Abdominal Development

Question 1

Primordial gut

Answer 1

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

Question 2

Ventral mesentery gives rise to what?

Answer 2

Lesser omentum and falciform ligament

Question 3

Dorsal mesentry gives rise to what?

Answer 3

Dorsal mesogastrium

Dorsal mesoduodenum

Mesentery proper

Dorsal mesocolon

Question 4

Respiratory diverticulum (lung bud)

Answer 4

Arises around week 4 and forms the tracheoesophageal septum

Question 5

Tracheosophageal septum divides the foregut into what?

Answer 5

Ventral and dorsal sides

Ventral side = respiratory primordium (gives rise to lungs)

Dorsal side = fetal esophagus

Question 6

Stomach development

Answer 6

Week 4, gastric bud appears

Differentiates and grows in 2 axis

Longitudinal and ateroposterior axis

Question 7

Stomach development along longitudinal axis

Answer 7

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

Question 8

Stomach development along the anteroposterior axis

Answer 8

Cephalic pyloric moves right

Caudal cardia moves left

Dorsal mesogastrium lengthens and overlies the developing intestines, ultimately generates the greater omentum

Question 9

Spleen development

Answer 9

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

Question 10

Pancreas development

Answer 10

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

Question 11

Duodenum development

Answer 11

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

Question 12

Liver and gallbladder development

Answer 12

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.

Question 13

Ventral mesogastrium vestigial parts

Answer 13

Falciform ligament, lesser omentum

Question 14

Main pancreatic duct contains what?

Answer 14

Distal dorsal duct and entire ventral duct

Question 15

Accessory duct

Answer 15

Proximal dorsal duct only

Can obliterate occasionally

Question 16

Midgut development week 4-5

Answer 16

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

Question 17

Cephalic limb gives rise to what?

Answer 17

Small intestine

Question 18

Caudal limb gives rise to what?

Answer 18

Large intestine

Question 19

Midgut week 6 development

Answer 19

Rotates Counter clockwise 90 degrees into the umbilical cord.

making the caudal limb left and the cephalic limb right to the SMA

Question 20

Cecum and appendix development

Answer 20

Arises from swelling on caudal limb after rotation into the umbilical cord in week 6

Question 21

Fixation of mesenteries after week 10 of midgut development

Answer 21

Transverse colon fuses with grater omentum

Ascending and descending colons fuse with abdominal posterior wall fascia

Question 22

Midgut in week 10

Answer 22

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

Question 23

Meckels diverticulosis

Answer 23

Malformation caused by vitelline duct persistence

Asymptomatic

Usually located 2 ft from illocecal junction

Question 24

Cloaca

Answer 24

Primitive anorectal canal

Question 25

Cloacal membrane

Answer 25

Endoderm and ectoderm of the hind gut

Question 26

Urorectal septum

Answer 26

Mesoderm that separates the rectum and the urogential sinus

Question 27

Hindgut development

Answer 27

Urorectal septum lengthens and ruptures the cloacal membrane which causes Anal and genital openings and separate systems

Question 28

Anal pit

Answer 28

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

Question 29

Anal canal embrological derivatives

Answer 29

Upper 2/3 anal above the pectinate line is endoderm

Lower 1/3 anal below the pectinate line is ectoderm