12 Peritoneal and GI development 2 Flashcards
What does the ventral mesentery end and what does it form?
- Ends 1/2 way along duodenum
- Therefore:
Falciform ligament and lesser omentum have free edges
What arteries are in dorsal mesentery?
Celiac, superior mesenteric and inferior mesenteric arteries
Where does the foregut extend to and from?
Mouth –> distal to developing liver
What supplies the foregut?
Celiac trunk
Where is the referred pain of foregut?
To epigastrium
What does the foregut give rise to?
- Oesophagus (that gives the respiratory diverticulum that forms the trachea & lungs)
- Stomach
- Proximal duodenum
- Liver & biliary system
- Pancreas
- Spleen
What does abnormal trachea-oesophageal development in foregut give rise to?
Trachea-Oesophageal fistula
What occurs to the oesophagus length in the foregut during development?
Initially short but lengthens with descent of heart
When does the development of stomach appear in the foregut?
- Week 4
* Dilation of foregut
Describe the rotation of stomach during development
It rotates around both at a longitudinal & an anterior-posterior axis:
• 90° clockwise around the longitudinal axis so the left side faces anteriorly & the lesser curvature faces to the right while the greater curvature faces to the left
• Anterior-posterior axis so the pyloric part comes to lie on the right & the oesophago-
gastric junction slightly left so that the greater curvature faces left & inferiorly
Describe the sequence of events during the formation of the duodenum from the foregut
- Formed from foregut and beginning of midgut
- Initially found in midline but rotations of stomach cause duodenum to rate and swing to the right
- “Falls” onto posterior abdominal wall and becomes retroperitoneal (except for proximal 1st part - remains intraperitoneal)
- During development, the lumen of duodenum becomes obliterated by a proliferation of cells and then it’s re-canalised
Describe the sequence of events during the formation of the liver and gallbladder from the foregut
- Liver develops from an endodermal bud during week 3
- Penetrates the ventral mesentery & septum transversum
- Gives rise to the hepatic ducts & gallbladder
- The ventral mesentery directly in contact with the liver becomes its visceral peritoneum
- Bare area of the liver is where it contacts the diaphragm with no intervening peritoneum
Describe the sequence of events during the formation of the pancreas from the foregut
- Pancreas forms from dorsal and ventral endodermal buds from the duodenum
- The rotation of the latter causes the ventral bud to migrate around to lie behind and fuse with the dorsal bud so that the adult pancreas lies in the curve of the duodenum
- The ducts of the dorsal and ventral buds unite to form the main pancreatic duct
- The accessory duct is the remnant of the duct of the dorsal bud
Name the congenital abnormalities in foregut?
- Duplication of parts of biliary system - e.g. gallbladder
2. Annular pancreas
How does an obstructive annular pancreas form?
• The ventral pancreatic buds may consist of 2 lobes that do not fuse & migrate in opposite directions encircling the duodenum
=> Forming an obstructive annular pancreas
What does the rotation of the stomach around its longitudinal axis do to the ventral mesentery?
Throws ventral mesentery (divided into lesser omentum and falciform ligaments by developing liver) to the right
What vein is in the free edge of the falciform ligament?
Umbilical vein
What lies in the free edge of the lesser omentum?
- Common bile duct
- Hepatic artery proper
- Portal vein
What happens when the stomach is rotated around an anterior-posterior axis?
- The fundus goes slightly left, the greater curvature inferiorly & the pylorus to the right & upwards
- The liver is also thrown upwards under the diaphragm
- The free edge of the lesser omentum lies almost vertically between the liver & duodenum
What happens when the stomach is rotated around its longitudinal axis?
- Its posterior aspect (that will become the greater curvature) rotates to the left so that the dorsal mesentery i.e. dorsal mesogastrium (that will become the greater omentum) is thrown to the left as well
- A potential space (lesser sac/omental bursa) is left posterior to the stomach & lesser omentum
Where does the lesser sac (omental bursa) lie? How does it communicate with the greater sac?
- Behind stomach and lesser omentum
* Must communicate with grater sac around the free edge of the lesser omentum (epiploic foramen)
What are the boundaries of the epiploic foramen?
- Anteriorly: free border of the lesser omentum, with the bile duct, the hepatic artery proper, and the portal vein
- Posteriorly: inferior vena cava
- Superiorly: caudate process of the caudate lobe of the liver
- Inferiorly: first part of the duodenum
What is Pringle’s manoeuvre?
- During surgery, when the hepatic artery proper and portal vein are compressed with fingers/ haemostat to control bleeding
- Lesser sac approached via epiploic foramen
How is the greater omentum formed?
