Severson: Gastrointestinal System Flashcards
The developing gut can be divided into the…
foregut
midgut
hindgut
What binds the cephalic end of the gut?
oropharyngeal membrane
What binds the caudal end of the gut?
cloacal membrane
The lining of the digestive system and its related gland develop from…
endoderm
The stomodeum and the proctodeum are lined by…
ectoderm
Skeletal muscle of the oropharynx and upper esophagus are derived from…
brachial arch mesoderm (4th and 6th arches)
Smooth muscle and CT of the GI tract develop from…
splanchnic mesoderm
The nervous component of the GI tract develops from…
Neural crest cells that migrate into the developing GI tract
What innervates the left colic flexure?
Vagus nerve (parasympathetic)
What innervates all but the left colic flexure?
pelvic splanchnic nerves (parasympathetic)
What is esophageal stenosis?
Narrowing d/t incomplete recanalization of the esophagus during development (epithelial cells persist)
What causes esophageal atresia?
Defective tracheoesophageal septum
What causes polyhydraminos?
esophageal atresia and stenosis (regurgitation and choking after birth when drinking milk)
What is tracheoesophageal fistula?
incomplete separation of the trachea from the esophagus (defective tracheoesophageal septum) that can lead to respiratory distress
What is a congenital hiatal hernia?
If the esophagus fails to lengthen the stomach can be drawn up into the thorax
What is the blood supply to the foregut? Midgut? Hindgut?
celiac artery (except pharynx and esophagus)
Superior mesenteric aretery
Hindgut Inferior mesenteric artery
How does the parasympathetic nerve supply differ between the three parts of the primitive gut?
foregut and midgut = vagus
hindgut= pelvic splanchnic
pharnyx, esophagus, stomach, upperduodenum, glands of pharyngeal pouches, thyroid, respiratory tract, liver, gallbladder and pancreas come from what part of the primitive gut?
foregut
Lower duodeum, jejunum, ileum, cecum, appendix, ascending and R1/2, and transverse colon come from waht part of the primitive gut?
midgut
The L 1/2 of the transverse colon, descending colon, sigmoid colon, rectum and superior anal canal come from what part of the primitive gut?
hindgut
What suspends the distal esophagus, stomach and proximal duodenum from the dorsal wall?
dorsal mesentery
The ventral mesentery is derived from…
the transverse septum
What connects the distal esophagus, stomach and proximal duodenum to the ventral wall?
Ventral mesentery
What encircles the liver and forms its visceral peritoneum?
ventral mesentery
What forms the lesser omentum?
Ventral mesentery between the stomach and first part of the duodenum
What forms the falciform ligament?
ventral mesentery between the liver and the ventral body wall
What passes in the free border of the falciform ligament?
umbilical vein
What important rotation occurs in the GI tract during development?
90 degree rotation of the stomach brings the GREATER CURVATURE to the left and the LESSER CURVATURE to the right
What becomes the ventral surface of the stomach and what nerve supplies it?
original left side
left vagus nerve
What becomes the dorsal surface of the stomach and what nerve is it supplied by?
Original right side
right vagus nerve
What forms the greater omentum?
Dorsal mesentery (grows rapidly and enlarges the omental bursa which is eventually obliterated)
What forms the gastrocolic ligament?
Dorsal mesogastrium and the transverse mesocolon fused together
Where is the gastrocolic ligament located?
between the stomach and the transverse colon
Where does the spleen develop?
Dorsal mesentery
What leads to the formation of the gastrosplenic and splenorenal ligaments?
rotation of the stomach brings the spleen to the left and forms the ligaments
Describe the fxn of the spleen.
- hematopoietic cell development during fetal life
2. Can revert to hematopoiesis in the adult (extramedullary myelopoiesis)
What causes pyloric stenosis?
hypertrophy of hte circular layer of stomach smooth muscle at the pyloric outlet–> narrowing of the pyloric canal
A male infant has a distended stomach and is projectile vomitting.
Pyloric stenosis
What causes intestinal atresia and stenosis?
- failure of recanalization of the intestine (usually duodenum)
- lumen occluded by INTESTINAL EPITHELIAL CELLS
A pt w/ intestinal atresia and stenosis usually has…
vomit containing bile
What occupies a large portion of the ventral mesentery?
The liver derived from ENDODERM of the foregut grows into the ventral mesentery and teh mesenchyme of hte transverse septum
What gives rise to the hepatic cells and bile ducts draining hte liver?
hepatic diverticulum
What gives rise to the fibrous capsule and connective tissue of the liver?
transverse septum
What develops from the endodermal hepatic diverticulum?
gallbladder w/ the cystic duct and ventral pancreas
What is a site for hematopoietic tissue during fetal development prior to splenic hemopoiesis?
liver
What is extrahepatic biliary atresia?
Rare
can occur when the bile duct fails to canalize–> infant becomes JAUNDICED
What does the pancreas develop from?
ventral and dorsal pancreatic buds that grow out from the dorsal and ventral walls and into the dorsal and ventral mesenteries
The ventral pancreatic bud is derived from…
hepatic diverticulum
Because the stomach and duodenum rotate to the right what happens to the pancreas?
ventral pancreas and common bile duct end up BEHIND where they fuse w/ the DORSAL PANCREAS in the dorsal mesentery
The duct of the dorsal pancreas fuses with the…
duct of the ventral pancreas
What becomes the definitive pancreatic duct?
