2.2 - development of the peritoneum & foregut (embryo) Flashcards
what does embryonic folding achieve in terms of GI development?
- get a ventral body wall
2. get a gut within a cavity
what does lateral embryonic folding achieve (for GI)?
- creates ventral body wall
2. primitive gut becomes tubular
what does craniocaudal embryonic folding achieve (for GI)?
creates cranial & caudal pockets from yolk sac endoderm (2 blind ends, closed off by membranes & 1 opening (umbilicus))
what do the foregut and hindgut begin as?
blind diverticular (blind end tubes)
how is the midgut different from the foregut and hindgut?
has an opening at first (umbilicus) and is continuous with the yolk sac (the whole gut tube is pinched off form the yolk sac from folding)
what is the implications of the embryonic divisions?
blood supply & lymphatic drainage in adult depends on embryonic origin
where does the primitive gut tube run?
from stomatodeum (depression on cranial part of future mouth) rostally to proctodenum (future anus) caudally with opening at umbilicus
what is the internal lining of the primitive gut tube derived from? what does it become?
endoderm
future epithelial lining
where does the external lining of the primitive derive from? what does it become?
derived from splanchnic mesoderm
becomes future musculature & visceral peritoneum
what is the primitive gut tube suspended in? by what?
suspended in intraembryonic coelom (between splanchnic & somatic mesoderm)
by a double layer of splanchnic mesoderm (folding causes double layer - from pinching off yolk sac)
what are the foregut adult derivatives?
oesophagus, stomach, pancreas, liver, gall bladder, duodenum (proximal to entrance of bile duct)
what are the midgut adult derivatives?
duodenum (distal to entrance of bile duct) jejunum, ileum cecum ascending colon proximal 2/3 transverse colon
what are the hindgut adult derivatives?
distal 1/3 transverse colon descending colon sigmoid colon rectum upper anal canal internal lining of bladder & urethra (out of bladder)
what is the point which divides foregut and midgut in adults?
the entrance of bile duct into the duodenum
where does each embryonic segment receives its blood supply from?
a distinct branch of the abdominal aorta
what are the main branches of the abdominal aorta?
celiac trunk
superior mesenteric artery
inferior mesenteric artery
what does the celiac trunk supply (section)?
unpaired vessel supplying foregut
what does the SMA supply (section of embryo)?
midgut - unpaired vessel
what does the IMA supply (embryo section)?
a little section of midgut, mostly hindgut
what do structures which develop close to the junction between foregut and midgut have?
mixed blood supply
what is the blood supply to the duodenum (proximal to entry of bile duct)? branch of?
gastroduodenal artery & superior pancreaticoduodenal artery (of coeliac trunk)
what is the blood supply to the duodenum (distal to entry of bile duct)? what is it branch of?
inferior pancreaticoduodenal artery (branch of superior mesenteric artery)
what is the blood supply to the head of the pancreas?
superior pancreaticoduodenal artery (CT) and inferior pancreaticoduodenal artery (SMA)
what do the somatic and splanchnic mesoderm go onto become?
somatic (top) - body
splanchnic (bottom) - viscera
where is the intraembryonic coelom?
between somatic and splanchnic mesoderm
post lateral folding, becomes space around suspending (splanchnic mesoderm) gut tube
how does the intraembryonic coelom begin?
as one large cavity (entire length of developing embryo)
what happens later on to intraembryonic coelom?
subdivided by future diaphragm into abdominal and thoracic cavities
what does the peritoneal membrane line?
the abdominal cavity and invests the viscera
what happens to the peritoneal cavity during development?
it grows, changes shape and specialises
what does the peritoneum invest?
dorsal & ventral body wall & primitive gut tube (peritoneum = abdominal cavity)
what is the peritoneal ‘cavity’?
a potential space
under normal conditions, what does the peritoneal cavity contain?
should contain nothing, only serous fluid to ensure structures can move smoothly over each other
what are the mesenteries?
a double layer of peritoneum suspending the gut tube from the abdominal wall
where do the mesenteries run?
entire length of the posterior (dorsal) body wall
what is the purpose of the mesenteries?
- allow a conduit for blood and nerve supply
- allow mobility where needed
(way in and out of GI tract, allow arterial supply to access newly developed structures)
what is the new primitive gut suspended within?
the intraembryonic coelom by splanchnic mesoderm (inner) - wraps around gut to tube to form mesenteries (double layer from lateral folding)
how does the mesentery form? (suspending gut tube)
mesentery formed from a condensation of the (double layer of) splanchnic mesoderm
what causes dorsal and ventral mesoderm?
folding of the double layer of splanchnic mesoderm
what does dorsal mesentery suspend?
the entire gut tube from the dorsal body wall
where is the ventral mesentery present?
only in the region of the foregut
what is the function of the dorsal and ventral mesenteries in the region of the foregut?
to divide the cavity into left and right sacs in this region only
what does the left sac contribute to?
greater sac
what does the right sac become?
lesser sac
where is the lesser sac situated?
lies behind the stomach (potential sac behind the stomach)
what do midgut and hindgut have in terms of sac?
only have dorsal mesentery, so 1 continuous sac - no ventral mesentery
what are omenta?
specialised regions of peritoneum
what is the greater omentum formed from?
dorsal mesentery
when is greater omentum seen?
first structure seen when the abdominal cavity is opened anteriorly
what is the lesser omentum formed from?
ventral mesentery
what do the free edge of the lesser omentum conduct?
the portal triad
what is the portal triad?
part of the hepatic lobule (liver), consists of: proper hepatic artery proper hepatic vein common bile duct lymphatic vessels branch of vagus nerve
where does the greater omentum extend from?
large fold of visceral peritoneum hanging from greater curvature of stomach, passes anterior to small intestines and reflects on itself to ascend to transverse colon to reach posterior abdominal wall
where does the lesser omentum extend?
from lesser curvature to 1st part of duodenum to inferior surface of liver all the way up to anterior abdominal wall
