Flashcards in Digestive System - HY Deck (113):
How is the primitive gut tube formed?
From the incorporation of the DORSAL part of the yolk sac into the embryo due to craniocaudal folding + lateral folding of the embryo.
The primitive gut extends from the ...?
Oropharyngeal membrane to the cloacal membrane and is divided into the:
Early in the development, the epithelial lining of the gut tube ...?
Proliferates rapidly and OBLITERATES the lumen. (Later --> Recanalization)
6. Upper duodenum.
1. Lower duodenum.
6. Ascending colon.
7. Proximal 2/3 of the transverse colon.
1. Distal 1/3 of the transverse colon.
2. Descending colon.
3. Sigmoid colon.
5. Upper anal canal.
Foregut derivatives are supplied by the ...?
Formation of the esophagus:
The foregut is divided into the esophagus dorsally and the trachea ventrally by the tracheoesophageal folds --> Fuse to form the tracheoesophageal septum.
Clinical considerations regarding the esophagus:
1. Esophageal atresia.
2. Esophageal stenosis.
Esophageal atresia develops when the ...?
Tracheoesophageal septum deviates too far dorsally --> Esophagus ends as a closed tube.
About 33% of patients with esophageal atresia have other congenital defects associated with ...?
VATER --> Vertebral defects, anal atresia, tracheoesophageal fistula, and renal defects.
VACTERL --> Like VATER + Cardiovascular defects and UPPER LIMB defects.
Esophageal atresia is associated clinically with ...?
2. Tracheoesophageal fistula.
Esophageal stenosis occurs when ...?
The lumen is narrowed and usually involves the MIDESOPHAGUS.
Esophageal stenosis may be caused by ...?
1. Submucosal/muscularis externa hypertrophy.
2. Remnants of the tracheal cartilaginous ring within the wall of the esophagus.
3. Membranous diaphragm obstructing the lumen probably due to incomplete RECANALIZATION.
Formation of the stomach:
A fusiform dilatation forms in the foregut in week 4 --> Gives rise to the PRIMITIVE STOMACH.
Fate of the primitive stomach:
Rotates 90 degrees clockwise around its longitudinal axis.
As a result of this CLOCKWISE rotation of the primitive stomach:
1. The dorsal mesentery is carried to the left and eventually forms the GREATER OMENTUM.
2. The LEFT vagus nerve --> Innervates the VENTRAL surface of the stomach.
3. The RIGHT vagus nerve --> Innervates the DORSAL surface of the stomach.
Formation of the stomach - Clinical consideration:
Hypertrophic pyloric stenosis.
Hypertrophic pyloric stenosis occurs when?
When the muscularis EXTERNA in the pyloric region HYPERTROPHIES, causing a narrow pyloric lumen that obstructs food passage.
Which antibiotic has been associated with hypertrophic pyloric stenosis?
1st step in the formation of the liver:
The ENDODERMAL lining of the foregut forms an outgrowth (=Hepatic DIVERTICULUM) into the surrounding MESODERM of the septum transversum.
2nd step in the formation of the liver:
Cords of hepatoblasts (called hepatic cords) from the hepatic diverticulum grow into the MESODERM of the septum transversum.
3rd step in the formation of the liver:
The hepatic cords arrange themselves around the VITELLINE VEINS + UMBILICAL VEINS --> Which course through the septum transversum and form the HEPATIC SINUSOIDS.
4th step in the formation of the liver?
The liver bulges into the abdominal cavity, thereby stretching the septum transversum to form the VENTRAL MESENTERY = Falciform ligament + Lesser omentum.
The falciform ligament contains ...?
The LEFT umbilical vein, which regresses after birth to form the ligamentum teres.
Formation of the liver - Clinical considerations:
Congenital malformations of the liver are rare.
Formation of the gallbladder and bile ducts:
1. The connection between the hepatic diverticulum and the foregut narrows to form the BILE DUCT.
2. An outgrowth from the bile duct gives rise to the GALLBLADDER RUDIMENT + Cystic duct.
5 clinical considerations regarding the formation of the gallbladder and bile ducts:
1. Intrahepatic gallbladder.
2. Floating gallbladder.
3. Developmental anomalies of the cystic duct anatomy.
4. Developmental anomalies of the gallbladder anatomy.
5. Biliary atresia.
Intrahepatic gallbladder occurs when ...?
The gallbladder rudiment advances beyond the hepatic diverticulum and becomes buried within the substance of the liver.
Floating gallbladder occurs when ...?
The gallbladder rudiment lags behind the hepatic diverticulum and thereby becomes suspended from the liver by a mesentery.
Floating gallbladder is at risk for ...?
Developmental anomalies of the cystic duct anatomy are ...?
Developmental anomalies of the gallbladder are fairly common:
1. Two gallbladders.
2. Bilobed gallbladder.
3. Diverticula of the gallbladder.
4. Septated gallbladders.
Biliary atresia is defined as the ...?
Obliteration of the extrahepatic and/or intrahepatic ducts --> Replaced by fibrotic tissue due to acute/chronic inflammation.
