When is the primitive gut formed and where does it extend from?
how is the gut tube formed?
Extends the oropharyngeal membrane to the cloacal memrbrane. lateral folding forms the gut tube and body cavities.
Where is the gut derived from?
What three specific arterial supply match each part of the guy
Foregut- celiac trunk (thoracic aorta for the thoracic foregut)
Midgut- superior mesenteric
Hindgut- inferior mesenteric
All come off the abdominal aorta
Structures in the foregut
1/2nd part of duodenum
Structures in the midgut
Arterial supply- superior mesenteric
Duodenum 3rd and 4th part
transverse colon (proximal 2/3rds)
Strucutes in the hindgut
Arterial supply is the inferior mesenteric artery
Distal 1/3 of transverse colon
Why does the stomach have a greater and lesser curve?
Explain the rotation of the stomach
There are differential growths in dvelopment--- posterior grows faster
1. Rotation of 90degress longitudina;-- what was posterior is now left and what was anterior is now right
2. rotation along the anterior posterior axis-- making the lesser curvature "up"
The hepatic diverticuulm gives rise to??
The liver and gall bladder and their associated ducts
How does the pancreas form?
Develops from the ventral and dorsal bud the evaginate from the gut tube. THe ventral rotates to fuse to the dorsal
what marks the transition from for to midgut? Whats near the transition point
The 1st and 2nd part of the duodenum.
Near the entrance of the bile and pancreatic ducts in the duodenum
When and what is midgut herniation
The midgut herniates through the umbilical cord at week 6-10 of development allowing for rapid growth of the small and large intestines. Midgut rotates 90(around the superior mesenteric artery) then 180 degrees to have everything fit back in the abdomen--this is midgut reduction
otation is counterclockwise and around the axis of the superior mesenteric artery.
What is the end up the hindgut called?
What special seperation happens here?
Cloaca (sewer) and this is where outflow of the GI tract occurs
The urorectal septum grows here forming the rectum and cranial part of the canal dorsal and the urogenital sinus ventral
What is special about the origin and the epithlium of the anal canal?
It has dual origin so there are differences in blood and nerve supply, venus and lymphatic drainage--- important when considering metasis of tumor .
Superior 2/3 from hindgut/endoderm
1. No pain fibers and arise from simple columnar epithelium
2. supplied by the superior rectal artery (from the inferior mesenteric artery).
3. pectinate line marks the junction of hindgut and the proctodeum
The inferior 1/3 of the anal canal is:
1. derived from proctodeum (ectoderm) and stratified squamous epithelium
2. abundant pain fibers
3. supplied by branches of the middle and inferior rectal arteries
Two important lines in the anal cavity
Pectinte line- the end of the original hindgut into the procetodeum
The anocutaneous line- marks the transition of the epithlium from simple to stratified squamous
How is the mesentery formed and what's its main purpose?
2 layers of peritoneium which have fused suspend a portion of the gut tube.
Utilized to send vessels (arteries. veins and lymphatics)
Examples are the lesser omentum, mesoduodenum, mesentery of the sigmoid colon. MOst prominent example is the mesentary of the SI
Characteristics of the ventral mesentery/mesogastrium
Susepends the foregut from the ventral body wall
Does not extend below the liver
Contributes to the lesser omentum and the falciform ligament
Characterisitcs of the dorsal mesentery/mesogastrium
Suspends the fore, mid and hindgut from the dorsal body wall
Contributes to the greater omentum, the mesentery of the SI and the gastrosplenic and splenorenal ligaments
Explain the creation of spaces in the abdomen
1. Digestive tract starts as a simple tube suspended from the body wall by the ventral and dorsal mesogastirums
2. The large open area surronding tube is the primitive peritoneal cavity
3. with rotation of the lesser omentum, the caviity is divided into the lesser and greater sac and communicate by the Epiloic Foramen of Winslow-- located at the right edge of the heptaoduodenal ligament
How is the gut tube fixated
Parts of the dorsal mesentery fuse abdominal structures to the posterior body wall rendering them immobile.
•These structures are considered to be retroperitoneal (i.e. not within the peritoneal cavity.)
•Examples include the ascending and descending parts of the large intestine and part of
the pancreas (which is considered secondarily retroperitoneal)
What is orrphalocele
Congenital abnormalitiy when the midgut loop fails to reduce back into the abdominal cavitiy and stays in the umblical stalk.
Viscera herniate through the umblical rings and has a high (25%) chance of mortality
What is gastroschisis
When the abdominal viscera herinate into the amniotic fluid (generally to the right of the umblicus). Defect in closure of the lateral body and weakness in the anterior wall
Note that it's not through the umblical ring (thats orrphalocele) and not enclosed in a sac of amnion
What is illeal (meckel) diverticulum
Remnant of the viteline duct persists forming a blind pouch antimesenteric border of the ileum... 2 feet from the ileocecal junction, 2 icnhes, and in 2% of the population
What is colonic aganglionsis (hirschsprung disease)
1. results from the failure of neural crest cells
to form the myenteric plexus in the sigmoid colon and rectum.
2. loss of peristalsis and immobility of the hindgut
3. fecal retention
4. abdominal distention of the transverse colon (megacolon)