Ga2 - Gi Development

Front 1

GI tract can be nicely divided up into what 3 parts and where exactly are they?

Back 1

•GI tract can be nicely divided up into the foregut, midgut and hindgut

•Foregut = oral cavity down to the 1st part of the duodenum
•Dividing point for foregut and midgut is the papilla in the duodenum (ampulla of Vater) that receives the outflow of the liver and the pancreas

•Midgut = from papilla to middle of transverse colon

•Hindgut = middle of transverse colon to everything downstream

Front 2

Origins of Different Components of Gut Tube - origins of luminal lining epithelium, resident cells, auerbach and meissner's plexus, and lymphoid tissue

Back 2

-Luminal Lining Epithelium from ENDODERM

-Resident Cells in lamina propria, submucosal CT, muscularis externa, and adventital CT from splanchnic MESODERM

-Myenteric (Auerbach’s) plexus and Submucosal (Meissner’s) plexus from NEURAL CREST. (Autonomic Innervations for secretions and motor actiity in the wall of the gut tube)

-Lymphoid tissue, e.g. GALT, from bone marrow (mesoderm)

Front 3

Origins of Components of Liver, Pancreas, and Gall Bladder - endoderm and mesoderm derive what? What are the origins of CT and blood vessels in the liver?

Back 3

-Hepatic parenchymal cells, pancreatic acinar cells, islet tissue, luminal lining of gall bladder from ENDODERM.

-CT in capsules and rest of organ, blood vessels, smooth muscle in wall of gall bladder from MESODERM.

-In liver, CT and blood vessels from SEPTUM TRANSVERSUM, rest from splanchnic MESODERM

Front 4

Divisions of Primitive Gut Tube

Back 4

-Foregut: from buccopharyngeal membrane to anterior intestinal portal

-Midgut: from anterior to posterior intestinal portal

-Hindgut: from posterior intestinal portal to cloacal membrane

Front 5

The buccopharyngeal membrane blocks what?

Back 5

Buccopharyngeal membrane blocks the entrance to the oral cavity early in development that eventually degenerates to connect oral cavity to pharynx

Front 6

The cloacal membrane blocks what?

Back 6

Cloacal membrane blocks the connection between the rectum and anus, also degenerates later to establish connection

Front 7

Blood Supply to Embryonic Divisions of Gut Tube

Back 7

-Lower foregut: Celiac Trunk

-Midgut: Superior Mesenteric Artery

-Hindgut: Inferior Mesenteric Artery

Front 8

Cranial Foregut Derivatives

Back 8

-Epithelium lining posterior oral cavity
-Thyroid epithelium
-Respiratory diverticulum
-Epithelium of auditory tube -Epithelium of palatine tonsils
-Epithelium of parathyroids
-Epithelium of thymus

Front 9

Caudal Foregut Derivatives

Back 9

-Oropharynx and Esophagus
-Stomach
-First part of duodenum
-Liver, pancreas, and gall bladder

Front 10

Midgut Derivatives

Back 10

-Second part of duodenum
-Ileum and jejunum
-Cecum and vermiform appendix
-Ascending colon
-Transverse colon to middle

Front 11

Hindgut Derivatives

Back 11

-Second half of transverse colon
-Descending colon
-Sigmoid colon
-Rectum
-Anus to anal valves (pectinate line)

Front 12

Hindgut Derivatives - Anal canal is derived from? What will you find above and below the pectinate line?

Back 12

•The anal canal is actually derived from both endoderm and ectoderm

•In anal canal, the pectinate line is a place where cloaca used to be

•Above the pectinate line, you will find mucosa that is colonic, below the line you will find mucosa that is similar to the cells of the body surface (stratified squamous)

Front 13

Cloaca - receives outflow of what 2 systems, cloaca is divided into what 2 things by what

Back 13

-Latin word for sewer is cloaca

-This primitive portion of posterior hindgut receives outflow of GI tract and urogenital system

*Urorectal Septum divides cloaca into Rectum and precursor of Urinary Bladder

-Covered more extensively with urogenital development

Front 14

Gastric Rotation - stomach forms from dilation of what? has which 2 mesogastrium? (mesogastrium the developmental term for each of the mesenteries that support the developing gastrointestinal tract)

Back 14

-Stomach forms from dilation of caudal foregut (at the end of esophagus)

-Has both dorsal and ventral mesogastrium

-From the dorsal mesentery, the abdominal aorta comes down and branches to supply this organ

Front 15

Gastric Rotation - first rotation carries what to where, forming what as a result?

Back 15

-First Rotation carries dorsal mesogastrium from dorsal to ventral, elongating it extensively to form Greater Omentum

-dorsal side of stomach is now becoming ventral by rotating 90 degrees

Front 16

Gastric Rotation - second rotation brings what two things of the stomach where? These 2 rotations create what as a result?

Back 16

-Second Rotation brings cardiac stomach to down and to left, pyloric up and to right

-These 2 rotations create the normal anatomical orientation of the stomach and origin of other organs such as the spleen (which is in dorsal mesentery).

