02.2 Embryonic Development Flashcards
What is the external lining of the gut derived from?
Splanchinic mesoderm
What is a foregut derivative?
Oesophagus Stomach Pancreas Liver Gallbladder Duodenum (proximal to bile duct entrance)
What a re the derivatives of the midgut?
Duodenum (distal to the bile duct) Jejunum Ileum Caecum Ascending colon Proximal 2/3 of transverse colon
What are the derivatives of the hind gut?
Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of the bladder and urethra
What supplies blood to the foregut?
Coeliac trunk
What supplies blood to the midgut?
Superior mesenteric artery
What supplies blood to the hind gut?
Inferior mesenteric artery
Which organs of the GI tract have a mixed blood supply?
Duodenum
Pancreas
Both have both coeliac trunk and superior mesenteric artery blood supply.
What is a mesentery?
Double layer of peritoneum suspending the gut tube from the abdominal wall
What mesentery is present on the foregut, midgut and hindgut?
Dorsal mesentery
What mesentery is only present on the foregut?
Ventral mesentery
What forms the greater omentum?
Dorsal mesentery
What forms the lesser omentum and what can therefore be conducted?
Ventral mesentery
The free edge can conduct the portal triad
What does stomach rotation create?
Greater and lesser omenta
Repositions stomach so that greater curvature is inferior and left and the cardia and pylorus are away from the midline.
What forms the barrier between the oesophagus and the trachea?
Tracheoesophageal septum
What abnormalities can occur from the tracheoesophageal septum?
Proximal blind end oesophagus
Tracheoesophageal fistula
What forms the liver?
The hepatic bud within the central mesentery
What does the term secondarily retroperitoneal mean?
Began development in the peritoneum but excessive growth causes the mesentery to be lost through fusion at the posterior abdominal wall.
What are the secondarily retroperitoneal structures of the foregut?
Duodenum (except cap)
Pancreas
Why does the midgut run out of space in the abdomen?
Elongates very quickly
Liver is in the way
What is the axis of the midgut loop?
Superior mesenteric artery
Vitelline duct
After physiological herniation into the umbilical cord how does the midgut rotate?
270 degrees anti-clockwise
First turn during herniation
Cranial limb then returns first moving it to the left side
Caecum then descends
What are common types of malrotations of the midgut and what do they result in?
Incomplete rotation - only makes one 90 degree rotation - left sided colon
Reversed rotation - makes one 90 degree rotation but clockwise - transverse colon is posterior to the duodenum
What is a potential complication of midgut rotation defects?
Volvulus
What is the internal lining of the gut formed from?
Endoderm
What is the external lining of the gut derived from?
Splanchinic mesoderm
What is a foregut derivative?
Oesophagus Stomach Pancreas Liver Gallbladder Duodenum (proximal to bile duct entrance)
What a re the derivatives of the midgut?
Duodenum (distal to the bile duct) Jejunum Ileum Caecum Ascending colon Proximal 2/3 of transverse colon
What are the derivatives of the hind gut?
Distal 1/3 transverse colon Descending colon Sigmoid colon Rectum Upper anal canal Internal lining of the bladder and urethra
What supplies blood to the foregut?
Coeliac trunk
What supplies blood to the midgut?
Superior mesenteric artery
What supplies blood to the hind gut?
Inferior mesenteric artery
Which organs of the GI tract have a mixed blood supply?
Duodenum
Pancreas
Both have both coeliac trunk and superior mesenteric artery blood supply.
What is a mesentery?
Double layer of peritoneum suspending the gut tube from the abdominal wall
What mesentery is present on the foregut, midgut and hindgut?
Dorsal mesentery
What mesentery is only present on the foregut?
Ventral mesentery
What forms the greater omentum?
Dorsal mesentery
What forms the lesser omentum and what can therefore be conducted?
Ventral mesentery
The free edge can conduct the portal triad
What does stomach rotation create?
Greater and lesser omenta
Repositions stomach so that greater curvature is inferior and left and the cardia and pylorus are away from the midline.
What forms the barrier between the oesophagus and the trachea?
Tracheoesophageal septum
What abnormalities can occur from the tracheoesophageal septum?
Proximal blind end oesophagus
Tracheoesophageal fistula
What forms the liver?
The hepatic bud within the central mesentery
What does the term secondarily retroperitoneal mean?
Began development in the peritoneum but excessive growth causes the mesentery to be lost through fusion at the posterior abdominal wall.
What are the secondarily retroperitoneal structures of the foregut?
Duodenum (except cap)
Pancreas
Why does the midgut run out of space in the abdomen?
Elongates very quickly
Liver is in the way
What is the axis of the midgut loop?
Superior mesenteric artery
Vitelline duct
After physiological herniation into the umbilical cord how does the midgut rotate?
270 degrees anti-clockwise
First turn during herniation
Cranial limb then returns first moving it to the left side
Caecum then descends
What are common types of malrotations of the midgut and what do they result in?
Incomplete rotation - only makes one 90 degree rotation - left sided colon
Reversed rotation - makes one 90 degree rotation but clockwise - transverse colon is posterior to the duodenum
What is a potential complication of midgut rotation defects?
Volvulus
What is the internal lining of the gut formed from?
Endoderm
What is the difference between a vitelline cyst and a vitelline fistula?
Vitelline cyst is a pocket where the vitilline duct used to be that does not open up onto the umbilicus or the midgut
Vitelline fistula is a fully patent vitelline duct where the midgut can communicate with the umbillicus
Other that a vitelline cyst or fistula what other abnormality can occur due the the remnants of the vitelline duct?
Meckel’s diverticulum
Where is the most likely place for recanalisation to fail?
Duodenum
What can happen if recanalisation of the GI tract is unsuccessful?
Atresia
Stenosis
Why is pyloric stenosis not an example of recanalisation failure?
Actually due to pyloric sphincter hypertrophy
What is gastroschisis?
Failure of closure of the abdominal wall during folding of the embryo. This leaves the gut tube and derivatives outside the body cavity.
What is omphalocoele/exomphalos?
Persistence of physiological herniation
This is different to an umbilical hernia as there is no skin covering
What is the pectinate line?
The line that splits the histologically different upper and lower anal canal
What is the difference between the epithelia above and below the pectinate line?
Above - columnar epithelium
Below - stratified squamous epithelium
What is the difference in blood supply above and below the pectinate line?
Above - IMA
Below - Pudenal artery
What is the difference in nervous supply above and below the pectinate line?
Above - parasympathetic pelvic nerve
Below - pudenal nerve
What are potential hindgut abnormalities?
Imperforate anus
Hindgut fistulae (eg rectum to bladder)
Anorectal agenesis
