GI Embryology Flashcards
When does the primordial gut tube form and from what?
Week 4 after lateral folding of the embryo from the endoderm lining of the yolk sac
What closes each end of the primordial gut?
An epithelial membrane derived from the ectoderm.
Cranial end = Oropharyngeal membrane
Caudal end = Cloacal membrane
From where are the oropharyngeal and cloacal membranes derived?
Both from depressions in the ectoderm known respectively as the stomodeum and proctodeum (anal pit)
What overall does the endoderm of the primordial gut form?
Most of the gut, epithelium and glands.
From where is the gut muscle derived?
The splanchnic lateral plate mesoderm
What are the derivatives of the foregut?
- Primordial Pharynx (& derivatives)
- Lower Resp. Tract
- Oesophagus & Stomach
Duodenum (Section above the bile & pancreatic duct) - Liver, Biliary apparatus & pancreas
Name 3 pathologies related to development of the lower resp tract and oesophagus:
- Oesophageal Atresia
- Tracheo-Oesophageal -
Fistula - Polyhydramnios
Define Oesophageal Atresia?
Failure of the oesophagus to recanalize, essentially becoming blocked
Define Tracheo-oesophageal fistula>
The septum deviates abnormally causing a connection between the two tubes
Define Polyhydramnios?
Oesophageal Atresia leads to fluid collecting in the amniotic sac due to a lack of swallowing
How does the stomach move after creation and what does this cause?
The stomach rotates 90 degress clockwise
- Forms the lesser sac (or omental bursa)
- Causes the left vagus nerve to supply its anterior surface and the right its posterior surface
What is hypertrophic pyloric stenosis?
Hypertrophy of smooth muscle in the pylorus of the stomach causes stenosis, so no fluids can exit the stomach to the duodenum.
- The child cant eat and will vomit everything up,
- Most common in men.
- Treated surgically
What forms the liver and biliary apparatus?
The hepatic diverticulum from the foregut
Name one developmental pathology of the liver and one of the bile duct?
Accessory Hepatic Ducts
Extrahepatic Biliary Atresia (Obliterated bile ducts)
How does the pancreas form?
Dorsal and Ventral pancreatic bud form from the foregut and fuse when the stomach rotates
Name 2 developmental pathologies of the pancreas?
Annular pancreas
- A failure of the ventral bud to migrate around the duodenum properly
- May cause duodenal stenosis
Accessory Pancreatic tissue
- Forms in other areas of foregut
How does the spleen form?
End of week 4 & week 5, it develops from mesenchyme
What are the derivitives of the midgut?
- Distal Duodenum
- Jejunum
- Ileum
- Caecum
- Appendix
- Ascending Colon
- proximal 2/3rds of transverse colon
How does the midgut loop develop?
1) Physiological umbilical herniation - It herniates into the umbilical cord for more space
2) Rotation of midgut loop - rotates 90 degrees counterclockwise within the umbilical cord
3) Retraction of Intestinal loops - Pulls out of umbilical cord and goes 180 degrees further counter clockwise
4) Fixation of intestines - Intestines become fixed to the abdominal wall, particularly duodenum
Name 5 developmental pathologies of the midgut?
- Meckels Diverticulum
- Omphalocele
- Gastroschisis
- Abnormal Rotation
- Reversed Rotation
Explain Meckels Diverticulum:
A small vitelline duct persists attaching midgut to umbilicus Can develop into a: - Cyst - Fistula - Ligament
Explain Omphalocele?
Herniated loops fail to retract and abdominal viscera remains herniated through an enlarged umbilical ring
Viscera are still covered in a later of amnion
Explain Gastroschisis::
Abdominal contents herniate directly through a the abdominal wall into the amniotic cavity.
They are uncovered by peritoneum or amnion
Occurs through a weak area right of the umbilicus
What is included in the hindgut?
- Distal 1/3rd of the transverse colon
- Descending Colon
- Sigmoid Colon
- Rectum
- Anal Canal
Also forms the lining of the bladder and urethra
