Embryology of the Gastrointestinal System Flashcards
0
Q
A 22-year-old woman has noted no fetal movement at 17 weeks gestation. A screening fetal ultrasound shows a midline abdominal wall defect, with bowel contents contained within a membraneous sac. Additional diagnostics indicate extensive blood flow to the herniated bowel. Her serum alpha-fetoprotein is increased. What is the diagnosis?
A
omphalocele
1
Q
When does the G.I tract start to develop?
A
A little behind the cardiovascular system in development
2
Q
Regional specification of the gut tube into different components occurs when?
A
As lateral folding brings the 2 sides of the gut tube together
3
Q
The mammalian primitive gut is an epithelial tube surrounded by what?
A
Splanchnic mesoderm
4
Q
As the gut tube matures, what becomes morphologically distinct?
A
Foregut, midgut, and hindgut
5
Q
What does mesoderm of the gut tube mature into?
A
Connective tissue and concentric layers of smooth muscle
6
Q
The enteric nervous system is responsible for innervating what?
A
The smooth muscle to promote contractile movements during digestion
7
Q
The gut differentiates along its ________ axis into distinct ________ organs that have specialized roles in digestion
A
Anterior/posterior (A/P)
Primary
8
Q
The gut organ epithelia acquire distinct _______________ to help carry out their digestive functions
A
Luminal morphologies
9
Q
In general, organs of the foregut do what?
A
ingest food and initiate digestion
10
Q
What generally happens in the midgut?
A
Digestion is completed and nutrients are absorbed
11
Q
What generally happens in the hindgut?
A
Water and ions resorbed and undigested waste is expelled
12
Q
The basic function of the gut can be only accomplished through what?
A
The coordinate function of different tissues and organs that comprise the gut
13
Q
In addition to regionalization, development of the gut tube also involves what?
A
continuous elongation
herniation past the body wall (into the umbilical cord)
rotation and folding for efficient packing
14
Q
The gut tube becomes suspended by what?
A
A 2-layered fold of peritoneum-dorsal mesentery
15
Q
What are mesenteries?
A
Reflection of parietal peritoneum onto the gut tube
16
Q
Most of the gut tube has a _____ mesentery. As part of the development some of the gut will lose it.
A
Dorsal
17
Q
In early development the 2 peritoneal cavities (right and left peritoneal diverticulum) are of _________
A
Equal size
18
Q
In early development the gut tube is a ____________ structure
A
Single midline
19
Q
What are the parts of the foregut?
A
Esophagus stomach and 1/2 duodenum Liver Gall bladder pancreas *spleen
*not part of the gut tube but can treat it as part of the gut tube
20
Q
What are the parts of the midgut?
A
1/2 duodenum jejunum ileum cecum and appendix ascending colon 2/3 transverse colon
21
Q
What are the parts of the hindgut?
A
1/3 transverse colon descending colon sigmoid colon rectum upper part of anal canal
22
Q
What is each gut segment supplied by?
A
An unpaired branch of the abdominal aorta
23
Q
Foregut derivatives are supplied by branches of the _____ artery
A
Celiac
24
Midgut derivatives are supplied by branches of the _______ artery
Superior mesenteric
25
Hindgut derivatives are supplied by branches of the _______ artery
inferior mesenteric
26
How does sympathetic innervation reach the foregut?
The preganglionic cell bodies are T5-T9
The exit the greater splanchnic nerve
Synapse at the celiac preaortic ganglion
Postganglionic axons follow the celiac a.
27
How does sympathetic innervation reach the midgut?
Preganglionic cell bodies are in T9-T12
They exit the lesser splanchnic nerve
Synapse at the superior mesenteric preaortic ganglion
Postganglionic axons follow the superior mesenteric a.
28
How does sympathetic innervation reach the hindgut?
Preganglionic cell bodies are in T12-L2
They exit the least splanchnic nerve
Synapse the inferior mesenteric preaortic ganglion
Postganglionic axons follow the inferior mesenteric a
29
How does parasympathetic innervation reach the foregut and midgut?
Preganglionic cell bodies are from the brainstem
Vagus nerve follows the blood supply to the organs
Location of ganglia: Synapse in the wall of the organs
30
How does parasympathetic innervation reach the hindgut?