Biliary atresia - Clinical findings:
1. Progressive neonatal jaundice with onset soon after birth.
2. White, clay-colored stool.
3. Dark-colored urine.
Biliary atresia - Average survival time:
Biliary atresia mortality:
100% (Only liver transplantation is cure).
What is the origin of the ventral and dorsal pancreatic buds?
They are direct outgrowths of foregut ENDODERM.
What happens WITHIN BOTH pancreatic buds?
Endodermal tubules surrounded by MESODERM branch repeatedly to form ACINAR cells + Ducts (i.e. exocrine pancreas).
How are the islet cells inside the pancreas formed?
Isolated clumps of ENDODERMAL cells bud from the tubules + accumulate WITHIN the mesoderm to form islet cells (ie endocrine pancreas).
How does the ventral bud fuse with the dorsal bud of the pancreas?
Because of the 90 clockwise rotation of the duodenum, the ventral bud rotates DORSALLY and fuses with the DORSAL bud to form the definitive adult pancreas.
The ventral bud of the pancreas forms the ...?
1. Uncinate process.
2. Portion of the head of the pancreas.
The dorsal bud of the pancreas forms the ...?
1. Remaining portion of the head.
3. And tail of the pancreas.
The main pancreatic duct is formed by the anastomosis of ...?
The distal 2/3 of the dorsal pancreatic duct (the proximal 1/3 regresses) + the ENTIRE ventral pancreatic duct (incidence 48%).
How does accessory pancreatic duct develop?
When the proximal 1/3 of the DORSAL pancreatic duct persists + opens into the duodenum through the minor papillae (33% incidence).
Incidence of pancreas divisum?
Pancreas divisum occurs when ...?
The distal 2/3 of the DORSAL pancreatic duct + The ENTIRE VENTRAL pancreatic duct fail to anastomose.
+ The proximal 1/3 of the DORSAL pancreatic duct PERSISTS.
The dorsal pancreatic duct drains a portion of ...?
The ventral pancreatic duct drains the ...?
Uncinate process + A portion of the head by opening into the duodenum through the major papillae.
Patients with pancreas divisum are prone to ...?
Pancreatitis --> Especially if the opening of the DORSAL pancreatic duct at the minor papillae is small.
Annular pancreas is caused when ...?
The ventral pancreatic bud fuses with the dorsal bud BOTH dorsally + ventrally, thereby forming a ring of pancreatic tissue around the duodenum --> SEVERE duodenal obstruction.
Annular pancreas - Radiograph?
The upper duodenum develops from the ...?
Caudal portion of the foregut.
The LOWER duodenum develops from ...?
The cranial-most part of the midgut.
Where is the junction of the UPPER + LOWER duodenum?
Just distal to the opening of the common bile duct.
Formation from jejunum to proximal 2/3 of transverse colon - 1st step:
The midgut forms a U-shaped loop (midgut loop) that herniates through the primitive umbilical ring into the extraembryonic coelom (ie physiological umbilical herniation) beginning at week 6.
The midgut loop consists of ...?
A cranial limb and a caudal limb.
The cranial limb of the midgut loop forms the ...?
Jejunum + Upper Ileum. (The caudal limb forms the rest)
The midgut loop rotates ...?
A total of 270 degrees COUNTERCLOCKWISE around the SMA as it returns to the abdominal cavity --> Thus reducing the physiological herniation, around week 11.
Omphalocele - When does it occur?
When abdominal contents herniate through the umbilical ring + persist outside the body covered variably by a translucent peritoneal membrane sac (a light-gray, shiny sac) protruding from the base of the umbilical cord.
Large omphaloceles may contain ...?
Small omphaloceles contain only ...?
Omphaloceles are usually associated with other congenital anomalies:
1. Trisomy 13.
2. Trisomy 18.
3. Beckwith-Wiedemann syndrome.
Gastroschisis occurs when there is ...?
A defect in the ventral abdominal wall usually to the RIGHT of the umbilical ring through which there is a massive evisceration of intestines (other organs may also be involved).
Gastroschisis - The intestines are ...?
NOT covered by peritoneal membrane, are directly exposed to amniotic fluid, and are thickened + covered with adhesions.
Meckel diverticulum occurs when ...?
A remnant of the vitelline duct PERSISTS --> Forms an outpouching located on the ANTIMESENTERIC BORDER of the ileum.
Meckel diverticulum may have ...?
Heterotopic gastric mucosa --> Ulcer, GI bleeding.
Non rotation of the midgut loop occurs when ...?
The midgut loop rotates only 90 degrees counterclockwise.
What happens in non rotation of the midgut loop?
1. The small intestine is positioned entirely on the RIGHT SIDE.
2. The large intestine is positioned entirely on the LEFT SIDE.
3. The cecum located either in the LEFT UPPER QUADRANT or in the LEFT ILIAC fossa.
Malrotation of the midgut occurs when ...?
The midgut loop undergoes only partial COUNTERCLOCKWISE rotation.
Malrotation of the midgut loop results in ...?
The cecum + appendix lying in a subpyloric or subhepatic location and the small intestine suspended by only a vascular pedicle (ie not a broad mesentery).
A major complication of malrotation is ...?