Front 17

Hepatic Development - What else forms from caudal foregut besides stomach? What does this formation grow into (2)

Back 17

-Liver Diverticulum forms from caudal foregut

-Liver diverticulum grows into surrounding splanchnic mesoderm and septum transversum and branches

Front 18

What are branches of the liver diverticulum called and what do they form (2)?

Back 18

-Branches are called hepatic cords and form ducts and hepatic parenchymal cells

-CT and blood vessels in liver from splanchnic mesoderm and septum transversum

Front 19

Proximal part of diverticulum will form...

Back 19

-Proximal part of diverticulum will form the gall bladder, the ventral and dorsal buds of the pancreas and liver diverticulum

-While these forming, the stomach is rotating – changing orientations of these other organs-->ex(the dorsal and ventral pancreatic buds will then fuse and create the 2 lobes of pancreas)

Front 20

Details of Hepatic Development - What is the major function of the liver before the bone marrow takes over? Because of this function, what happens to the liver, and consequently the peritoneal cavity and midgut loop?

Back 20

-Liver is major Hematopoietic Organ before bone marrow takes over this function

-Result is an extraordinarily large liver

-Restricts volume of peritoneal cavity, so midgut loop undergoes much of its formation in extraembryonic coelom (physiological herniation)

Front 21

Gall Bladder Development - what forms the gall bladder and where does it branch off from? What do the endoderm and mesoderm form here?

Back 21

-Cystic Diverticulum (precursor of gall bladder) branches off hepatic diverticulum

-Luminal epithelum from endoderm

-Mural structures from splanchnic mesoderm

Front 22

Pancreatic Development - what 2 buds form the pancreas and how?

Back 22

-Ventral Pancreatic Bud forms adjacent to cystic diverticulum

-Ventral pancreatic bud branches

-On opposite side, Dorsal Pancreatic Bud forms

-Dorsal (main body and tail) and ventral buds then fuse (head)

Front 23

Origins of Pancreatic Exocrine Cells - what forms from endoderm and mesoderm?

Back 23

-Pancreatic acinar cells and luminal lining of ducts from endoderm

-Capsule, CT, blood vessels, etc. from splanchnic mesoderm

Front 24

Origins and Secretions (2) of Islets of Langerhans

Back 24

-Controversial

-Some evidence that they arise from neural crest

-Other evidence suggests origin from endoderm

-Unknown in humans

•Islets of Langerhans (endocrine portion) secrete insulin and glucagon

Front 25

Rotation of Midgut Loop - In Toto (in its entirety), midgut loop undergoes how big of a rotation? The axis of rotation is formed by what duct and artery?

Back 25

-Due to the fact that the liver takes up 80% of peritoneal cavity, there is no room for midgut development--> midgut loop forms U-shaped loop and herniates out into umbilical cord

-Midgut loop is initially short, but undergoes extensive elongation, looping, and rotation

-In Toto, midgut loop undergoes a 270 degree counterclockwise rotation

-Axis of rotation is formed by vitelline duct and superior mesenteric artery

Front 26

Rotation of Midgut Loop - First 90 degree counterclockwise rotation occurs as midgut loop grows into what? What is this process called?

Back 26

-First 90 degree counterclockwise rotation occurs as midgut loop grows into extraembryonic coelom

-This is called Physiological Herniation of midgut loop

Front 27

Rotation of Midgut Loop - Second 180 degree counterclockwise rotation occurs as what is reduced and midgut loop goes where?

Back 27

-Second 180 degree counterclockwise rotation occurs as herniation is reduced and midgut loop returns to peritoneal cavity

Front 28

Results of Midgut Rotation - what can happen to parts of midgut loop after rotation via mesentaries? What ends up in the RLQ? What happens to the ascending and descending colon?

Back 28

-As midgut loop is reduced into peritoneal cavity, parts of it become attached to body wall by resportion of mesenteries

-Also, cecum, vermiform appendix, and first part of ascending colon end up in right lower quadrant of abdomen

*Ascending and descending colon become Secondarily Retriperitoneal

Front 29

Peritoneal Status of GI organs (Retroperitoneal (3) vs. Intraperitoneal (10) and organs associated with each)

Back 29

-Retroperitoneal Viscera: (never in peritoneal cavity) esophagus to diaphragm and rectum

-Intraperitoneal viscera: (always projecting into peritoneal cavity) abdominal esophagus, some of gall bladder, stomach, some of duodenum, jejunum, ileum, cecum, vermiform appendix, transverse colon, sigmoid colon

Front 30

Definition of Adventitia and Serosa. Which one does retroperitoneal organs have and which one does intraperitoneal organs have?

Back 30

-Adventitia is CT that binds to the exterior of an organ

-Serosa is adventitia that is covered by mesothelium

-Retroperitoneal organ have an adventitia but no serosa while intraperitoneal organs have serosa

Front 31

Peritoneal Status of GI Organs - Secondarily Retroperitoneal Viscera and 4 associated organs

Back 31

Secondarily Retroperitoneal Viscera: (transitiently “in” peritoneal cavity but outside peritoneal cavity in adult) - most of duodenum, most of pancreas, ascending colon, descending colon.

a secondarily retroperitoneal structure migrated and is now fixed after being intraperitoneal during embryological development.