Preganglionic cell bodies are S2-S4
Nerves: pelvic splanchnic nerves
Location of ganglia: organ walls
31
What is a lung bud?
An inferior outgrowth off of the esophagus that will form into a lung
32
What divides the lungs from the esophagus during development?
Tracheoesophageal septum
33
What is the separation of esophagus (gut) from respiratory system?
Laryngeotracheal diverticulum (primordium of respiratory system)
34
What is trachoesophageal fistula
Improper connection between trachea and esophagus
35
Esophageal atresia is what type of defect?
Tube of the esophagus is blocked. Loss connection from upper part to lower part of esophagus
36
What is the most common form (95-95%) of tracheoesophageal?
Upper segment of esophagus ending in blind pouch; lower segment originating from trachea just above bifurcation. The two segments may be connected by a solid cord
37
What is esophageal stenosis or atresia?
Narrowed or occluded esophagus due to incomplete recanalization, usually found in lower 1/3
38
What are the majority of esophageal procedures performed in infants/children done for?
Congenital esophageal atresia or acquired caustic strictures
39
Successful esophageal anastomoses may be performed in those few with "_______" esophageal atresia less than ___ cm between the proximal and distal esophageal remnants using various lengthening techniques
Short gap
3
**Note: in the lecture its written opposite but Dr. cole says it this way.....need to check with professor
40
_______ esophageal atresia will require esophageal replacement
Long gap
41
What are the two ways to surgically fix long gap esophageal atresia?
Colon interposition
| Gastric transposition/pullup
42
What is colon interposition?
A section of colon is taken from its normal position in the gut and transposed, with its blood supply intact, into the chest, where it is joined to the esophagus above and the stomach below
43
what is gastric transposition/pullup?
The whole stomach is freed, mobilized and moved into the chest and attached to the upper end of the esophagus
44
When the esophagus spirals, the abnormality is called what?
Corkscrew esophagus
45
What is a congenital esophageal (hiatal) hernia
The upper part of the stomach pushes through the diaphragm and is in the thoracic cavity
46
What can hiatal hernia cause?
Barrett's esophagus: acid backing up from the stomach changes esophagus lining
Predisposes people to esophageal cancer
47
What is esophagitis?
Inflammation caused by acid in stomach
48
Stomach is formed by the ____ of foregut
dilation
49
(Ventral/dorsal) surface grows relatively faster than (ventral/dorsal) surface of the stomach
Dorsal
| Ventral
50
The abdominal esophagus and the stomach start as a _______ suspended by _______ and ______ mesentery
straight tube
| dorsal and ventral mesentery
51
The longer surface of the stomach after 35 days of fetal development rotates to the (right/left)
left
52
Why does the dorsal side cause the stomach to rotate and move to the left during development?
Because the dorsal side of the tube grows rapidly, expands (and runs out of room) and there is a simultaneous clockwise rotation of 90 degrees
53
After rotation, the left side of the stomach now lies (anterior/posterior) and the right side (anterior/posterior)
Anterior
| posterior
54
Because of the rotation of the stomach, the left vagus becomes the (anterior/posterior) vagal trunk and the right vagus the (anterior/posterior) vagal trunk
Anterior
| Posterior
55
What is the most common stomach abnormality?
Pyloric stenosis: overgrowth of the sphincter that allows food to pass from the stomach to the duodenum
56
How long does it take for a newborn to develop pyloric stenosis problems? What are symptoms?
2-3 weeks
Projectile nonbilious vomiting
Small palpable mass at right costal margin
57
What is normal duodenum growth?
Overgrowth of the epithelium: canalize
| Start to open up completely ->normal hollow lumen
58
What is duodenal stenosis and atresia?
Stenosis: doesn't completely reopen
Atresia: Doesn't reopen at all
59
Where is stenosis and atresia most common?
Duodenum and esophagus
60
Partial recanalization in the duodenal can cause what?
Duplication cyst: two separate lumens in the tube
61
The endoderm of the foregut develops into what?
Hepatic diverticulum
62
What does the hepatic diverticulum grow into?
