Embryo IV Flashcards
Which part of the GI system is most commonly involved in pathology and developmental defects in the GI system?
Midgut
Where is the lining of the entire gut tube derived from?
Endoderm
T or F: endoderm gives rise to the smooth muscle, connective tissue and vascualture of the wall of the gut tube
False, the mesoderm gives rise to these structures
What is the blood supply and parasympathetic innervation to the foregut?
- Celiac trunk
- vagus nn.
What is the blood supply and parasympathetic innervation to the Midgut?
- Superior mesenteric a.
- vagus nn.
What is the blood supply and parasympathetic innervation to the Hindgut?
- Inferior mesenteric a.
- Pelvic Splanchnic nn.
What provides sympathetic innervation to the foregut?
Preganglionics:
- Greater Thoracic Splanchnic (T5-T9)
Postganglionics:
-Celiac and superior mesenteric ganglia
What provides sympathetic innervation to the midgut?
Preganglionics:
-Lesser Thoracic splanchnic (T10-T11)
Postganglionics:
- Celiac ganglia
- Superior mesenteric ganglia
What provides sympathetic innervation to the hindgut?
Preganglionics:
-Lumbar Splanchnic NN. (L1-L2)
Postganglionics:
-Inferior mesenteric ganglion
What are the Adult derivatives of the foregut?
Pharynx –> Duodenum (1st and 2nd)
- Pharynx (top)
- Esophagus
- Stomach
- DUODENUM (1ST AND 2ND PTS) (bottom)
Liver, Gallbladder, Biliary apparatus, Pancreas
What are the adult derivatives of the midgut?
DUODENUM (PTS 2, 3, 4) –> Proximal 2/3 of TRANSVERSE COLON
- DUODENUM (pts 2,3,4)
- Jejunum
- Ilium
- CECUM
- APPENDIX
- ASCENDING COLON
- TRANSVERSE COLON (PROX. 2/3)
What are the adult derivatives of the hindgut?
TRANSVERSE COLON (DISTAL 1/3) –> Anal canal (abv. pectinate line)
- TRANSVERSE COLON (DIST. 1/3)
- DESCENDING COLON
- SIGMOID COLON
- rectum
- Anal canal (abv. pect. ln)
When does formation of the gut tube begin and as a consequence of what?
4th week
Results from body foldings laterally and from head to tail
T or F: by the 4th week of development the endodermal layer is lining the trilaminar disc as well as the upper part of the yolk sac.
True
Describe how the linea alba is formed?
- Lateral folds form on both sides and include all 3 germ layers
- In about a week these move ventrally and fuse at the midline
- This fusion = linea alba
What part of the yolk sac is the primative gut tube derived from and how does this happen?
Derived from the upper endoderm lined part
- Part of yolk sac is formed by lateral body foldings
- Ventral folding causes endoderm lined part to get pinched off and internalized
- Vitillline duct is left as the only narrow communication between primative gut tube and yolk sac
What embryonic structure is the forerunner to the pleural, pericardial, and peritoneal cavities?
Embryonic coelum
What kind of folding results in the formation of foregut, hindgut, and midgut?
- head to tail body folding
- foregut = anterior
- hindgut = posterior
- midgut = in between
When does the vitelline duct close?
w8 -9
T or F: the foregut undergoes a 270º clockwise rotation in development
False, it undergoes a 90º clockwise rotation
-Note: this is relative to the viewer looking at the fetus not the fetus
Describe what happens during midgut rotation. What is the axis of this rotation?
- 270º counterclockwise rotation
- axis = SMA
What is herniation and why does it occur?
- midgut is forced out because the liver takes up so much space
Note: elongation and herniation occur in weeks 6-10
The hindgut does not require rotation but rather ____________.
Septation
What double layered reflection of visceral peritoneum suspends the primitive gut tube?
mesentery (dorsal and ventral for foregut, rest is dorsal only)
-Note: This serves as a conduit for the passage of neruovascular structures to the abdominal viscera
What part of the primitive gut tube is attached by both dorsal and ventral mesenteries?
