Abdominal Development Flashcards
Primordial gut
Gut tube that originates from the oropharyngeal membrane to the cloacal membrane.
Originally starts closed cranial at oropharyngeal membrane and closes at the caudal end once it meets with cloacal membrane
Ventral mesentery gives rise to what?
Lesser omentum and falciform ligament
Dorsal mesentry gives rise to what?
Dorsal mesogastrium
Dorsal mesoduodenum
Mesentery proper
Dorsal mesocolon
Respiratory diverticulum (lung bud)
Arises around week 4 and forms the tracheoesophageal septum
Tracheosophageal septum divides the foregut into what?
Ventral and dorsal sides
Ventral side = respiratory primordium (gives rise to lungs)
Dorsal side = fetal esophagus
Stomach development
Week 4, gastric bud appears
Differentiates and grows in 2 axis
Longitudinal and ateroposterior axis
Stomach development along longitudinal axis
Rotates 90- degrees clockwise making the right side the left side and the left side the right side now.
Posterior wall grows faster than the anterior causing the greater curvature vs the lesser curvature
Pulls dorsal mesogastrium towards the left via 90 degree longitudinal rotation and creates the omental bursa behind the stomach
Stomach development along the anteroposterior axis
Cephalic pyloric moves right
Caudal cardia moves left
Dorsal mesogastrium lengthens and overlies the developing intestines, ultimately generates the greater omentum
Spleen development
5th week, primordial appears de novo via mesoderm proliferation within the dorsal mesogastrium
Pulled left by rotations of stomach and fuses with the peritoneum of the posterior wall
Also fuses with left kidney and stomach via splenorenal and gastrosplenic ligaments respectively
Pancreas development
2 buds: 1 dorsal mesogastrium and 1 ventral mesogastrium
Ventral bud rotates dorsally w/ duodenum rotation. Causes fusion of ventral and dorsal bud and forms the uncinate process and part of the heat and the main pancreatic duct.
Dorsal bud forms the neck and tail of the pancreas and accessory duct
Duodenum development
Week 4: forms in foregut and midgut
Rapid growth and rotation of stomach forms C-shape loop to right.
Attached to pyloris of the stomach
Most of the ventral mesentery disappears at this time except the duodenal cap (explains why the proximal duodenum is intraperitioneal)
Weeks 5-6 = profliferation, obliteration of lumen and recanalization
Liver and gallbladder development
Hepatic diverticulum outgrows from the distal foregut and penetrates into the septum transversum and grows rapidly.
The connection to the duodenum (foregut) narrows and forms the Bile duct which is posterior in adults due to rotation of duodenum
Bile duct forms a ventral outgrowth that forms the gallbladder and cystic duct.
Ventral mesogastrium vestigial parts
Falciform ligament, lesser omentum
Main pancreatic duct contains what?
Distal dorsal duct and entire ventral duct
Accessory duct
Proximal dorsal duct only
Can obliterate occasionally
Midgut development week 4-5
Primary intestinal loop forms and rotates around the SMA
Has two limbs: cephalic (Small) and caudal (Large)
Cephalic limb forms rapidly and coils where as the caudal does not.
Cephalic limb starts superior to SMA and the caudal limb starts inferior to SMA
Cephalic limb gives rise to what?
Small intestine
Caudal limb gives rise to what?
Large intestine
Midgut week 6 development
Rotates Counter clockwise 90 degrees into the umbilical cord.
making the caudal limb left and the cephalic limb right to the SMA
Cecum and appendix development
Arises from swelling on caudal limb after rotation into the umbilical cord in week 6
Fixation of mesenteries after week 10 of midgut development
Transverse colon fuses with grater omentum
Ascending and descending colons fuse with abdominal posterior wall fascia
Midgut in week 10
Intestinal loop returns to the abdominal cavity via 180 degree counter clockwise turn
- puts the caudal end in right position
- Puts the cranial end in left position
Also causes dorsal mesentery to twist around SMA
Meckels diverticulosis
Malformation caused by vitelline duct persistence
Asymptomatic
Usually located 2 ft from illocecal junction
Cloaca
Primitive anorectal canal
Cloacal membrane
Endoderm and ectoderm of the hind gut
Urorectal septum
Mesoderm that separates the rectum and the urogential sinus
Hindgut development
Urorectal septum lengthens and ruptures the cloacal membrane which causes Anal and genital openings and separate systems
Anal pit
Surface ectoderm and proctoderm proliferates and invaginate within the ruptured cloacal membrane around week 7 (due to programmed apoptosis)
Unties the superior and inferior anal canals
Anal canal embrological derivatives
Upper 2/3 anal above the pectinate line is endoderm
Lower 1/3 anal below the pectinate line is ectoderm