The mesoderm of the septum transversum
63
What forms hepatic sinusoids?
Vitelline system
64
What does the liver divide ventral mesentery into?
Falciform ligament and the lesser omentum
65
Liver congenital malformations are (common/rare)
rare
66
True or False
| All foregut endoderm has the potential to express liver-specific genes and to differentiate into liver tissue?
True
67
Foregut endoderm has the potential to express liver-specific genes and to differentiate into liver tissue, what stops all cells from becoming liver? Where is hepatic development restricted?
Expression is blocked by unknown signals from the trunk mesoderm and ectoderm.
Restrict hepatic development in the posterior endoderm
68
The round ligament of the liver is called what? It also used to be what structure during development?
Ligamentum teres hepatis-fibrous remnant of the umbilical vein
69
What is the bypass for the liver during development?
Ductus venosus
70
The ductus venosus becomes what structure after fetal development?
Ligamentum venosum
71
How does blood bypass the liver in a fetus?
Placenta->left umbilical v. -> ductus venosus -> vena cava
72
What forms the gallbladder and the cystic duct?
cystic diverticulum
73
Where does the bile duct form between?
The developing liver and the foregut (duodenum)
74
What are clinical abnormalities of the gallbladder?
Intrahepatic gallbladder-inside liver
| duplicate or septated gallbladders
75
What is extrahepatic biliary atresia?
Incomplete canalization of the bile duct
76
How common is extrahepatic biliary atresia?
1/15,000 live births
77
What are symptoms of extrahepatic biliary atresia?
Jaundice, dark urine, pale stool - high levels of bilirubin in bloodstream
78
What is the expected survival of infants with extrahepatic biliary atresia?
12-19 months, 100% mortality unless:
| Tx-surgical correction (Kasai's) or transplant
79
What does the pancreas develop from?
Buds in both ventral and dorsal mesenteries
80
What brings the two parts of the developing pancreas together?
The rotation of the stomach
81
What is the most common abnormality of the pancreas?
Annular pancreas
82
What is annular pancreas?
Ventral and dorsal pancreatic buds form a ring around the duodenum
83
What does annular pancreas present as?
Duodenal obstruction. Can cause stenosis or atresia of duodenum
84
During rotation of the foregut, in summary where does everything move?
Stomach moves left
Liver moves right
Relative size of the 2 peritoneal cavities changes
Right side is getting smaller
85
Where can atresias and stenoses occur in the midgut?
May occur anywhere along the intestine
86
Atresias and stenoses in the upper duodenum is usually due to what?
Failure to recanalize
87
Atresias and stenoses occur in areas from the caudal to the duodenum are probably due to what?
Vascular compromise
88
When does rapid growth of the midgut start?
At about 6 weeks
89
What does the rapid growth of the midgut normal produce?
Produces a normal physiologic herniation
90
What kind of herniation happens during midgut development?
Gut loops into the umbilical cord
91
What happens as gut loops into the umbilical cord causing herniation?
The loop rotates 90 degrees counterclockwise around the superior mesenteric a
92
The primary intestinal loop has a cranial end and a caudal end. What does each on differentiate into?
Cranial end: distal duodenum to ileum
| Caudal end: lower ileum to proximal 2/3 transverse colon
93
When does the herniated loops return to the abdominal cavity during development? How much rotation has the loop done?
10th week, 270 degrees total
94
What is malrotation?
When the loops in the herniation only partially rotate and causes an abnormal position of viscera
95
When is malrotation usually presents and what are the symptoms and risks?
Usually presents within first week as duodenal obstruction with bilious vomiting
Increased risk of entrapment of portions of the intestine
Infants-recurrent abdominal pain, intestinal obstruction, malabsorption/diarrhea, peritonitis/septic shock, solid food intolerance, common bile duct obstruction, abdominal distention, and failure to thrive
96
What is volvulus?
