GI Flashcards
How does the gut tube form?
The embryo folds laterally and caudiocranially, pinching off the yolk sac and creating an inner tube running though it.
What structures are derived from the foregut?
Oesphagus to duodenum (proximal to amulla of vata) in liver, gall bladder, spleen and panceas
What structures derive the mid gut?
Duodenum (at amulla of vata) to proximal 2/3 of transverisng colon
What structures derive from the hind gut?
Distal 1/3 transversing colon to upper anal canal, plus bladder and urethra.
What branches of the aerota supply the fore, mid and hind gut structures
The celiac trunk branches supply the forgut
The superior mesenteric structures supply the mid gut and inferior mesenteric structures supply the hindgut.
From where and how do the peritoneal and pleural cavities develop?
They develop from the cavity surrounding the primative gut tube (intraembryonic celom). Splanchnic mesoderm covers the gut tube (becomes visceral layer) and somatic mesoderm covers cavity wall (becomes patietal pleura).
The diaphragm grows and splits it in half- creating the peritoneal and pleural cavities into which structures grow.
Describe the development of the lungs.
The lung bud appears in 4th week as a diverticulum which grows off the ventral (anterior) wall of the foregut. A treacheosphageal septum develops to seperate the forgut and lung buds into seperate tubes.
What develops in the ventral mesentary?
Liver and billary system
What develops within the dorsal mesentary at the foregut level?
The spleen and pancreas
Which way does the stomach rotate?
clock wise, about 90 degrees. This puts the liver on the right, creates the stomach curvatures, puts spleen on the left and bends the duodenum.
List 3 secondarily retroperitoneal structures
- Duodenum
- Pancreas
- Asceding and descending colon
Why are the duodenum and pancreas SECONDARILY retroperitoneal? What happens to their mesentaries?
Because the started off developing within the peritoneum but the rotation of the stomach forced them backwards to become retroperitoneal.
Their mesentaries fuse to make fusion fascias.
What connects the liver to the stomach and to the abdominal wall
To stomach–> the lesser omentum
To abdo wall–> falciform ligament
What connects the spleen to the abdo wall and the stomach?
To abdo wall–> splenorenal ligament
To stomach–> Gastro- splenic ligament
What is physiological herniation of the midgut?
The midgut initially is connected to the yolk sac at the midpoint. The midgut then grows faster than the abdominal cavity to it herniates into the umbilical cord.
Describe the movement of the midgut tube as it herniates.
It rotates 3 times counterclockwise 90 degrees. This puts the distal part (colon) above the proximal part (small intestine), and so everything is in the correct orientation. The cecal bud (primative caecum) then grows downwards (as it is now in the top right), to put the caecum in the bottom right and create an ascending colon.
Describe the formation of the anus
The anal canal descends down to the cloacal membrane, which rises up slightly to form a pit- the proctodeum. This will rupture at some point to form the anus.
Why does the distal anus (below the pectinate line) have a differnt epithelium, blood supply and nervous innervation than above the pectinate line?
Because below the pectinate line is formed from invagination of the ectoderm at the cloacal membrane. Whereas above it is formed from the hindgut.
What is the difference in epithelium, blood supply and nervous supply above and below the pectinate line?
Epithelium goes from columnar to stratified squamous.
Blood supply goes from inferior mesenteric artery to pedendal artery.
Nervous supply goes from S2,3,4 pelvic parasympathetics (stretch sensation only) to S2,3,4 pedendal nerve (pressure, pain, stretch)
What is the differenace between an umbellical hernia and an omphalocele?
Umbellical hernia= large opening between abdo cavity and umbellical cord persisting so intestine can pop out. It has COVERING OF SKIN AND PERTIONEUM.
An omphalocele is persistance of physiological herniation, meaning there is just a thin membranous covering over the top of it.
What happens to the vitelline duct? (connects midgut to umbellical cord)
It regresses and forms the vitelline ligament
What are merckles diverticulums?
Failure of regression of the proximal portion of the vitelline ducts, leaving a small enclosed pouch of intestine, which is susceptible to infections ect.
What is the differance between a vitelline fisula and a vitelline cyst?
Fistula= complete persistance of vitelline duct, GI contents will leak out umbellicus Cyst= proximal and distal parts regress, fluid collects in duct left in middle
What is pyloric stenosis?
Hypertrophy of circular muscle in the region of the pyloric sphincter. It is a cause of projectile vomiting in infants.
What is anal/ anorectal agenesis?
A failure of the hindgut to descend far enough. This is slightly different from imperforate anus where the cloacal membrane doesn’t rupture.
What is an anal fistula?
Connection between anus and bladder of ureter
What is gastrischsis?
Failure of closure of the abdominal wall during folding of the embryo. This leaves the gut tubes on the outside of the body. It has no membranous covering like an omphalocele does though.
Recanalisation defects may lead to atresia (complete lack of lumen) or stenosis (partial failure), where are they most common?
The duodenum.
