Lecture 3: Development of the Digestive Sytem Flashcards
1
Q
The epithelium of the digestive system is made up of what kind of ‘derm; what are the exceptions?
A
Endoderm
*except mouth (1st arch portion) and anal canal = ECTODERM*
2
Q
The smooth muscle, vasculature, CT, and any cells arising from monocytes are made up of what kind of ‘derm?
A
Mesoderm: splanchnic mesoderm
3
Q
The autonomic ganglion, post-ganglionic neurons, in the digestive tract arise from which cell type?
A
Neural Crest
4
Q
What are the boundaries of the foregut, midgut, and hindgut?
A
- If above the yolk sac, then it’s foregut
- Same level as yolksac, is migut
- Below yolksac, is hindgut
5
Q
What are the derivatives of the Foregut; arterial suppky?
A
- Pharynx
- Respiratory system
- Esophagus
- Stomach
- Liver and Pancreas
- Biliary apparatus
- Proximal duodenum
*CELIAC TRUNK*
6
Q
What are the derivatives of the Midgut; arterial supply?
A
- Small intestine (duodenum)
- Cecum and veriform appendix
- Ascending colon
- Right 1/2 of transverse colon
*SUPERIOR MESENTERIC ARTERY*
7
Q
What are the derivative of the hindgut; arterial supply?
A
- Left 1/2 of transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Superior anal canal
- Epithelium of urinary bladder/urethra
*INFERIOR MESENTERIC ARTERY*
8
Q
What’s a Tracheoesophageal (TE) Fistula; which week does this occur?
A
- Abnormal migration of the tracheoesophageal folds and formation of the septum = abnormal passage between trachea and esophagus
- Commonly associated w/ esophageal atresia.
- Occurs during WEEK 5
9
Q
What are the presenting signs and symptoms of TE fistula?
A
- Prenatally: polyhydramnios
- Birth: coughing, gagging, cyanosis, vomiting, voluminous oral secretions, possible respiratory distress
10
Q
What is shown in this picture, and what can this tell you?
A
- This image shows coiling of a NG tube within the esophagus.
- This indicates an infant has a TE Fistula
11
Q
What week does the stomach begin to rotate and explain what occurs.
A
- Week 4
- At the start the ventral border is to the right and dorsal border is to the left
- Dorsal wall grows much faster and forms the greater curvature, while the ventral wall forms the lesser curvature
- Stomach will rotate 90° clockwise about a longitduinal axis, the left side is now ventral, while the right is now dorsal.
12
Q
What occurs to the left and right vagal nerves during developmental stomach rotation?
A
- Left vagal nerve becomes anterior
- Right vagal nerve becomes posterior
13
Q
When the stomach does 90° of clockwise rotation about the longitudinal axis, what space forms?
A
The lesser sac (omental bursa)
14
Q
What is Hypertrophic Pyloric Stenosis; common presenting sx?
A
- Narrowing of pyloric lumen obstructing food passage due tp hypertrophy of the muscularis externa in this region.
- Immediate post-feeding vomiting that is nonbilous and forceful (projectile vomiting), fewer and smaller stools, failure to gain weight or weight loss
15
Q
Explain the formation of the liver and biliary system.
A
- All form from a single diverticulum of gut endoderm
- Endoderm differentitates into hepatocytes, bile ducts, and hepatic ducts
16
Q
What happens as the gallbladder begins to elongate; what forms?
A
Forms the cystic duct and where the cystic and hepatic ducts merge forms the common bile duct.
17
Q
Explain formation of the pancreas
A
- Develops from 2 distinct buds, dorsal and ventral primordia
- Dorsal forms the body and tail
- Ventral forms the head and uncinate process
- As duodenum rotates to the right, ventral pancreatic bud is carried dorsally
18
Q
Where do the 2 pancreatic ducts arise from?
A
- Main pancreatic duct arises from ventral primordia
- Towards tail pancreatic duct comes from the dorsal primordia
19
Q
What is Annular pancreas; when would bilious vomit be seen?
A
- Bifed ventral pancreatic bud will grow out and fuse around the duodenum, causing an obstruction (narrowing).
- If annulus develops inferior to bile duct, child will have sx’s similar to pyloric stenosis, EXCEPT, the vomit will be bilious
- If obstruction is superior to bile duct, vomit will be non-bilious
20
Q
Any accessory pancreatic ducts arise from which part?
A
Dorsal pancreatic bud
21
Q
Explain the rotation of the midgut; how much rotation occurs?
A
- Due to limited size of the abdomen, lengthening midgut herniates out into umbilicus at 6 weeks, rotating 90°.
- Comes back in during week 10 and rotates 180°
- Total of 270° rotation
22
Q
What do the cranial and caudal ends of the gut form at the end of midgut rotation?
A
- Cranial forms the small intestine
- Caudal forms the large intestine
23
Q
What is Omphalocele; occurs when?
A
- Weeks 6-10
- Herniated bowel does not fully retract back into the abdomen, will be covered w/ an amnion and peritineum membrane
24
Q
What is Gastroschisis; occurs when?
A
- Week 4
- Herniation of abdominal contents due to muscular defect in anterior abdominal wall.
25
What is embryologic mechanism of Hirschsprung Disease (aka megacolon)?
- Most common neonatal obstruction
- Failure of NC to migrate
- Lack autonomic ganglion cells (from **NC**) distal to dilated segment: area cannot relax is always constricted
- Enlarged section is normal
26
What is nonrotation of the midgut?
- Completes first 90° CCW rotation but does not do remaining 180° CCW rotation
- Ends up with left-sided colon and rightsided small intestines
- Pt's may have obstructions
27
What is reversed rotation of the midgut?
