Embrology

Question 1

When is the primitive gut formed and where does it extend from?

how is the gut tube formed?

Answer 1

Week 4

Extends the oropharyngeal membrane to the cloacal memrbrane. lateral folding forms the gut tube and body cavities.

Question 2

Where is the gut derived from?

Answer 2

endoderm

Question 3

What three specific arterial supply match each part of the guy

Answer 3

Foregut- celiac trunk (thoracic aorta for the thoracic foregut)

Midgut- superior mesenteric

Hindgut- inferior mesenteric

All come off the abdominal aorta

Question 4

Structures in the foregut

Answer 4

Artery- celiac

Esophagus

Stomach

1/2nd part of duodenum

Stomach

Liver

Gallbladder

Biliary appartus

Question 5

Structures in the midgut

Answer 5

Arterial supply- superior mesenteric

Duodenum 3rd and 4th part

Jejunum

ileum

cecum

appendix

Ascending colon

transverse colon (proximal 2/3rds)

Question 6

Strucutes in the hindgut

Answer 6

Arterial supply is the inferior mesenteric artery

Distal 1/3 of transverse colon

Descending colon

Sigmoid

Rectum

Anal Canal

Question 7

Why does the stomach have a greater and lesser curve?

Explain the rotation of the stomach

Answer 7

There are differential growths in dvelopment— posterior grows faster

2 rotations

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”

Question 8

The hepatic diverticuulm gives rise to??

Answer 8

The liver and gall bladder and their associated ducts

Question 9

How does the pancreas form?

Answer 9

Develops from the ventral and dorsal bud the evaginate from the gut tube. THe ventral rotates t o fuse to the dorsal

Question 10

what marks the transition from for to midgut? Whats near the transition point

Answer 10

The 1st and 2nd part of the duodenum.

Near the entrance of the bile and pancreatic ducts in the duodenum

Question 11

When and what is midgut herniation

Answer 11

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.

Question 12

What is the end up the hindgut called?

What special seperation happens here?

Answer 12

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

Question 13

What is special about the origin and the epithlium of the anal canal?

Answer 13

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

Question 14

Two important lines in the anal cavity

Answer 14

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

Question 15

How is the mesentery formed and what’s its main purpose?

Answer 15

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

Question 16

Characteristics of the ventral mesentery/mesogastrium

Answer 16

Susepends the foregut from the ventral body wall

Does not extend below the liver

Contributes to the lesser omentum and the falciform ligament

Question 17

Characterisitcs of the dorsal mesentery/mesogastrium

Answer 17

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

Question 18

Explain the creation of spaces in the abdomen

Answer 18

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

Question 19

Answer 19

Question 20

How is the gut tube fixated

Answer 20

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)

Question 21

What is orrphalocele

Answer 21

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

Question 22

What is gastroschisis

Answer 22

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

Question 23

What is illeal (meckel) diverticulum

Answer 23

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

Question 24

What is colonic aganglionsis (hirschsprung disease)

Answer 24

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)