Foregut
What 3 organs have both intraperitoneal and retroperioneal portions?
- Duodenum (1st pt. intraperitoneal)
- Colon (transverse and sigmoid intraperitoneal)
- Pancreas (tail intraperitoneal)
Which mesentery is the liver and biliary system formed in?
- Ventral, thus all adult peritoneal attachments to the liver develope from the ventral embryonic mesentery
What are the components of the ventral mesentery?
- Faciform ligament contains:
a. ligamentum teres - Lesser omentum consisting of:
a. hepatogastric ligament
b. hepatoduodenal ligament
What ligament of the lesser omentum conveys the structures in the portal triad (porper hepatic a., hepatic portal v., common bile duct)
Hepatoduodenal ligament
What is the only foregut viscera that developes from mesoderm?
Spleen
In what mesentery does the spleen develope?
Dorsal embryonic mesentery
T or F: the gastrosplenic ligament is between the spleen and lesser curvature of the stomach
False, the gastrosplenic ligament is between the spleen and greater curvature of the stomach
Note: the lesser curvature is attached to structures derived from the ventral embryonic mesentery
Between the Splenorenal and gastrorenal ligaments, which is the most important and why?
- Splenorenal ligament
- Contains Splenic vessels and tail of the pancreas
T or F: the splenorenal ligament is one of 3 ligaments that comprise the greater omentum.
False, the gastrosplenic ligament is one of the 3 ligaments comprising the greater omentum (gastrocolic and gastrophrenic are the others)
Describe the placement of the liver and spleen prior to foregut rotation.
Spleen at 12:00
Liver at 6:00
-Stomach acting as the axis of rotation
Describe the placment of the liver and spleen following foregut rotation.
Spleen from 12:00 to 3:00 (into left upper quadrant)
Liver from 6:00 to 9:00 (into right upper quadrant)
What effect does foregut rotation have on the pancreas?
- the pancreas is pushed up against the body wall and becomes retroperitoneal
- tail of the pancreas remains intraperitoneal in the splenorenal ligament
T or F: the lesser sac/omental bursa forms as a result of foregut rotation.
True
What opening is just posterior to the hepatoduodenal ligament?
epiloic foramen
Between what two structures does the visceral peritoneum fold to form a 4 layers?
Greater Curvature of the stomach and the transverse colon
-THIS IS THE GREATER OMENTUM
T or F: all adult mesenteries are derived from dorsal embryonic mesentery.
False, the falciform ligmanent and hepatoduodenal ligaments are not, but the rest are.
What mesentery extends between the transverse colon and pancreas?
Transverse mesocolon
What 4 places does the parietal peritoneum reflect off of the body wall to form mesenteries?
- Falicform ligament (diaphragm onto liver)
- Transverse mesocolon (pancreas to transverse colon)
- Mesentery Proper (dorsal body wall to small intestine)
- Sigmoid mesocolon (dorsal body wall to sigmoid colon)
T or F: the stomach is rotated 90º around both its longitudinal and transverse axes?
T
Explain the embryonic and adult orientations of the liver.
- lesser curvature that faces superiorlyin adult was originally anterior (explains lesser omentum being a ventral mesentery derivative)
- Greater curvature directed down in an adult was originally oriented posterior (explains greater omentum being a dorsal mesentery derivative)
What is the anterior boundary of the omental bursa?
Stomach and lesser omentum
What is the posterior boundary of the omental bursa?
aorta, pancreas, and left kidney
What 3 systems develop as buds from the endodermal lining of the foregut?
- Lungs and lower respiratory tract (bud in esophageal region)
- liver and biliary tract (bud in duodenal region)
- pancreas (bud in duodenal region)
How does respiratory tract development begin during the 4th week of development?
