Embryology IV- GI Development Flashcards
1
Q
Name the following contributions to the foregut:
1) blood supply
2) sympathetic innervation
3) parasympathetic innervation
4) postganglionic sympathetic cell bodies
A
1) celiac artery
2) greater thoracic splanchnic nerves (T5‐T9).
3) vagus
4) celiac and superior mesenteric ganglia
2
Q
Name the following contributions to the midgut:
1) blood supply
2) sympathetic innervation
3) parasympathetic innervation
4) postganglionic sympathetic cell bodies
A
1) superior mesenteric artery
2) lesser thoracic splanchnic nerves (T10‐T11)
3) vagus
4) celiac and superior mesenteric ganglia
3
Q
Name the following contributions to the hindgut:
1) blood supply
2) sympathetic innervation
3) parasympathetic innervation
4) postganglionic sympathetic cell bodies
A
1) inferior mesenteric artery
2) lumbar splanchnic nerves (L1‐ L2)
3) pelvic splanchnic nerves
4) inferior mesenteric ganglia
4
Q
Name the 8 adult derivatives of the foregut
A
pharynx esophagus stomach duodenum (1st and 2nd parts) liver pancreas gallbladder biliary apparatus
5
Q
Name the 7 adult derivatives of the midgut
A
doudenum (2nd, 3rd, and 4th parts) jejunem ileum cecum appendix ascending colon transverse colon (proximal 2/3rds)
6
Q
Name the 5 adult derivatives of the hindgut
A
transverse colon (distal 1/3rd) descending colon sigmoid colon rectum anal canal (above pectineal line)
7
Q
The boundary between foregut and midgut is marked by what?
A
the ampulla of Vater (major duodenal papilla)
8
Q
What is the ampulla of Vater?
A
The common path where the common bile duct and main pancreatic duct enter the 2nd part of the duodenum
9
Q
The boundary between midgut and hindgut is marked by what?
A
splenic flexure
10
Q
What part of the gut is most commonly associated with pathology?
A
midgut
11
Q
The lining of the entire gut tube is derived from what?
A
endoderm
12
Q
The wall of the gut tube (smooth muscle, connective tissue, vasculature, etc.) is derived from what?
A
mesoderm
13
Q
What adult derivatives have portions that arise from different portions of the gut and where do they come from?
A
1) duodenum- the first part and the 1⁄2 of the second part of the duodenum develop from foregut. The remainder of the duodenum develops from midgut. Transition at major duodenal papilla
2) The large intestine develops in part from the midgut and in part from the hindgut.
14
Q
When does primitive gut formation begin?
A
beginning of week 4
15
Q
What does the primitive gut tube develop from?
A
Lateral body folds form on both sides of the flattened trilaminar disc, and include all three germ layers (ectoderm, mesoderm, and endoderm). Over about one week, the folds continue moving ventrally and eventually fuse in the anterior midline at the linea alba, forming a cylindrical trunk. As the folds move ventrally, the upper endoderm lined part of the yolk sac gets pinched off and internalized. The part of the yolk sac that is captured by the lateral body foldings forms the primitive gut tube and is fully lined by endoderm
16
Q
What part of the yolk sac is maintained in the midgut region during lateral folding and the formation of the primitive gut tube?
A
vitelline duct
17
Q
The little bit of extraembryonic space around the primitive gut tube that gets captured during lateral body folding becomes fully enclosed to become what?
A
the embryonic coelom
18
Q
The embryonic coelom forms what cavities?
A
the pleural, pericardial, and peritoneal cavities. (by septation)
19
Q
The initial forming of the anterior and posterior recesses that will become the foregut and hindgut (as well as the gap between the two that will become the midgut) is formed by what?
A
head-to-tail body foldings (these occur at the same time as lateral foldings)
20
Q
During head-to-tail body folding, can the midgut still communicate with the rest of the yolk sac (through the vitelinne duct)? When does this end?
