development of peritoneum & foregut (part II) - stomach rotation Flashcards
how are the greater & lesser sacs formed? how are the omenta formed?
rotation of the stomach
how does the primitive stomach rotate?
in 2 directions:
around longitudinal axis
around anteroposterior axis
what does the rotation of the stomach result in?
- greater & lesser curvature come to lie first on right & left side (longitudinal)
- then cardia & pylorus move horizontally, pushing greater curvature inferiorly (anteroposterior rotate)
what does anterior and posterior in embryo equal in adults?
superior & inferior
what is the stomach fixed by? what does this means when the stomach rotates?
fixed by anterior & posterior abdominal wall (cranial & caudal), therefore anything around stomach will have to change as a result of the stomach rotating (knock on effects on structures nearby & pull anything attached to greater curvature with it)
describe what happens to dorsal mesentery during rotation around longitudinal axis
dorsal mesentery containing the greater curvature rotates longitudinally from dorsal to left hand side
describe what happens to ventral mesentery during rotation around longitudinal axis
ventral mesentery rotates longitudinally to anatomical right side (lesser curvature & omentum)
what is the stomach attached to?
attached to anterior and posterior abdominal wall - because in the foregut
what allows for the rotation of the stomach to occur?
pliable membrane - able to move and create complex fold in membranes
describe what happens in rotation around anteroposterior axis?
- dilation of foregut - where stomach will develop
- stomach rotating - pushing down (inferior) almost to horizontal
- (greater & lesser curvature produced)
what happens to the dorsal mesentery in rotation around the longitudinal axis?
a bulge is created in the dorsal mesentery from membrane twisting to follow stomach wall - becomes greater curvature
what happens to the dorsal mesentery in rotation around anteroposterior axis?
gives rise to the omental bursa (greater omentum) suspended from greater curvature of stomach (as that is where the dorsal mesentery was attached to the stomach)
what is significant about greater & lesser sac?
continuous with each other & can communicate with each other
clinically: fluid in one can travel to the other
what does rotation of the stomach result in?
- puts vagus nerves anterior & posterior to the stomach instead of L & R
- shifts cardia (superior) & pylorus (inferior) from midline (stomach lies obliquely - anteroposterior rotation)
- contributes to moving lesser sac behind stomach
- creates greater omentum
what is a peritoneal reflection?
a change in direction:
1. from parietal peritoneum to mesentery
2. from mesentery to visceral peritoneum
etc.
what are structures without mesentery called? why?
retroperitoneal - as they are not suspended within the abdominal cavity
what are retroperitoneal structures specifically?
were never in the peritoneal cavity & never had a mesentery (EVER)
what are secondarily retroperitoneal structures?
began development invested by peritoneum, had a mesentery, BUT with successive growth & development, the mesentery is lost through fusion at posterior abdominal wall
where does the foregut extend from to?
from the lung bud to the liver bud
what happens in the 4th week to the ventral wall of the foregut?
a respiratory diverticulum forms in the ventral wall of the foregut at the junction with the pharyngeal gut
what does the respiratory diverticulum create?
- respiratory primordium (ventrally - respiratory tract)
2. oesophagus (dorsally)
what happens after the respiratory diverticulum has developed?
the respiratory diverticulum bulges out of the ventral wall of foregut, tracheoesophageal septum then develops to close off the division of ventral and dorsal, creating separate tubes for oesophagus and respiratory tract
what are some of the consequences of abnormal positioning of the tracheoesophageal septum?
- proximal blind - end oesophagus (immediately symptomatic in babies - they aspirate, difficulty feeding)
- tracheoesophageal fistula (abnormal passageway between trachea & oesophagus)
what happens to the stomach once it has rotated into the correct position?
growth:
- slight dilation of distal foregut indicates position of stomach primordium (embryonic stomach)
- faster growth of dorsal border - creates greater curvature
what happens after faster growth of greater curvature?
stomach rotates, changing position of the dorsal & ventral mesentries
what does ‘stomach rotates, changing position of the dorsal & ventral mesentries’ achieve?
- omental bursa formed
2. lesser sac displaced posteriorly from right (right to back - lesser, left to front - greater)
what are foregut-derived glands formed in the ventral mesentery?
liver
biliary system
part of pancreas (uncinate process & inferior head)
what are the foregut-derived glands formed in the dorsal mesentery?
pancreas (superior head, neck, body and tail)
where does the liver develop from?
earliest GI tract associated gland
develops from hepatic bud within ventral mesentery
how much of abdomen does liver occupy during development?
large proportion
what has the greatest impact on foregut region during development?
growth of liver & movement of stomach (& growth of stomach)
What are the peritoneal reflections of the liver?
- bare area (top - area where organ opens up, can put hand around)
- falciform ligament (anterior - ligament attaching liver to ventral body wall)
- lesser omentum (posterior liver)
which part of the liver does not have visceral peritoneum covering? why?
difficult to free liver from diaphragm - doesn’t have visceral peritoneum at surface touching diaphragm, because enclosed by (coronary, left & right triangular ligaments) - consequence of growth and development at the same time of diaphragm, so diaphragm covers bare area of liver
where does the duodenum develop from?
caudal foregut and cranial midgut (has precursors from both sections) - split at bile duct
how does the duodenum develop?
grows rapidly, forming C-shaped loop when stomach rotates
(duodenum was attached to inferior stomach prior anteriorposterior rotation, so when rotated to become oblique, the duodenum forms a C shape bend, which wraps around the head of the pancreas)
how is the lumen of the duodenum throughout development?
lumen is obliterated (from AP rotation of stomach?) and then recanalised (re-opened) by the end of the embryonic period
what does rotation of the stomach do to the duodenum aside from form C-shape around head of pancreas?
pushes duodenum to right, against POSTerior abdominal wall
what are secondarily retroperitoneal structures?
a structure that developed intraperitoneally whose mesentery was lost to fusion with posterior abdominal wall parietal peritoneum due to massive expansion of GI tract during development
what forms in secondarily retroperitoneal structures?
fusion fascia forms (where organ and mesentery was pushed into posterior abdo wall)
what is fusion fascia?
a double connective tissue band derived from the fusion of closely apposed surfaces of peritoneum as a result of degeneration of the lubricating serous layer between them (even visceral peritoneum fuses with posterior abdominal wall)
what can you do to secondarily retroperitoneal structures?
because they were once peritoneal structures and once had mesentery, they can be remobilised (in dissection)
what are examples of secondarily retroperitoneal structures of the foregut?
duodenum (except duodenal cap)
pancreas (head within C-shape of duodenum)
(duodenum pushed out by developing GI and enlarging stomach & liver & rotation of stomach)