- Begins as a single respiratory diverticulum off of the esophagus that bifurcates to R and L respiratory trees (12-14 divsions proceed this one)
Why are weeks 25-28 critical to development of the respiratory system?
Type I and II pneumocytes develope to allow for gas exchange
What closes off communication between the foregut and trachea?
trachoesophageal septum (from mesoderm)
Malformation of what embryonic structure leads to the formation of a tracheoesophageal fistula?
-Trachoesophageal septum fails to form (MESODERMAL ISSUE)
Result:
- Esophageal atresia (eso. ends in blind pouch) milk comes back out of the baby’s mouth on first feeding (not vomiting)
- Tracheoesophageal fistula occurs leaving to trachea open to the GI tract
What may be a symptom of a tracheoesophageal fistula in fetal life?
polyhydramnios because the baby can’t swallow
T or F: the pancreas developes from the mesodermal part of the duodenal region in weeks 5-6
False, it develops from the endodermal lining
What parts of the pancreas do the ventral and dorsal pancreatic buds form after coming together?
Ventral Pancreatic Bud:
- head and uncinate process of the pancreas
Dorsal Pancreatic Bud:
-neck body, and tail of pancreas
T or F: both ventral and dorsal pancreatic buds contribute to the formation of the pancreatic duct
True
Describe the condition of the pancreas that can lead to polyhydamnios and projectile vomiting (bile stained) in a newborn.
annular pancreas
- VENTRAL pancreatic bud splits and part rotates ventral to the duodenum and the other parts goes dorsal causing atresia
T or F: liver and biliary tract develope from an endodermal bud off of the duodenal region
True
5 consequences of foregut rotation.
- Positional Change of the Stomach
- Formation of omental bursa
- Position of liver, spleen, and pancreas
- postnatal components of dorsal and ventral embryonic mesenteries
- Formation of C-shaped duodenum
When does most of the rotation and herniation of the midgut take place?
Week 6:
90º rotation counterclockwise around the axis of the SMA
Week 10:
180º rotation as midgut is retracted back into the abdominal cavity
Describe the original U-shaped midgut and the structures that it gives rise to.
Cranial Loop - form from the proximal part of the midgut (duodenum, jejunum, and proximal ileum) [undergoes most of the growth and coiling]
Caudal Loop - forms from the distal ileum through the splenic flexure of the transverse colon
Describe the events as the midgut returns to the abdominal cavity in the 10th week.
- Jejunum (cranial limb) is the first to return
it moves to the upper left - Ileum goes to upper right side
- Cecum enters last and goes upper right then descends to lower right
**This final event explains the positioning of the ascending, transverse, and descending colon
What are the two main types of midgut defects?
Omphalocele and Gastroschisis
What is omphalocele?
Midgut defect
- Herniated gut tube doesn’t retract because it gets stuck in the umbilical stalk
- Newborn has intestines hanging out THOUGH THE UMBILICAL RING
- Intestines are covered with amnion
- *Ofter accompanied by other CV and NS defects and is life threatening
What is Gastoschisis?
Midgut Defect
- Caused by weakness left in abdominal wall after the umbilical vein obliterates
- intestine protrudes through the abdominal wall TO THE SIDE OF THE UMBILICAL RING
- NOT COVERED BY AMNION
T or F: both omphalocele and gastroschisis result in elevated levels of AFP.
True
What is Volvolus?
Abnormal twisting of the gut tube (malrotation)
- does not result in obstruction
What are the two communications between the developing GI tract and the umbilicus?
- Vitelline Duct - connects midgut and umbilicus
2. Allantois - connects cloaca (future bladder) with the umbilicus
Between the vitelline duct and allantois, which closes first and when does this happen?
- vitelline duct closes first and the allantois closes about a week later
- this happens around weeks 8-10
What is the urachus (aka median umbilical ligament)?
adult remnant of the allantois
What are two of the more common newborn defects related to the Vitelline Duct?
- Meckel’s Diverticulum (most common defect of the midgut)
- Vitelline Fistula
Describe Meckel’s Diverticulum.
