GI Embryology Flashcards
When will the GI tube have a serosa and when will it have an adventitia?
Serosa = intraperitoneal. Adventitia = retroperitoneal.
What embryonic layer in the GI tube is derived from the endoderm?
Epithelial layer of mucosa
What part of the primitive gut tube do the pharyngeal arches come from?
Foregut (pharyngeal foregut goes from oropharyngeal membrane to respiratory diverticulum)
What embryonic layer in the GI tube is derived from the splanchnic mesoderm?
Muscle and connective tissue
What embryonic layer in the GI tube is derived from the neural crest?
Enteric nervous system
What are the boundaries of the foregut?
Oropharyngeal membrane to outgrowth of liver
What are the boundaries of the midgut?
Liver bud to right 2/3 of transverse colon
What are the boundaries of the hindgut?
Left 1/3 of transverse colon to cloacal membrane (future anus)
How does embryonic folding form the gut tube?
Lateral walls bend around to form the longitudinal tube. The caudal and cephalic ends bend around to form the foregut and hindgut. The vitelline duct forms a connection between the midgut and yolk sac.
What is responsible for differentiation of the esophagus & stomach, pancreas, liver, midgut, hindgut and allantois?
Combinations of the different transcription factors seen below.
What is responsible for further differentiation of the different regions of the GI tube?
The gut SHH induces HOX expression in the mesoderm. HOX then dictates how differentiation will proceed.
How does blood supply change in the foregut, midgut and hindgut?
Foregut = celiac artery. Midgut = SMA. Hindgut = IMA.
What is responsible for formation of esophageal stenosis, esophageal sinus and esophageal cyst during development?
Failure of recanalization after the esophageal tube gets filled in. Normally the vacuoles coalesce to form a single, uniform tube. When this doesn’t happen you get stenosis, a sinus, or a cyst.
What are typical presentations when a tracheoesophageal fistula forms with esophageal atresia?
Polyhydramnios, aspiration pneumonia, vomiting and abdominal dissension from air entering stomach.
How does the stomach rotate during development?
LARP: the left side becomes anterior and the right posterior. 1st) 90 degree rotation clockwise 2nd) Caudal end goes up and cephalic end goes down.
How does the midgut develop?
Once the vitelline duct forms, it begins to grow so rapidly that there is no room for it and it herniates through the umbilical cord. 1st, the primary intestinal loop rotates 90 degrees. 2nd, the gut rotates another 180 degrees as it regresses from the umbilical cord. Total rotation ends of being counterclockwise 270 degrees.
What happens if the gut does not rotate 180 degrees as it regresses from the umbilical cord?
Small intestine will be on the right and large on the left.
What happens if the gut rotates the opposite way as it regresses from the umbilical cord?
Duodenum will be anterior to the transverse colon. This will cause atrophy of the large colon beneath it and passing feces will be difficult.
What is the embryologic origin of volvulus?
Failure of fixation of the ascending and descending colons to the dorsal body wall. This allows them to spin around one another.
What happens when the midgut fails to regress from the umbilical cord?
Omphalocoele. This is fixed by slow compression of the omphalocoele over days to weeks back into the abdominal cavity.
What causes gastroschisis?
Failure of abdominal walls to fully fuse.
What are the vitelline duct abnormalities?
Vitelline fistula (fecal discharge through umbilicus), vitelline cysts and Meckel’s diverticulum.
Derivative of hindgut outside of GI tract?
Female urinary bladder and urethra develops as the urorectal septum divides the future bladder from the future anus.
Origin of tissue from the superior region of the pectinate line?
Hindgut. Comes from endoderm, supplied by autonomic nerves and IMA.
Origin of tissue from the inferior region of the pectinate line?
Proctodeum. Comes from ectoderm, supplied by pudendal nerve (sensitive to pain) and internal pudendal artery.
What fistulas can form due to defects in hindgut development?
Urorectal and rectal vaginal fistulas
What causes an imperforate anus?
Failure of recanalization of the cloacal membrane.