A
Yes. Around the 8th‐9th weeks of development, the vitelline duct will pinch off and close, and the remainder of the yolk sac is discarded.
The vitelline duct will be incorporated into the umbilical stalk.
21
Q
The parietal and serous layers of peritoneum that line the abdominal cavity are derived from what?
A
lateral plate mesoderm (between the parietal layer that spans the entire 360 surface of the abdominal wall and the serous layer lie the peritoneal cavity)
22
Q
What suspends the primitive gut tube from the dorsal and/or ventral body walls during development?
A
a (minimally) double‐layered reflection of visceral peritoneum called a mesentery
A mesentery that attaches to the dorsal body wall is called a dorsal mesentery. A mesentery that attaches to the ventral body wall is called a ventral mesentery
23
Q
What portion(s) of the gut have dorsal and ventral mesentery?
A
only the foregut. The midgut and hindgut only have dorsal mesenteries
24
Q
What is an intraperitoneal organ?
A
These are covered on all sides by visceral peritoneum and is suspended out into the abdominal cavity via a mesentery. These viscera are highly mobile
25
What is a retroperitoneal organ?
One that is wedged between the body wall and the parietal layer of peritoneum. As such it is only covered on one side by parietal peritoneum and has no contact with the visceral peritoneum. Most retroperitoneal viscera are found pushed up against the dorsal body wall and are largely immobile.
26
Name the intraparitoneal organs of the abdomen
- stomach,
- first part of the duodenum (aka cap or bulb),
- jejunem, ileum, cecum, -transverse and sigmoid colon,
- tail of pancreas,
- liver, gallbladder, spleen
remember that intraperitoneal organs are covered on all sides by visceral peritoneum and is suspended out into the abdominal cavity via a mesentery. These are highly mobile
27
Name the retroparitoneal organs of the abdomen
```
S- suprarenal gland
A- abdominal aorta and IVC
D- doudenum (2nd-4th parts)
P- pancreas (head, neck, and body- NOT tail)
U- ureters
C- colon (descending and ascending)
K- kidneys
E- esophagus
R-rectum
```
28
What develops within/from the ventral embryonic mesentery?
the liver, gallbladder and the biliary duct system. Therefore, the two adult mesenteries attached to the adult liver are derived from the ventral embryonic mesentery. These are the falciform ligament (between liver and anterior body wall) and the lesser omentum (between liver and stomach).
The liver develops from an endodermal bud off the developing foregut within the ventral embryonic mesentery.
29
What does the falciform ligament contain? What is it the remnant of?
the round ligament of the liver (ligament trees)- the adult remnant of the fetal umbilical vein
30
What ligaments comprise the lesser omentum?
the hepatogastric ligament (between liver and the lesser curvature of the stomach) and the hepatoduodenal ligament (between liver and the 1st part of the duodenum).
31
What does the hepatoduodenal ligament convey?
the portal triad (proper hepatic artery, hepatic portal vein, and common bile duct).
32
Where does the dorsal embryonic mesentery span?
from the primitive gut tube (stomach, specifically) to the dorsal body wall
33
What develops within/from the dorsal embryonic mesentery?
the spleen (also, the gastrosplenic ligament (between spleen and the greater curvature of the stomach) and the splenorenal ligament)
NOTE: spleno= lieno
34
What is the only foregut viscera that develops from mesoderm?
the spleen
**IMPORTANT**
35
What does the splenorenal ligament contain?
It contains the splenic vessels, as well as the tail of the pancreas.
36
What ligaments comprise the greater omentum?
The gastrosplenic, gastrocolic, and gastrophrenic ligaments
37
What rotation does the foregut undergo?
90 degree clockwise rotation (to the right). As a consequence of this rotation, the ventral embryonic mesentery containing the liver will move from the 6:00 position to the 9:00 position, so that the liver is now occupying the upper right quadrant. The dorsal embryonic mesentery containing the spleen (and pancreas) will move from the 12:00 position to the 3:00 position, so that the spleen is now occupying the upper left quadrant. The stomach will occupy a midline position still, but rotated 90 degrees.
