10th-12th week
What microstructures cause the rotation?
Nodal cilia that create asymmetric gene transcription patterns
What is the common opening of the gut and the urogenital system called?
What partitions them?
Cloaca
Urorectal septum separates
Which cells are the cells of the enteric nervous system derived from?
Neural crest cells
What direction do the enteric nerves migrate?
Cranial to caudal
Hirschsprung’s Disease? Cause?
Failure of neural crest migration so absence of enteric nervous system
Largely affects distal colon, removing its ability to remove stool
Mutations in ligand (GDNF) or receptor (c-ret) that promote survival and proliferation of the enteric nervous system
What is the primary intestinal loop formed by?
Ileum grows quicker than abdominal cavity can accommodate so it loops and herniates into the vitelline duct
