Forms as a result of the lateral, cranial, and caudal body folds
Gut tube
Lead to the incorporation of the dorsal portion of the endodermal yolk sac into an endoderm lined tube
within the embryo (3rd to 4th week)
Lateral, cranial, and caudal body folds
The gut tube is limited at the
- ) Cranial end by>
- ) Caudal end by?
- ) Buccopharyngeal membrane
2. ) Cloacal membrane
In the 4th week, the buccopharyngeal membrane ruptures and establishes communication with the
Ectodermally lined oral cavity
In the 7th week, the cloacal membrane ruptures and establishes communication with the
Ectodermally lined anal canal
Initially, the gut tube retains its communication with the yolk sac by way of the
Vitelline duct
The vitelline duct narrows and subsequently is obliterated, thus separating the
Gut tube from yolk sac
Failure of the vitelline duct to obliterate can result in an open communication between the gut tube and the outside environment at the umbilicus. This is called a
Vitelline fistula
An open communication between the gut tube and the outside environment at the umbilicu
Vitelline Fistula
Meconium and fecal material may emerge at the umbilicus through a
Vitelline Fistula
What three things may result from incomplete closure of the vitelline duct?
- ) Vitelline cyst
- ) Vitelline sinus
- ) Meckel’s diverticulum
A cyst within a fibrous remnant of the vitelline duct
Vitelline cyst
Similar to a cyst, except it communicates with the external environment
Vitelline sinus
A diverticulum from the wall of the ileum that does not communicate with the outside environment
Meckel’s Diverticulum (ileal diverticulum)
Reportedly present in 2-3% of the population and is usually asymptomatic, although it may become inflamed and it may contain ectopic tissue
Meckel’s diverticulum
When present, Meckel’s diverticulum is usually found on the antimesenteric side of the illeum, about
2-3 ft. from the ileocecal junction
When ectopic tissue is present, it is often gastric mucosa. What does the gastric mucosa secrete that may be the cause of inflammation?
HCL
If the lateral body folds do not completely meet and fuse correctly, there may be a weakness of the anterior abdominal wall which may lead to
Gastroschisis
Provides an open communication between the abdominal cavity and the outside environment
Gastroschisis
Gastroschisis typically occurs to the
Right of the umbilicus
Failure to recanalize the gut tube results in a segment of the gut tube without a
Lumen (called atresia)
Atresia occursmost commonly in the
Duodenum
Evidence suggests that atresias in the jejunum and ileum are the result of vascular insult to a segment of the gut tube during
Development
Obstruction of the digestive tract distal to the stomach results in severe vomiting after feeding because of the
inability to
Empty the stomach
The presence or absence of bile in vomit will tell us if the obstruction is
Proximal (non-bilious) or Distal (bilious) to the entry of the common bile duct
The gut tube is divided into the
Pharynx, foregut, midgut, and hindgut
The portion of the gut tube from the buccopharyngeal membrane to the respiratory diverticulum
Pharynx
Envaginations of the pharynx include the
Pharyngeal pouches, thyroglossal duct, and respiratory diverticulum
Abnormalities in the formation of the respiratory
diverticulum may result in
Esophageal atresia, esophageal stenosis, or tracheoesophageal fistula
Prevents the fetus from swallowing amniotic fluid and results in an abnormally high volume of amniotic fluid (polyhydramnios)
Esophageal atresia
May result in thyroglossal cyst (median cervical cyst),
lingual thyroid or other ectopic thyroid tissue
Thyroglossal duct abnormalities
The foregut is supplied by the celiac trunk and vagus nerve and gives rise to the
Esophagus, stomach, and part of the duodenum
Which part of the duodenum does the foregut giverise to?
1st part and proximal portion of the 2nd part
Envaginations of the foregut give rise to
Liver, gall bladder, and the pancreas
The midgut is supplied by the
Superior mesenteric artery and vagus nerve
The midgut gives rise to what 7 things?
- ) Part of the duodenum
- ) jejunum
- ) Ileum
- ) cecum
- ) appendix
- ) ascending colon
- ) proximal 2/3 of transverse colon
What part of the duodenum does the midgut give rise to?
distal portion of 2nd part, and 3rd and 4th parts
The hindgut is supplied by the
Inferior mesenteric artery and pelvic splanchnic nerves
The hindgut gives rise to what 5 things?
- ) distal 1/3 of transverse colon
- ) descending colon
- ) sigmoid colon
- ) rectum
- ) upper part of anal canal
Gives rise only to the epithelium of the gut tube, epithelium of the gut tube derivatives and glands derived from the epithelium
Endoderm
The other layers of the gut tube organs (e.g. smooth muscle, connective tissue) are derived from
Splanchnic mesoderm
The inner layer of the lateral plate mesoderm
Splanchnic meoderm
During the formation of the gut tube by body folding, the splanchnic mesoderm is carried inward along with the endodermal gut tube and becomes the
Peritoneal covering of the gut tube and the mesenteries
Peritoneal membranes that connect the visceral peritoneum with the parietal peritoneum
Mesenteries
Serve as “bridges” to carry blood vessels, lymphatics and nerves from retroperitoneal positions to the gut tube
Mesenteries
Serves as the pathway for branches of the abdominal aorta to provide blood supply to the gut, as well as a pathway for veins, lymphatics, and nerves
Dorsal mesentery
The only vessel to traverse the ventral mesentery is the
Umbilical vein
The adult remnant of the umbilical vein is the
Ligamentum teres
The adult mesenteries derived from the ventral mesentery are the
Falciform ligament, and the lesser omentum
Contains the ligamentum teres
Falciform ligament
Contians the common bile duct, the proper hepatic artery, and the portal vein
Lesser omentum
What are two adult mesenteries derived from the dorsal mesentery?