38
What happens to the pancreas as a result of the 90 degree rotation of the foregut?
Most of the pancreas (which develops in the dorsal embryonic mesentery) gets pushed up against the dorsal body wall and become retroperitoneal. The exception is the tail of the pancreas which is contained within the splenorenal ligament.
39
How does foregut rotation cause the formation of the lesser and greater peritoneal sac?
As the ventral embryonic mesentery and the liver rotate to the right, a part of the peritoneal cavity is captured between the posterior aspect of the stomach and the dorsal body wall forming a cul‐de‐sac. This space is the lesser sac or omental bursa. The greater sac refers to the remainder of the peritoneal cavity. The communication between the greater and lesser sacs is the epiploic foramen (of Winslow). This opening is just posterior to the hepatoduodenal ligament.
40
During 90 degree rotation of the stomach, the anterior surface of the stomach becomes what?
the lesser curvature (the original posterior surface then becomes the greater curvature)
41
Does the epiploic window lie posterior or anterior to the the hepatoduodenal ligament?
posterior
42
What is the anterior border of the omental bursa?
stomach and lesser omentum
43
What is the posterior border of the omental bursa?
the aorta, pancreas and left kidney
44
What three visceral systems develop as buds from the endodermal lining of the developing foregut?
the lungs and lower respiratory tract, liver and biliary tract, and the pancreas. (**Remember, the spleen is unique, it developed from mesoderm**).
The lungs and lower respiratory tract develop from an endodermal bud off the esophageal region. The liver and pancreas develop from endodermal buds off the duodenal region.
45
How do the lungs and lower respiratory tract begin their development?
from a single respiratory diverticulum off the endodermal lining of the esophagus beginning in the 4th week
46
What quickly happens to the respiratory diverticulum?
This diverticulum quickly bifurcates into a double bud that will form the lungs and right and left respiratory trees. 12‐14 further divisions occurs over the course of several weeks of development to develop an elaborate respiratory tree.
47
The 25th‐28th week is a critical time line for what? Why?
the development for the respiratory system. Infants born prior to the 25th week have little chance for survival. Before the 25th week, the type I and type II (surfactant) pnuemocytes are not adequately developed to allow gas exchange.
48
There originally is an open communication between the developing respiratory and gastrointestinal systems. The communication is closed by the formation of what?
the trachoesophageal septum which will separate the foregut from the trachea.
49
What does the trachoesophageal septum arise from?
from mesoderm
50
What is the most commonly occurring newborn defect of the respiratory system?
tracheoesophageal fistula. This occurs when the TE septum forms incorrectly
51
What is esophageal atresia?
The most common TE fistula where the proximal esophagus ends in a blind pouch. The distal portion of the esophagus is usually connected to the trachea near the carina.
52
Esophageal atresia is characterized by what?
polyhydramnios (too much amniotic fluid) during fetal life, since the defect will interfere with the ability of the fetus to swallow amniotic fluid.
53
What happens during feeding in a patient with esophageal atresia?
The newborn will immediately regurgitate when he attempts the first feeding. The milk will simply ooze right back out after it reaches the blind sac.
NOTE: this is not projectile vomiting.
Even more distressing, when the newborn burps, gastric contents may be refluxed into the tender newborn lungs. This is repaired surgically as quickly as possible, to avoid damage to the lungs and ensure adequate nutrition.
54
How does the pancreas develop?
from the endodermal lining of the duodenal region of the gut tube via the dorsal and ventral pancreatic buds in the 5th – 6th weeks.
55
How does the ventral pancreatic bud develop during the 5th and 6th weeks?
it originates in the ventral embryonic mesentery, but rotates posteriorly around the duodenum, coming to lie posterior to the dorsal pancreatic bud, where the two fuse together.
