Digestive Development + Mesenteries Flashcards
What parts of the gut form from endoderm?
epithelium and glands
What parts form from ectoderm?
epithelium at the cranial and caudal ends via the stomodeal and proctodeal ectoderm, respectively
What forms from the mesoderm?
And from what specific part of the mesoderm?
Splanchnic Mesenchyme forms the muscles, CT and other wall layers
What derives from the foregut?
- Pharynx (primordial) … w/ all related structures
- Lower Respratory System
- Esophagus
- Stomach
- Proximal Duodenum (before bile duct)
- Liver
- Gall Bladder
- Pancreas
PLESPLGP
“Please Plug Up”
Pharynx, Lower resp., Esoph, Stomach, Liver, Gb, Panc
Describe the general process of esophageal development.
- short esophagus elongates rapidly via growth and descent of heart and lungs
- epithelium proliferates and obliterates lumen, but then lumen recanalizes
- 4th pharyngeal arches (IV) > skeletal muscle
- splanchnic mesenchyme > smooth muscle
- all muscles inn. by vagal branches from arch 4
Describe early stomach development (not rotation).
- Slight dilation forms stomach primordium in foregut tube
- Primordium enlarges and broadens ventrodorsally
- Dorsal border grows faster than ventral border, forming greater curvature
What are the mesenteries of the stomach?
Dorsal Mesogastrium - suspends from dorsal abdominal cavity, starts medial but moves left with greater curvature
Ventral mesogastrium - attaches stomach and duodenum to liver + ventral abdominal wall
Describe stomach rotation.
The stomach primordium rotates 90 degrees clockwise around its longitudinal axis (when looking down the length of the embryo in from the head).
- ventral border (lesser curve) moves right, dorsal border (greater curve) moves left
- cranial end (cardia/fundus) moves left and down while caudal end (pylorus) moves right and up
- rotation alters axis of stomach from longitudinal to almost transverse
Describe development of the omental bursa.
- isolated clefts form in dorsal mesogastrium
- clefts fuse to form omental bursa AKA lesser peritoneal sac
- stomach rotation pulls dorsal mesogastrium leftward and enlarges omental bursa
- bursa expands transversely and cranially
- superior part of bursa is cut off by diaphragm to form infracardiac bursa which degenerates usually, but a superior recess persists at the top of the omental bursa
- stomach enlarges and inferior recess forms and then disappears between the layers of greater omentum
How does the omental bursa communicate with the rest of the peritoneal cavity?
via the omental foramen found behind the free edge of the lesser omentum
Describe duodenum development.
- caudal foregut and cranial midgut grow rapidly to create C-shaped loop that projects ventrally
- stomach rotation rotates duodenal loop rightward and retroperitoneally
- lumen is obliterated by epithelial proliferation, then recanalizes
- most of ventral mesentry disappears
Describe development of the liver, gallbladder and bile ducts.
- distal foregut gives outgrowth called hepatic diverticulum
- diverticulum expands into septum transversum (splanchnic mesoderm) which in this area is called the ventral mesogastrium
- diverticulum grows and divides into two parts between mesogastric layers:
- Liver Primordium- endoderm > hepatocytes, mesenchyme > CT elements,cords + sinusesform,hematopoiesis begins
- Gallbladder - caudal diverticulum + its stalk form bladder + cystic duct
What three structures come from the ventral mesentery?
What structure does the ventral mesentery originate from?
What important embryological vessel passes through one of them?
- Lesser Omentum (hepatoduodenal/gastric ligaments)
- Falciform Ligament (liver to ventral abdominal wall)
- Visceral Peritoneum of the Liver
- originates from mesogastrium
- umbilical vein passes through falciform ligament
Describe development of the pancreas.
- Dorsal and Ventral Pancreatic Buds arise from caudal foregut
- smaller ventral bud develops near entry of bile duct > duodenum, larger dorsal develops more cranially + behind
- ventral bud gives uncinate process and part of head, dorsal bud gives rest
- ventral bud duct + distal dorsal bud duct form main pancreatic duct, proximal dorsal bud duch forms accessory
- as stomach rotates, pancreas is pulled back to lie along dorsal abdominal wall
Describe spleen development.
- stomach rotates, bringing the mesogastrium leftward to fuse with suprarenal peritoneum (splenorenal ligament)
- mesenchymal cells between layers of this left part of the dorsal mesogastrium give rise to spleen
- fetal splenic lobules exist which disappear before birth, but leave notchs on spleen’s superior border
- spleen functions in hematopoiesis until late fetal stages
What derives from the midgut?
- small intestine distal to bile duct opening
- cecum
- appendix
- colon (up to 1/2 - 2/3 across the transverse)
What artery supplies midgut derivatives
superior mesenteric artery and its branches
What is the smaller ‘loop’ that forms in the more cranial embryological GI tract?
Ansa Duodenalis
- a loop of GI tract that projects ventrally into the septum transversum
- composed of superior horizontal and descending duodenum
What is the larger loop that forms from the more caudal embryological GI tract?
ansa umbilicalis (AKA Midgut Loop)
- from the inferior horizontal duodenum to the greater riolan anastamosis
- extends towards the yolk sac/omphaloenteric duct
Describe the changes that occur in the ansa umbilicalis to form the intestines.
- the ‘cranial limb’ of the loop grows rapidly, forming the small intestines
- the ‘caudal limb’ grows less, just giving the cecal swelling
Describe rotation of the midgut loop/ansa umbilicalis.
- the midgut loop rotates 90 degrees CCW within the umbilical cord around the axis of the superior mesenteric artery
- because of this rotation, the cranial limb moves right and caudal limb moves left
Describe retraction of the midgut loop
- enlargement of abd. cavity allows return of midgut loop
- SI returns first, posterior to sup. mesenteric a.
- LI returns next, and rotates 180 degrees CCW more
Describe development of the cecum and appendix.
- cecal swelling appears on caudal limb of midgut loop
- apex of swelling grows slower than rest, forming an appendicular diverticulum
- appendix increases in length from distal cecum
- uneven postnatal cecal growth brings the appendix up onto the cecum’s medial side
What are the derivatives of the hindgut?
- Transverse Colon (only left 1/3 - 1/2)
- Descending Colon
- Sigmoid Colon
- Rectum
- Anal Canal (superior part)
- Bladder/Urethra Epithelium
What artery supplies all hindgut derivatives?
inferior mesenteric artery
What is the expanded terminal part of the hindgut called?
What is it?
Cloaca
- an endoderm-lined cavity
- connects to ectoderm via cloacal membrane (cloaca > anal pit)
What are the names of the primordial mouth and anus, respectively?
Stomodeum
Proctodeum
What does the anal canal develop from?
2 sources
What structure separates the two?
superior 2/3 - hindgut
inferior 1/3 - anal pit
- pectinate line at the bottom of the anal valves separates epithelium derived from the 2 different sources