Duct of the ventral pancreas (dorsal degenerates)
What are acini in the pancreas?
exocrine pancreas (develop from terminal ends of the duct system)
What gives rise to the endocrine pancreas?
budding of cells from the ducts
You see a pt with pancreatic tissue in the wall of the stomach, duodneum and ileal diverticulum. What causes this?
Accessory pancreatic tissue occurs b/c the pancreatic tissue develops from ENDODERMAL EPITHELIUM of the developing GI tract
What is attached at the apex of the midgut loop, bewteen the cephalic and caudal limbs of the loop?
omphaloenteric duct (yolk stalk)
What happens to the omphaloenteric duct in an adult?
if present, it’s located 2 ft cranial to the ileocecal jxn and may form an ileal diverticulum
When does herniation of the developing intestine into the umbilical stalk occur?
6th or 7th week b/c of rapid intestinal growth and limited space in the abdominal cavity d/t large size of the liver and kidneys
When does the intestine return to the abdominal cavity?
10-11 weeks
Cephalic limb of midgut loop grows rapidly and forms the small intestine, while caudal limb undergoes little change. Rotation of the midgut loop with the small intestine returning first forces the distal colon to the left.
What supplies the midgut and serves as a pivot point for a counter clockwise rotation (270 degrees) of the caudal midgut limb around the cephalic midgut limb to bring the colon across the small intestine?
superior mesenteric artery
What happens to the cecum when the colon return to the abdominal cavity?
it goes to the lower right quadrant
When does heterotopic gastric mucosa and pancreatic tissue occur?
when cells lining the stomach or pancreatic tissue develop at sites OTHER than the stomach
What is an ileal diverticulum? Greater prevalence in M or F?
present in 2 to 4 per cent of people and is 3 to 5 times more common in MALES than females.
A Meckel diverticulum is a persistence of the proximal part of the YOLK STALK (duct) (omphaloenteric duct). The diverticulum can become inflamed.
May end as a blind pouch, be attached to the umbilicus by a fibrous cord or a fistula (omphaloenteric fistula), or result in a condition known as volvulus (twist around) that can lead to ischemia or strangulation of the bowel.
May be sight for ectopic stomach tissue and pancreatic tissue
What causes a congenital omphalocele?
failure of the intestinal loops to return from the umbilical cord to the abdominal cavity during the 10th week and the ventral abdominal wall to close.
Herniated loop covered by amnion (epithelium of the umbilical cord).
What causes a congenital umbilical hernia?
the ventral abdominal musculature fails to close the umbilical ring.
Protruding mass is covered by subcutaneous tissue and skin
What causes gastroschisis?
a defect near the median plane of the right ventral abdominal wall. The cause of gastroschisis is uncertain, but may be due to ischemic injury to the anterior abdominal wall
What causes non-rotation of the midgut?
the caudal limb returns to the abdomen first, and the small intestine lies on the right side of the abdomen and the large intestine on the left.
What forms the mesentery and attaches all of the intestine to the posterior abdominal wall?
dorsal mesentery
The greater omentum, transverse mesocolon and sigmoid mesocolon are all derivatives of..
dorsal mesentery
What causes the duodenum and ascending/descending colons to be retroperitoneal?
dorsal mesentery fusing w/ the peritoneal lining of the dorsal body wall
What serves as the caudal end of the hindgut and the base of the urogenital sinus?
cloaca
What separates the cloaca from the proctodeum?
cloacal membrane
What divides the cloaca into a urogenital sinus and rectum/anal canal?
uroretal spetum
What divides the cloacal membrane into a urogenital area and an anal area?
cloacal membrane
What forms in the area where the urorectal septum approaches the cloacal membrane that is in the process of undergoing apoptosis?
perineal body
What is derived from the upper 2/3s and lower 1/3 of the hindgut?
upper 2/3- anal canal
lower 1/2- proctodeum
What is the site of the ANAL MEMBRANE and is where the endoderm of the hindgut becomes continuous w/ the ectoderm of hte proctodeum?
pectinate or anorectal line
How do the arterial/venous systems differ for the hindgut and proctodeum?
hindgut- inferior mesenteric
proctodeum- inferior rectal branch of the internal pudendal
lymphatics from the hindgut drain to…
inferior mesenteric nodes
lymphacts from the proctodum drain to…
superficial inguinal nodes
What is an anocutaneous line?
where the anal epithelium changes from simple columnar to stratified squamous
What is a congenital megacolon (hirschsprung’s disease)?
absence of parasympathetic ganglia in the wall of the colon d/t failure of NCC to migrate into the splanchnic mesoderm
What causes an imperforate anus?
persistence of the cloacal (anal) membrane to atresia (anal atresia) of the anal canal/rectum.
What are hindgut fistulas?
Connect the hindgut with the vagina (rectovaginal fistula), urethra (rectourethral fistula), or the bladder (rectovesical fistula).
What causes a hindgut fistula?
Occur because of incomplete division of the cloaca by the urorectal septum into the rectum/anal canal and urogenital sinus.