Vitelline Duct issue:
- Distal portion closes
- Proximal portion stays open
Result:
- Blind pouch in the ileal region (can become infected or get ulcerated)
RULE OF 2’s:
2% of population
~ 2in long
~ 2 ft from ileocecal junction
Describe Vitelline Fistula.
Vitelline Duct issue:
- entire vitelline duct remains patent at birth
Characteristics:
- direct communication between lumen of the midgut and the rest of the body
- oozing of meconium from the umbilical stup at birth
What is a vitelline cyst?
Isolated regions anywhere along the length of the vitelline duct that remains patent
What are 3 urachal Abnormalities and what fetal structure malforms to cause these?
Allantois issues
- Urachal Fistula
- Vesicourachal diverticulum
- urachal cyst
Describe Urachal Fistula.
Allantois remains patent at birth
- open communication btwn bladder and exterior of the body at the umbilicus
Characteristic:
- oozing of urine from the umbilical stump of the newborn
Describe urachal cysts.
Isolated patencies along the urachus
- no leakage of urine
- forms a second urine containing pouch
Describe urachal diverticuli.
May develope later in life where uracus scarred down but didn’t seal tightly
- second outpouching formed in the bladder
- Prostate disease and other conditions that raise urinary bladder pressure may cause the disease to manifest
Describe pyloris stenosis
Hypertrophy of muscular wall of pyloric region
- Associated with polyhydramnios in pregnancy
- Projectile vomiting after newborn is fed
- Vomit is NOT bile stained (obstruction proximal to bile duct entry)
- Thickened pylorus is detected as a palpable olive shaped mass
What other diseases have symptoms similary to pyloris stenosis, and how can the two be differentiated?
- annular pancreas and duodenal atresia are similar to pyloric stenosis except annular pancreas and duodenal atresia lead to BILE STAINED projectile vomiting, while pyloris stenosis does not.
- annular pancreas and duodenal atresia would probably have to be differentiated via imaging
Describe Doudenal Atresia.
- Lumen of duodenum fails to recannulate
Signs
- Polyhydramnios
- distended stomach
- projectile vomiting
- double bubble on radiograph
T or F: like the midgut the hindgut is also formed by rotation.
False, it is formed by septation
What layer of the trilaminar disc creates the septum of the hindgut and what is the septum called?
- Mesoderm gives rise to the urorectal septum
What regions is the cloaca separated into as a result of the urorectal septum?
- Urogenital Sinus (ventally)
- anorectal canal (dorsally)
What are the 3 regions of the urogenital sinus?
Cranial region (dilated sac) --> Urinary Bladder Intermediate region --> Urethra (lower vagina and prostate) caudal region --> external genitalia
What is the pectinate line an what does it represent.
- anal membrane exists here until is breaks down
- above pectinate line = endoderm
- below pectinate line = ectoderm
What vessels, nerves, and tissue make up the rectum above the pectinate line?
- Visceral ANS sensory innervation
- Portal Venous Drainage
- Drain to iliac lymph nodes
- Internal Hemorrhoids (painless)
- Endoderm
What vessels, nerves, and tissue make up the rectum below the pectinate line?
- somatic sensory innervation
- caval venous drainage
- drain to superficial inguinal nodes
- external hemorrhoids (painful)
- ectoderm
What is the most common defect of the hindgut and what are its characteristics?
Imperforate anus
- anal membrane fails to completely breakdown
caused by:
-misalignment of urorectal septum in dorsal direction
What newborn defect of the hindgut results from failure of neural crest cells to migrate appropriately?
Hirschsprung Disease (colonic angangliosis)
Describe Hirschsprung disease.
- NC do not migrate to hingut to form the parasympathetic terminal ganglia of myenteric plexus
Result of malformation:
- loss of peristalisis
- fecal retention
- distention of gut tube (usually transverse colon)
Signs:
newborn doesn’t pass meconium during 1st few days of life