- Completes initial 90° CCW but then does a 180° CW rotation
## Footnote
- Transverse colon ends up posterior to the duodenum, normally the duodenum is posterior to the transverse colon
28
Explain formation of the definitive gut lumen
- Start with hollow gut tube (**week 6**),
- Gut tube is then occluded by endodermal proliferation
- Apoptosis (recanalization) occurs and by **week 8** you have now formed the definitive hollow gut.
29
What 2 defects can occur during formation of the definitive gut lumen?
1) Duplication - pocket forms in wall of the gut tube
2) Incomplete recanalization = stenosis typically seen in 3rd part of duodenum
30
What is Meckel's Diverticulum, can lead to?
- Abnormality of the **vitelline duct** (normally regresses)
- Projection from the ilium to the abdominal wall
- Can lead to intestinal obstruction, GI bleeding, bowel sepsis
31
What is the rule of 2's for Meckel's Diverticulum?
- 2% of population
- Found 2 feet from ileocecal junction
- Usually about 2 inches long
- 2 types of ectopic tissues: gastric and pancreatic
- 2:1 ratio of male to female
32
What is a Omphalomesenteric fistula?
- Persistent attachment of vitelline duct to umbilicu, fistula causes poop to leave out of bellybutton
33
What 'derm layers are the cloacal membrane and urorectal septum composed of?
Cloacal membrane = Endoderm and Ectoderm
Urorectal septum = mesoderm
34
What does the urorectal septum do; what happens to the cloacal membrane?
- Migrates down and partitions cloaca into a dorsal anorectal canal and a ventral urogenital sinus.
- Cloacal membrane ruptures thereby opening both the UG sinus and anal canal to the exterior
35
How do parts of the anal canal differ; what separates the anal canal?
- The anal canal is seprated into 2 distinct parts, one from the hindgut endoderm and the anal pit from ectoderm, separated by the **pectineal line**
- Each part has a separate blood and nerve supply
36
What is the neurovasculature of the hindgut endoderm in anal canal?
- Nerves: Autonomic
- Blood vessels: Inferior mesenteric/superior rectal a.
- Lymphatics: Inferior mesenteric lymph nodes
37
What is the neurovasculature of the hindgut ectoderm of the anal canal?
- Nerves: Somatic nerve --\> **P**udendal. **P**ainful hemorrhoids
- Blood vessels: Iliac --\> middle and inferior rectal
- Lymphatics: Meets at pectineal line. Superior inguinal lymph nodes
38
What is underlying cause of these Anorectal Malformations in figures A and B?
A) Proctodeum did not form correctly
B) Proctodeum did not migrate at all
39
What is the underlying cause of the Anorectal Malformations seen in figures D and H?
Urorectal septum abnormally divided the tract
40
Differentiate between the pleuropericardial membrane, the pleuroperitoneal membrane and the septum transversum.
- Pleuropericardial folds migrate to midline and are separated from pleural canals by the pleuropericardial folds
- Septum transversum meets with the pleuroperitoneal membranes and fuses.
- Tissue from the body wall is then pulled into the diaphragm
\***left fuses more slowly\***
41
How does the diaphragm form?
- Septum transversum with the central tendon
- Dorsal mesentary becomes the right and left crus of the diaphragm
- Peripheral musculature gets pulled off body wall
42
What is shown here and how does this occur, what side does it usually occur on?
- Congenital diaphragmatic hernia
- Defective formation and/or fusion of the pleuroperitoneal membrane, large opening in posterolateral diaphragm (**foramen of Bochdalek)**
- 85-90% occur on the left side
43
What is Mesentery?
- Double layer of serous membrane from splanchinc mesoderm
- Allow BV's, nerves, and lymphatics to get to an organ and then back to the body wall.
- Has a parietal and visceral layer
44
In the Abdominal cavity and liver what does the: dorsal mesogastrium, ventral mesogastrium, and ventral mesentery form?
Dorsal mesogastrium - greater omentum (around stomach)
Ventral mesogastrium - lesser omentum (stomach to liver)
Ventral mesentery - falciform ligament (liver to abdominal wall)
45
What are the mesenteries of the mid/hindgut; are they from ventral or dorsal?
- Mesoduodenum - mesentery around duodenum
- Mesentery proper - containing jejunum and ileum
- Mesocolon - around transverse colon and sigmoid colon
- Mesorectum - mesentery around the rectum
\*ALL from DORSAL\*
46
What is the axis of rotation of the midgut?
Superior Mesenteric Artery!!!
47
What are the divisions of the Dorsal mesogastrium?
- Splenorenal (leinorenal) ligament
- Gastrolienal ligament
- Greater omentum
48
How is the greater omentum formed?
- As the stomach migrates and rotates, the dorsal mesogastrium is pulled down and rotated
- You now have fusion of 2 double layers (4 total) of splanchic mesoderm, creating the greater omentum
49
What does fusion of mesenteries with body walls result in?
Secondary Retroperitoneal structures
50
Which structures become secondary retropeitoneal?
- Mesogastrium dorsal to spleen (part holding pancreas)
- Mesoduodeum
- Ascending mesocolon
- Descending mesocolon
51
What does it mean for a structure to be intraperitoneal; what are the intraperitoneal structures?
- Anything surrounded by mesentery
- Stomach
- Tail of pancrea
- 1st part of duodenum
- Jejunum, ileum
- Transverse Colon
- Sigmoid Colon
52
We have a mneomic for retroperitoneal structures, using it, indicate which structures are primary and secondarily retroperitoneal?
SADPUCKER
S - suprarenal glands (primary)
A - aorta and IVC (primary)
D - duodenum 2nd-4th part (secondary)
P - pancreas, except tail (primary)
U - ureters (primary)
C - colon, ascending/descending (secondary)
K - kidneys (primary)
E - esophagus (primary)
R - rectum (primary)