Front 32

What 2 things lead to the Formation of Complete Rectum and Role of Pectinate Line. Rectum forms from the...

Back 32

-Upper endodermally derived rectum fuses with lower ectodermally derived rectum to form the complete rectum

-Pectinate line (series of little folds in mucosa) divides the 2 embryologically - different parts of rectum

The rectum forms from the cloaca

Front 33

Differences between upper and lower rectal cancer: pain in upper rectal cancer? how can lower rectal cancer be determined?

Back 33

-Upper rectal cancer will be painless b/c the mucosa is insensitive

-Lower rectal cancer can be determined by examining superficial inguinal nodes

Front 34

Septation of Caudal Hindgut: Urorectal Septum divides what into what 2 parts? What does this mean in terms of the derivations of the 2 divisions?

Back 34

-Urorectal Septum divides cloaca into rectum and urinary bladder

-Thus, upper rectum and urinary bladder derived from endodermally derived epithelium

Front 35

Septation of Caudal Hindgut: Anus forms from what?

Back 35

-Anus forms from ectodermally derived Anal Pit

-Pectinate Line is approximate boundary between two rudiments

Front 36

Embryology of Rectoanal Canal - what is found above pectinate line and what is found below it?

Back 36

-Above pectinate line, endodermally derived epithelium, autonomic innervation (insensitive mucosa), superior rectal artery and vein, inferior mesenteric nodes

Front 37

Embryology of Rectoanal Canal - what is found below pectinate line?

Back 37

-Below pectinate line, ectodermally derived epithelium, inf. rectal nerve (sensitive mucosa), inferior rectal artery and vein, superficial inguinal nodes


A hole lies between the two types of surfaces that the pectinate line forms, which disappears and becomes the anus.

Front 38

Endodermally-derived portions receive what kind of innervation from where?

Ectodermally-derived portions drain to what lymph nodes?

Back 38

-The endodermally-derived portions receive sensory innervation from the autonomic nervous system. Its mucosa is insensitive to pain.

-The ectodermally-derived portions drain to lymph nodes such as the superficial inguinal lymph nodes. This has important clinical correlations for colorectal cancer.

Front 39

Where do surgeons look if the cancer is above the pectinate line versus if its below the pectinate line? What provide landmarks to determine which nodes to explore during cancer surgery?

Back 39

-Exploratory surgery looks for lymph nodes infiltrated by cancer. If the cancer is above the pectinate line, surgeons look for inferior mesenteric lymph nodes, which are not found easily. If below, surgeons look for superficial inguinal lymph nodes, which are easier to find.

-Folds around the pectinate line provide landmarks to determine which nodes to explore during cancer surgery.

Front 40

What kind of epithelium is found above and below the white line in the anal canal?

Back 40

-There is stratified squamous epithelium up to the white line in the anal canal. Above the white line, there is simple columnar epithelium.

Front 41

Embryology of Rectoanal Canal - carcinoma in upper part versus lower part. Where is the rectoanal junction?

Back 41

-Carcinoma in upper part painless, check inferior mesenteric nodes for metastasis

-Carcinoma in lower part painful, check superficial inguinal nodes for metastasis

-Rectoanal junction (simple columnar to stratified squamous keratinized) at white line (of Marshall)

Front 42

Congenital Defects -Ileal (Meckel) Diverticulum - frequency of this defect in humans, result of what which leaves behind what?, found where, symptoms?, may contain what that leads to ulceration?, correctable?

Back 42

*Most common defect, occurs in 2% of humans

-It is the result of the vitelline duct and yolk sac not degenerating completely—which leaves behind a remnant of the vitelline duct.

-Found in Middle of midgut-Ileum*

-Usually Asymptomatic*

-May contain Ectopic Gastric Mucosa -> ulceration

-Usually surgically correctable

Front 43

Congenital Defects - Omphalocele: defect where and why, frequency in humans, fixed how?

Back 43

Defect in anterior abdominal wall covered by peritoneum and amnionic sac - Failed Reduction, 1/5000-1/10,000 births

Omphalocele is shown here, as one can see a cystic structure around the umbilicus. This herniated sac herniates out of the body wall (into the peritoneal cavity and umbilical sac).
-It is fixed after removal of the umbilical cord.

Front 44

Congenital Defects - Gastroschisis - defect where and why

Back 44

Rare defect in anterior abdominal wall without peritoneal and amnionic covering - Lateral Fold Defect

-Can be fixed

Front 45

Congenital Defects - Congenital megacolon (Hirschsprung disease): events that lead to symptoms (3), what plexus can become defective, how is it fixed?

Back 45

-Failed NC migration to colon -> poor peristalsis -> colonic dilation (upstream from aganglionic segment)

-Congenital megacolon can result in a defective myenteric plexus because of the aganglionic surface of the colon. Because of the lack of neural crest cells during development, there is a defective Auerbach's/myenteric plexus.

-There is no myenteric plexus in the area indicated by the arrow. This is surgically corrected by removing the aganglionic tissue.