Peritoneal and GI Development Flashcards
What does the foregut develop into
- Oesophagus (then into respiratory diverticulum)
- Stomach
- Proximal duodenum
- Liver and biliary system
- Pancreas
- Spleen
Which axis does the stomach rotate around
- Longitudinal
- AP
What does the foregut terminate at
Oropharyngeal membrane
What does the hindgut terminate at
Cloacal membrane
Which part of the gut tube develops faster
Dorsal part
What does the rotation of the stomach mean for the vagal nerves
-Left vagus ends up on anterior surface
Where does the liver develop
- Anterior surface of duodenum
- On right side of body
What does sagittal rotation lead to
Lesser curvature of stomach faces slightly upwards
What does rotation of stomach mean for the duodenum
- Duodenum rotates as well
- Displaces the duodenum to right until it lies against the dorsal body wall and becomes partially retroperitoneal
What happens to pancreas and duodenum
- Reabsorbed by visceral peritoneum
- Secondarily retroperitoneal
Formation of liver
- Hepatic plate appears on ventral side of duodenum
- Hepatic plate grows into hepatic diverticulum
- Hepatic diverticulum grows towards and into the septum transversum
What does the hepatic diverticulum give rise to
- Hepatoblasts (which become hepatocytes and bile canaliculi)
- Septum transverses (develops into liver sinusoids)
How is the bare area of the liver formed
The ventral mesentery reflects onto the diaphragm
How does the liver rotate
Right (with stomach and duodenum)
What is the falciform ligament
- Liver’s communication with anterior wall
- From ventral mesentery
Where does the cystic diverticulum develop
- Ventral side of the duodenum
- Inferior to hepatic diverticulum
What does the cystic diverticulum form
- Gallbladder
- Cystic duct
Where does the pancreas develop
Inferior to hepatic bud
How does the pancreas develop
- 2 buds appear (1 anterior and 1 posterior to duodenum), the ventral and dorsal buds
- The ventral bud gives rise to the uncinate process
- Rotation of the duodenum causes the ventral bud to migrate around to lie behind and fuse with the dorsal bud
Describe the development of the pancreatic ducts
- When the ventral and dorsal pancreatic buds fuse, their ductal systems become interconnected
- Proximal portion of duct of dorsal pancreas degenerates
- The ducts of dorsal and ventral buds unite to form the main pancreatic duct
What is the accessory duct
A remnant of the proximal part of the duct of dorsal pancreas
What does the spleen develop from
Dorsal mesenchyme (in dorsal mesentery- not product of gut tube endoderm)
Where does the spleen end up after rotation
Displaced to the left
What is the portion of dorsal mesentery between spleen and stomach called
Gastrosplenic ligament
What does the midgut form
- Distal duodenum
- Jejunum
- Ileum
- Caecum
- Ascending colon
- Proximal 2/3 of transverse colon
Give an example of a physiological herniation
Presumptive ileum grows faster than other parts of midgut, so grows into umbilical cord (forming the primary intestinal loop)
Which artery grows with the primary intestinal loop
Superior mesenteric
Total degrees of rotation of the midgut
270
Which direction does the primary intestinal loop rotate
Counter-clockwise (as viewed from ventral side)
Where does the ileum and large intestine end up after intestinal rotation
- Ileum= right abdomen
- Large intestine= left abdomen
What closes the hindgut
Cloacal membrane
What is the cloaca
- Dilated space around cloacal membrane
- Has a diverticulum called Allantois
Function of Allantois
Connects the gut tube to yolk sac by entering umbilical cord
What does the hindgut form
- Distal 1/3 of transverse colon
- Descending and sigmoid colon
- Upper 2/3 of anorectal canal
What divides the cloaca
Coronal urorectal septum
What does the urorectal septum divide the cloaca into
- Anteriorly= urogenital sinus
- Posteriorly= anorectal canal
What does the urogenital sinus develop into
Urogenital structures
What does the anorectal canal develop into
Proximal 2/3 of anal canal
How does the cloacal membrane rupture
As the tip of the urorectal septum approaches the cloacal membrane, the anal part of the membrane sinks into the anal pit and the membrane ruptures
What does the urorectal septum do
Joins outside ectoderm and becomes the perineal body
What marks the boundary between hindgut endoderm and ectoderm
Pectinate line
What does the free caudal margin of the falciform ligament carry
Umbilical vein from body wall to liver
How is the lesser omentum formed
By the ventral mesentery between liver and lesser curvature
What does a patent vitelline duct cause
-Faecal discharge at umbilicus
Describe anular pancreas
- If there is a bi-lobed ventral pancreas, can migrate in opposite directions around duodenum
- Can strangulate duodenum
What is Hirschsprung disease
- Lack of normal development of colonic innervation
- Leads to a constricted aganglionic segment of bowel, with a distended segment proximally (the innervation of which is normal)
What is a urorectal/rectovaginal fistula
Where the hindgut does not travel down into skin and opens into urethra/vagina instead
What is a rectoperineal fistula
A narrowing of rectum
What is an imperforated anus
Anal membrane doesn’t rupture and remains closed
What is gastroschisis
Herniation of the small intestine through a defect on either side of the umbilicus
What is exomphalos
Defect on abdominal wall, through which anything can herniate
What is an umbilical hernia
Where the umbilicus cannot close
How to treat an umbilical hernia
Cover with a bandage, usually closes by itself
Give examples of rotational abnormalities of the midgut
- Partial rotation
- Abnormal rotation
What is Merkel’s diverticulum
- Patent vitelline ligament
- May cause symptoms like appendicitus