56
What does the ventral pancreatic bud give rise to?
It gives rise to the head and uncinate process of the pancreas.
57
How does the dorsal pancreatic bud develop during the 5th and 6th weeks? What does it give rise to?
It originates in the dorsal embryonic mesentery, and remains in place and elongates after fusing with the ventral bud. It gives rise to the neck, body, and tail of the pancreas.
58
Which pancreatic bud makes the main pancreatic duct?
both contribute to its formation.
NOTE: the main pancreatic duct joins the common bile duct to enter into the 2nd part of the duodenum at the ampulla of Vater
59
What is the most common developmental defect of the pancreas?
annular pancreas
60
What happens in annular pancreas?
the ventral pancreatic bud splits in two and part rotates dorsal to the duodenum while the other part rotates ventral to the duodenum The end result is a collar of pancreatic tissue that surrounds the duodenum, leading to obstruction (atresia).
61
What in annular pancreas characterized as clinically?
Annular pancreas is characterized clinically by polyhydramnios during fetal life, and by projectile vomiting (bile‐stained) upon feeding in the newborn.
62
T or F. The liver, gallbladder, and biliary tract develop from an endodermal bud off the duodenal region of the foregut.
T.
NOTE: liver defects are rare
63
What are the 5 major consequences of foregut rotation?
1) stomach changes position
2) formation of omental bursa (lesser peritoneal sac)
3) positioning of liver, spleen, and pancreas
4) postnatal components of the dorsal and ventral embryonic mesenteries
5) formation of C-shaped duodenum
64
Rotation/herniation of the midgut occurs when?
6th-10th weeks
65
At the onset of development, the midgut takes the form of a simple U‐shaped loop, with cranial and caudal limbs arranged around the longitudinal axis of the SMA. What will the cranial loop form?
the proximal part of the midgut (duodenum, jejunum, and proximal ilium)
66
At the onset of development, the midgut takes the form of a simple U‐shaped loop, with cranial and caudal limbs arranged around the longitudinal axis of the SMA. What will the caudal loop form?
the distal ileum through the splenic flexure of the transverse colon
67
How does rotation of the midgut begin?
rotation begins with a 90 degree counterclockwise rotation of the caudal limb around the axis of the SMA. The cranial loop is now to the right of the SMA, and the caudal loop is to the left.
The beginning of this rotation is coincident with the beginning of the herniation event (6th week).
68
When does the remaining 180 degrees of rotation of the midgut take place?
10th week of development (as the midgut is retracted back into the abdominal cavity.)
69
Describe the events of the final 180 degree rotation of the midgut during the 10th week of development
1) As the midgut returns to the abdominal cavity in the 10th week, the remaining 180 degrees of counterclockwise rotation is completed.
2) The jejunum (cranial limb) returns first, and lies to the upper left side of the abdomen. The ileum follows, and lies to the lower right side of the abdomen.
3) The cecum enters last, and passes to the upper right aspect of the abdominal cavity, before descending to the lower right quadrant.
4) The descent of the cecum pulls the transverse colon across the upper abdomen and the ascending and descending colons settle on the right and left sides of the posterior abdominal wall, respectively.
70
What are the two important newborn defects related to the herniation of the midgut?
These are omphalocele and gastroschisis. Both of these are types of anterior body wall defects.
71
What is Omphalocele?
results from a failure in retraction of the herniated gut tube. It gets captured in the umbilical stalk, and the newborn presents with coils of intestine protruding through the umbilical ring. **The intestines will be covered by a sac of amnion**
These herniations can be quite large, and may involve stomach and liver in addition to the intestine. There is a high degree of mortality associated with defect because it usually occurs in common with other cardiovascular or nervous system defects.
72
What is Gastroschisis?
a defect of the lateral body foldings, most commonly involving the right side near the site of the original right umbilical vein. This vein obliterates during development, leaving an inherent weakness in the abdominal wall, just to the right of the umbilical ring.