- As the dorsal mesentery is thrown left, the stomach rotates on its AP axis and the greater curvature faces inferiorly
- The dorsal mesentery is then dragged with it so that a big, double-layered fold of mesentery, the greater omentum, hangs off the greater curvature
What does the greater omentum hang off of?
- Hangs off the greater curvature
* Lies like an apron in the abdomen in front of transverse colon
Relationship between lesser sac and greater omentum?
- The greater omentum, initially with the lesser sac (omental bursa) extending into it
- The omental layers fuse to obliterate that part of the lesser sac & the greater omentum overlies the transverse colon & small intestine
Boundaries and relations of the lesser sac (omental bursa)
- Anteriorly:
• caudate lobe
of liver
• lesser omentum; stomach - Posteriorly: pancreas
- Laterally:
• left kidney and adrenal gland
• on the right the epiploic
foramen - Superiorly:
• extends as far as the diaphragm - Inferiorly:
• extends a little way between the layers of the greater omentum
How is the spleen formed in the foregut
Forms with the dorsal mesentery of the stomach
What is the lienorenal/ splenorenal ligament?
Dorsal mesentery (double layers of peritoneum) between the spleen and posterior abdominal wall (close to kidney)
What is the gastrolienal/ gastrosplenic ligament?
Dorsal mesentery (double layer) between the spleen and the stomach
What the tail of the pancreas extend into? With which nerves?
Lienorenal/ splenorenal ligament along with splenic nerves
Greater omentum overlies which structures?
Transverse colon and small intestine
Where does the midgut commence and end?
- Immediately distal to entrance of common bile duct into the duodenum
- Ends 2/3 along transverse colon
What is the midgut supplied by?
Superior mesenteric artery
Where is pain from midgut referred to?
Periumbilical region (T10)
What happens at week 5 to the midgut?
- Suspended from the posterior abdominal wall as the primary intestinal loop by a dorsal mesentery
- Connected to yolk sac by vitelline duct
What does the vitelline duct connect?
Connects the primary intestinal loop by a dorsal mesentery (midgut) to the yolk sac
What does rapid growth of intestinal loop in midgut result in?
Physiological herniation through the umbilicus and into the umbilical cord
What does the cranial limb of the loop (midgut) grow to become?
Much of the jejunum and ileum
How does the cranial limb of loop (midgut) rotate?
• The loop rotates in a counter clockwise direction
90° in the physiological hernia
- And then another 180° as the loop drops back into the abdomen at about 70 days (10 weeks)
- Overall this is a total of 270° of rotation around the axis of the SMA
Describe the migration of the caecum during midgut development?
- Initially as the intestine drops back into the abdomen, the jejunum lies to the left & the caecum is up in the right hypochondrium adjacent to the liver
- The caecum with the vermiform appendix then migrate inferiorly to the right iliac fossa
What are the congenital abnormalities that can occur in the midgut?
Vitelline duct:
- Meckel’s diverticulum
- Vitelline cyst
- Vitelline fistula or patent duct
- Gatroschisis
- Exomphalos
- Umbilical hernia
What does failure of recanalisation in midgut development lead to?
Narrowing or even complete obstruction of the gastrointestinal tract at any point
When does cephalic-caudal and lateral folding of trilaminar disc start?
Towards end of week 3 (~ 18 days)
What occur in trilaminar disc folding? What does it create?
• Head and tail folds meet 2 lateral folds at umbilicus
Creates:
• Endodermal tube of pharynx and oesophagus
• Stomach and intestinal tract
• Glands associated with the gastrointestinal tract
What is the hindgut supplied by?
Inferior mesenteric artery
Where is hindgut pain referred to?
Suprapubic region (T12)
What does the hindgut give rise to?
- Distal end of transverse colon (1/3)
- Descending colon
- Sigmoid colon
- Rectum
- Upper 2/3/ anal canal
What does the most inferior part of the hindgut develop into?
Cloaca
What is the cloaca divided by?
Mesodermal urorectal septum
Anterior, what does the cloaca develop into?
Urogenital system
Posteriorly, what does the cloaca develop into?
Anorectal canal
Describe the embryological development of the anal canal?
- The distal aspect of the cloaca is closed by a membrane
- As the surrounding mesoderm & ectoderm proliferate, the anal part of the membrane sinks into the anal pit
- The membrane breaks down at 8 weeks, so that the proximal 2/3 of the anal canal is derived from the hindgut endoderm
- Distal 1/3 is derived from ectoderm
- The pectinate line marks the change in embryological derivation, blood & nerve supply
What are the congenital abnormalities in hindgut?
- Fistuale between anal canal and urogenital organs
2. Imperforate anus
What causes an imperforate anus?
Anal membrane does not break down
What is Hirschsprung disease?
- Lack of normal development of the colonic innervation leads to a constricted aganglionic segment of bowel
- With a distended segment proximally, the innervation of which is normal