- ) Greater omentum (includes gastrocolic ligament)
2. ) Mesentery proper (attached to jejunum and ileum)
Evaginates from the endodermal lining of the ventral wall of the gut tube in the region of the 2nd portion of the duodenum
-enters the ventral mesentery
Hepatic Diverticulum
The site of the hepatic diverticulum marks the termination of the
Foregut
What do the distal and proximal ends of the hepatic diverticulum become?
- ) Distal: liver and gall bladder
2. ) Proximal: biliary duct system
The portion of the ventral mesentery covering the liver becomes the
Visceral peritoneum of the liver
The portion of the ventral mesentery between the liver and gut tube becomes the
Lesser omentum
The portion of the ventral mesentery between the liver and ventral body wall becomes the
Falciform ligament
The part of the liver that comes into contact with the diaphragm and is not covered by peritoneum is the
Bare area of the liver
The hepatic veins exit the liver and enter the inferior vena cava through the
Bare area
The bare area is surrounded by a reflection of peritoneum from visceral peritoneum of the liver onto the parietal peritoneum on the diaphragm. This is called the
Coronary ligament
Develops from two pancreatic diverticula (buds) which evaginate from the endodermal lining of the gut tube in the region of the 2nd portion of the duodenum
Pancreas
Arises in common with the hepatic diverticulum
Ventral pancreatic bud
Initially grows into the ventral mesentery but subsequently leaves the ventral mesentery, rotates around the gut tube to enter the dorsal mesentery
Ventral pancreatic bud
The ventral pancreatic duct gives rise to which three things?
- ) Major pancreatic duct (of Wirsung)
- ) lower portion of the head of the pancreas
- ) Uncinate process
Gives rise to the minor pancreatic duct (of Santorini) and the upper portion of the head of the pancreas and the neck, body and tail of the pancreas
Dorsal pancreatic duct
Malrotation of the ventral pancreatic bud may result in
-may present symptoms of bowel obstruction
Anular pancreas
A ring of pancreatic tissue which surrounds the second portion of the duodenum
Anular pancreas
Develops in the dorsal mesentery of the stomach (dorsal megogastrium)
Spleen
Rrises from cells of the mesentery which delaminate and migrate into the plane between the layers of the mesentery
Spleen
The mesentery covering the spleen becomes the
Visceral peritoneum of the spleen
The mesentery between the spleen and the gut tube becomes the
Gastrosplenic ligament
The mesentery between the spleen and the dorsal body wall becomes the
Splenorenal ligament
Most of the splenorenal ligament fuses to become
Parietal peritoneum
The blood supply to the spleen (the splenic artery) reaches the spleen by passing within the
Splenorenal ligament
Does not develop from an envagination of the gut tube and thus is not connected to the gut by a duct
-not part of the digestive system
Spleen
Most of the gut tube retains only a dorsal mesentery. The absence of a ventral mesentery allows for
Mobility of the gut
Parts of the gut tube (most of duodenum, ascending colon, descending colon, part of rectum) fuse with the body wall by way of fusion of
Visceral peritoneum with parietal peritoneum
This results in the organ becoming secondarily retroperitoneal and the visceral peritoneum covering the organ being renamed
Parietal peritoneum
The mesentery attaching to the organ also is renamed parietal peritoneum and the vessels within the mesentery thus become
Secondarily retroperitoneal
Rotates 90 degrees around its own long axis such that the dorsal side rotates to the left and the ventral side rotates to the right
Abdominal foregut
This results in the dorsal border of the stomach becoming the left border which becomes the
Greater curvature of the stomach
The ventral border of the stomach becomes the right border which becomes the
Lesser curvature of the stomach
For this reason, the dorsal mesentery of the stomach is attached to the greater curvature and becomes the
Greater omentum
The ventral mesentery of the stomach is attached to the lesser curvature and becomes the
Lesser omentum
This rotation also creates the omental bursa (lesser sac). The communication between the lesser sac and the greater sac is the
Epiploic formamen (of Winslow)
The midgut develops an intestinal loop which herniates into the
Umbilical cord (6th week)
While in the umbilical cord and during retraction from the umbilical cord, the midgut rotates 270 degrees around an anteroposterior axis marked by the
Superior mesenteric artery
This rotation results in the jejunum being on the left and the ileum and cecum being on the
Right
It also causes the colon to assume the shape of an
Inverted U
Failure of the intestinal loop to completely retract from the umbilical cord (usually completely retracted by the 12th week), results in
Omphalocele
When the loops of bowel are found within the umbilical cord and are separated from the amniotic fluid by
the amniotic membrane covering the umbilical cord
Omphalocele
The abdominal organs are within the umbilical cord and therefore covered by the amniotic membrane and
separated from the amniotic fluid with
Omphalocele
The abdominal organs are outside of the umbilical cord, are not covered by the amniotic membrane and are in contact with amniotic fluid with
Gastroschisis
What is more common (1/4000 vs. 1/8000) omphalocele or gastroschisis?
Omphalocele
Is more often associated with chromosomal
abnormalities and other congenital defects and has an increased incidence with older maternal age (>40 years)
Omphalocele
Less frequently associated with other abnormalities and has an increased incidence with younger maternal age (<20 years)
Gastroschisis
Babies with omphalocele have a much poorer survival rate, primarily because of associated defects of the
Heart and Kidneys