The newborn presents with coils of intestine protruding through the abdominal wall to the side of the umbilical ring. **In this case, the intestines are not covered by a sac of amnion**.
This is usually not life‐threating and is corrected surgically, although, the coils of the intestine cannot be returned all at once. They must be protected, and are usually returned slowly, as the abdomen grows.
73
Gastroschisis and Omphalocele are BOTH associated with what?
elevated maternal a-fetoprotein (AFP) levels
74
What is volvolus?
Volvolus is a type of malrotation that results in abnormal twisting of the gut tube and alterations in the definitive positions of the abdominal viscera.
75
What are the are two communications between the developing GI tract and the umbilicus?
the vitelline duct and the allantois
76
What does the vitelinne duct connect?
connects the midgut with the umbilicus
77
What does the allantois connect?
connects the cloaca (future bladder) with the umbilicus
78
Which closes first, the vitelinne duct or the cloaca?
The vitelline duct usually closes somewhere around the 8th ‐10th weeks. The allantois should close about a week or so later
79
What is the adult remnant of the allantois?
the urachus (median umbilical ligament) which spans between the apex of the bladder and the anterior abdominal wall.
80
What is the most common developmental defect of midgut?
Meckel’s diverticulum
81
What is Meckel's diverticulum and what causes it?
Meckel’s diverticulum occurs when a proximal portion of the vitelline duct remains patent after the distal part obliterates. This results in a small, blind pouch attached to the small intestine, usually in the ileal region.
The diverticulum may become infected or ulcerated because it may contain ectopic gastric or pancreatic tissue. These are described as being found in 2% of the population, ~ 2 inches long, and located ~ 2 feet from the ileocecal junction (Rule of 2’s).
82
What is Vitelline fistula?
occurs when the vitelline duct remains patent at birth. This will form a direct communication between the lumen of the midgut and the exterior of the body at the umbilicus. It is characterized by the oozing of meconium from the umbilical stump of the newborn.
83
Notes on vitelline cysts
Vitelline cysts can occur as isolated regions of patency anywhere along the length of the vitelline duct
84
What is Urachal fistula?
Occurs when the allantois remains patent at birth. This will form a direct communication between the bladder (developed from the cloaca) and the exterior of the body at the umbilicus.
It is characterized by the oozing of urine from the umbilical stump of the newborn.
85
What are Urachal cysts?
refer to isolated patencies somewhere along the length of the urachus. This may be closer to the body wall, closer to the bladder, or somewhere in the middle. There is usually no leakage of urine at the umbilical stump with these defects.
86
What is Urachal diverticuli?
may develop later in life in regions where the allantois scarred down but did not seal tightly.
Conditions that result in increases in urethral pressure (prostatic disease), raise urinary pressure in the bladder and may cause the layers to separate and dilate.
87
What is hypertrophic pyloric stenosis?
In pyloric stenosis, the muscular wall of the pyloric region hypertrophies, resulting in a severe reduction in the diameter of the pyloric canal or complete atresia
88
What is hypertrophic pyloric stenosis characterized by? (3 things)
1) polyhydramnios during fetal development
2) forceful projectile vomiting upon feeding in the newborn.
3) The thickened pylorus is detectable as the presence of a palpable OLIVE SHAPED MASS in the upper right quadrant of the abdomen, which is also detectable via radiograph or ultrasound.
89
Will the vomit caused by hypertrophic pyloric stenosis by bile stained? Why or why not?
The vomitus will be non‐bile stained because the obstruction is proximal to the where the common bile duct enters the GI tract
90
What is Duodenal atresia?
occurs when the lumen of the duodenum (midgut) fails to recannulate
91
What is duodenal atresia characterized by?
1) polyhydramnios during fetal development
2) a distended stomach and forceful projectile vomiting upon feeding in the newborn.