Abnormal twisting of the intestine causing obstruction
| Compromises the intestine or the blood flow
97
What is omphalocele? how common is it?
abdominal contents remain herniated into the umbilical cord
Herniation of abdominal contents through enlarged umbilical ring
Pale, shiny sac protrudes from base of umbilical
Mortality rate-25%
Malformations
Cardiac - 50%
Neural tube-40%
Chromosomal 15%
25/10,000 occurence
98
What is Gastroschisis. How often does it occur and why does this defect happen?
ventral abdominal wall defect, abdominal contents herniated into the amniotic cavity
Failure of anterior abdominal wall musculature to close during folding
Gut contents not surrounded by membrane
1-2/10,000 but frequency is increasing in young women (jumps to 26.5/10000)(cocaine??)
Not associated with chromosomal abnormalities or other malformations
Survival rate is excellent
99
What is the vitelline duct?
connects the midgut loop out through the umbilical cord to the yolk sac. When the yolk sac collapse then the vitelline duct should collapse
100
What is ileal (meckel's) diverticulum or fistula?
Remnant of the vitelline duct
outpouching of ileum
proximal to ileocecal valve
101
What is an ileal/vitelline fistula or cyst?
Cyst is a sac that forms in the vitelline and can cause abdominal pain
a fistula is an opening that can have fecal matter leaking out from the umbilical cord
102
How is the majority of the enteric nervous system formed?
Neural crest cells invade the anterior foregut and migrate in a head to tail direction to colonize the entire FG, MG, and HG and give rise to the ENS
103
What is congenital aganglionic megacolon or hirschsprung's disease?
A motor disorder of the colon that causes a functional intestinal obstruction
Without parasympathetic innervation, the colon cannot relax or undergo peristalsis, resulting in a functional obstruction
104
What is hirschsprung's disease related to?
neural crest migration that form the colonic ganglion cells. Both plexuses are affected
105
What is the ratio of occurrence of hirschsprung's disease? (HD)
It occurs in 1/5000 infants with a male to female predominance of 4:1
106
HD can affect what parts of the gut?
It can effect the hindgut and more cranial parts of the gut tube.
70-80% are in the descending and sigmoid colon
1-20% in the transverse colon
3% - entire colon
Decreased occurrence in more proximal parts b.c these are associated with higher mortality rate and/or increased incidence of multiple congenital abnormalities
107
What is the treatment for HD?
Surgery is the only proven, effective treatment for HD
The procedure is called pull-through surgery and involves removing the section of the colon that has no ganglia cells, then connecting the remaining healthy end of the colon to the rectum
108
Rotation, during development, of the hindgut will cause what?
Change the size of the two original peritoneal cavities
Change the anatomical relationship of the organs to one another (no longer a straight tube)
Change (loss) of some of the dorsal mesenteries
Structures will be primarily or secondarily retroperitoneal
109
Define primarily retroperitoneal
Any organ that developed outside the abdominal cavity (kidney) which never had a mesentery to begin with
110
Define secondarily retroperitoneal
Portions of the gut tube whose mesentery has fused with the lining peritoneum
111
Define intraperitoneal
Organs with a mesentery
112
During rotation and herniation of the gut, some parts become pushed back, and become __________ retroperitoneal
Secondarily
113
What does the cloaca develop from?
The hindgut endotherm
114
What is the cloaca divided by? What does the divided cloaca form?
Divided by urorectal septum into urogenital sinus and rectum
115
What is rectourenthral fistula?
Failure of folds to develop in cloaca
116
What type of rectourethral fistula develops in males?
rectoprostatic fistula
117
What type of rectourethral fistula develops in females?
Either rectocloacal canal or rectovaginal fistula
118
What is imperforate anus?
malformation of the anorectal region that may occur in several forms
The rectum may end in a blind pouch that does not connect with the external environment
--or may have openings to the urethra, bladder, or vagina
Stenosis, or narrowing of the anus, or absence of the anus may be present
119
What are imperforate anus symptoms and signs?
Absence or misplaced of anal opening
anal opening very near the vaginal opening in the female
no passage of first stool within 24 to 48 hours after birth
stool passed by way of vagina, base of penis or scrotum, or urethra
abdominal distention
120
Anorectal malformations are spectrum of defects, and are usually referred to as what?
Low or high
121
When anal canal ends as blind sac below the pelvic diaphragm it is:
anal agenesis
122
If rectum ends as blind pouch above the pelvic diaphragm the it is:
anorectal agenesis, most common