Volvulus - Twisting of the small intestine around the vascular pedicle --> Which may cause necrosis due to compromised blood supply.
What should be considered when diagnosing appendicitis regarding the malrotation of the midgut loop.
The ABNORMAL position of the appendicitis.
When malrotation is surgically corrected ...?
The appendix is REMOVED to prevent delayed or missed diagnosis of appendicitis given the atypical abdominal pain location at presentation.
Reversed rotation of the midgut occurs when ...?
The midgut loop rotates CLOCKWISE instead of counterclockwise --> Causing the large intestine to enter the abdominal cavity first.
Reversed rotation of the midgut loop results in ...?
Large intestine being anatomically located POSTERIOR to the duodenum and SMA.
Intestinal atresia + Stenosis - Causes:
1. Failed recanalization.
2. AND/OR and ischemic intrauterine event ("vascular accident").
Clinical findings of proximal atresias include:
2. Bilious vomiting early after birth.
Clinical findings of distal atresias include:
1. Normal amniotic fluid levels.
2. Abdominal distention.
3. Later vomiting.
4. Failure to pass meconium.
Duplication of the intestines occurs when ...?
A segment of the intestines is duplicated as a result of abnormal recanalization (MC near the ileocecal valve).
Duplication of the intestines is found on the ... border?
Duplication of the intestines - Clinical findings:
1. Abdominal mass.
2. Bouts of abdominal pain.
4. Chronic rectal bleeding.
Intussusception occurs when ...?
A segment of bowel invaginates or telescopes into an adjacent bowel segment --> Leading to obstruction or ischemia.
Intestinal obstruction in children
Intussusception most commonly involves ...?
The ileum and colon (ie ileocolic).
Intussusception - Clinical findings include:
1. Acute onset of intermittent abdominal pain.
3. Bloody stools.
SMA syndrome occurs when ...?
The 3rd portion of the duodenum is compressed DUE TO DECREASED ANGLE (as low as 6 degrees) between the SMA and the AORTA.
SMA syndrome - Etiology:
Loss of the intervening mesenteric fat pad due to a significant weight loss -->
1. Bariatric surgery.
4. Spinal cord injury.
5. Corrective surgery for scoliosis.
The cranial end of the hindgut develops into ...?
1. Distal 1/3 of the transverse colon.
2. Descending colon.
3. Sigmoid colon.
The terminal end of the hindgut is an ...?
ENDODERM-LINED pouch called CLOACA, which contacts the surface ECTODERM of the proctodeum to form the CLOACAL MEMBRANE.
Formation of rectum and upper anal canal - The cloaca is partitioned by the ...?
1. Urorectal septum into the rectum and upper anal canal.
2. And the urogenital sinus.
The cloacal membrane is partitioned by the ...?
Urorectal septum into anal membrane + urogenital membrane.
The urorectal septum fuses with the ...?
Cloacal membrane at the future site of the gross anatomic PERINEAL BODY.
Formation of the rectum and upper anal canal - Clinical considerations:
1. Hirschsprung disease (colonic agangliosis).
2. Rectovesical, rectourethral, and rectovaginal fistulas.
Colonic agangliosis is caused by the ...?
ARREST of the caudal migration of neural crest cells.
Colonic agangliosis - Although the ganglion cells are absent ...?
There is proliferation of hypertrophied NERVE FIBER BUNDLES.
Colonic agangliosis - Most characteristic functional finding?
The failure of the anal sphincter to relax following rectal distention (ie abnormal rectoanal reflex).
Colonic agangliosis - Clinical findings include:
1. Distended abdomen.
2. Inability to pass meconium.
3. Gushing of fecal material upon a rectal digital exam.
4. Loss of peristalsis in the colon segment distal to the normal innervated colon.
Rectovesical, rectourethral, and rectovaginal fistulas are due to ...?
ABNORMAL formation of the urorectal septum.
A rectourethral fistula that generally occurs in males is associated with the prostatic urethra and is therefore sometimes called ...?
A rectoprostatic fistula.
Formation of the anal canal - The upper anal canal develops from ...?
The lower anal canal develop from the ...?
What is the proctodeum?
An invagination of surface ectoderm caused by a proliferation of mesoderm surrounding the anal membrane.
The junction between the upper and the lower anal canals is indicated by the ...?
PECTINATE line --> Also marks the site of former ANAL MEMBRANE.
In the adult, the pectinate line is located ...?
At the lower border of the ANAL COLUMNS.
4 Clinical considerations about the formation of the anal canal?
1. Imperforate anus.
2. Anal agenesis.
3. Anorectal agenesis.
4. Rectal atresia.
Imperforate anus occurs when ...?
The anal membrane fails to perforate; a layer of tissue separates the anal canal from the exterior.
Anal agenesis occurs when ...?
The anal canal ends as a BLIND SAC below the puborectalis muscle due to abnormal formation of the urorectal septum.
Anal agenesis is usually associated with?
Anorectal agenesis occurs when ...?
The rectum ends as a BLIND SAC ABOVE the puborectalis muscle due to abnormal formation of the urorectal septum.
What is the MC type of anorectal malformation?
Anorectal agenesis is associated with?