3) This condition is often characterized by the presence of the “double‐bubble” sign on radiograph. The double bubble refers to the appearance of the distended stomach and distended proximal duodenum separated by the pyloric valve.
NOTE: This sign may also be present in newborns with annular pancreas and some kinds of midgut malrotation, and cannot be taken as a definitive diagnosis.
92
Will the vomit caused by duodenal atresia by bile stained? Why or why not?
In this case, the vomitus will be bile‐stained because the obstruction is in the region of the GI tract where the common bile duct enters.
93
Septation of the cloaca is accomplished by what?
the growth of a mesodermal partition from the dorsal body wall called the urorectal septum. The urorectal septum grows in a dorsal to ventral direction, eventually fusing with the body surface in the perineum.
94
The urorectal septum divides the fetal cloaca into what?
a ventral side (urogenital sinus) and dorsal side (anorectal canal).
95
What does the anorectal canal form?
the hindgut (from splenic flexure to pectinate line of the anal canal)
96
What are the three regions of the urigential sinus?
a cranial region (dilated sac), an intermediate region,and a caudal region
97
Describe the cranial region of the urigenital sinus
The cranial region is connected to the umbilical stalk via the allantois and will ultimately form the urinary bladder.
98
What does the intermediate (pelvic) region of the urigential sinus form?
the entire urethra (in the female) or prostatic part, the membranous part, and most of the penile part of the urethra (in the male). It forms the lower vagina and prostate gland as well
99
What does the caudal (phallic) region of the urigential sinus form?
contributes to the external genitalia
100
As the anal canal is developing, the external opening is originally closed by the presence of what?
the anal membrane at the distal end of the hindgut (pectinate line of the anal canal)
In normal development, it will break down and its original position is indicated by the position of the pectinate line.
101
What is gut tube composed of a) above the pectinate line and b) below the pectinate line,
a) above, the gut tube that is lined by endoderm.
| b) Below the pectinate line, is perineum that is lined by ectoderm.
102
What are the five major transitions that occur at the pectinate line?
Convention: above PL is listed first, below is 2nd
1) visceral (ANS) sensory innervation to somatic sensory innervation
2) portal venous drainage to caval venous drainage
3) drain to iliac lymph nodes to drain to superficial inguinal lymph nodes
4) internal hemorrhoids (painless) to external hemorrhoids (painful)
5) endoderm derived to ectoderm derived
103
What is the most common defect of hindgut?
Imperforate anus
104
What does imperforate anus result from?
This occurs when the anal membrane fails to breakdown completely and the distal opening of the GI tract is closed
105
What is typically the cause of the anal membrane to fail to breakdown completely?
Failure of the anal membrane to breakdown is usually associated with misalignment of the urorectal septum in the dorsal direction. The urorectal septum should intersect with the midpoint of the body wall in the perineum. The distal edge of the urorectal septum forms the perineal body. Misalignment of the septum can block the opening of the anal canal to the exterior.
106
What is Hirschsprung Disease (colonic agangliosis)?
This defect results from the failure of NC cells to migrate into the hindgut region and form the parasympathetic terminal ganglia of the myenteric plexus.
107
What does Hirschsprung Disease result in?
Absence of the parasympathetic terminal ganglia will disrupt parasympathetic innervation to the distal hindgut (usually affecting sigmoid colon and rectum), resulting in loss of peristalsis, fecal retention, and distension of the gut tube (usually transverse colon) proximal to the lesion side.
108
Notes on characterization, diagnosis, and treatment of Hirschsprung disease?
It is characterized by the inability of the newborn to pass meconium during the first few days of life and can be confirmed radiologically. Notice the transverse colon is greatly distended (megacolon), proximal to the constricted, aganglionic segment of the hindgut.
As for treatment, the damaged section of the colon is usually removed surgically (colostomy). The two ends of the hindgut can usually be reconnected surgically at around 9‐10 months of age.
