Gastroenterology 1 Flashcards
What parts of the GI tract are derived from endoderm?
GI tract epithelium, glands, and many organs that bud off: liver, pancreas, trachea.
What 4 parts of the GI tract are derived from mesoderm?
Connective tissue/strome, muscles, peritoneum, spleen.
The foregut forms which parts of the GI tract?
Celiac trunk, mouth to ampulla of Vater (including liver, gallbladder, bile ducts, pancreas).
The midgut forms which parts of the GI tract?
SMA, ampulla of Vater to transverse colon.
The hindgut forms which parts of the GI tract?
IMA, transverse colon to rectum.
What is mesentery?
Double layer of peritoneum that suspends abdominal organs from cavity walls.
What is the mesentery derived from?
Mesoderm.
Dorsal mesentery covers…
Most abdominal structures.
Ventral mesentery covers…
Exists at the bottom of the esophagus, stomach, and upper duodenum.
What does the liver grow into?
This mesentery forms the lesser omentum and falciform ligament.
The ventral mesentery is derived from?
Septum transversum (mesenchyme tissue).
The Greater omentum hangs from the _______ and is formed from the ________.
Greater curvature of the stomach, mesogastrium.
Where is the lesser omentum and what is it formed from?
Between the liver and stomach, formed from ventral mesentery.
The ‘lung bud’ comes off from what structure?
Foregut.
What structure divides the lung bud from the esophagus?
Tracheoesophageal septum.
Esophageal atresia develops due to…
Abnormal tracheoesophageal septum development; septum deviates posteriorly.
What are 3 clinical features of esophageal atresia?
Polyhydramnios (baby cannot swallow fluid), drooling, choking, vomiting (accumulation secretion), cannot pass NG tube into stomach.
Forms of Esophageal atresia?
EA with tracheoesophageal fistula (TEF): most common, pure EA, H-Type: esophagus and trachea connected by a fistula.
What are 2 clinical findings in a patient with tracheoesophageal fistula?
Gastric distension (air in stomach on CXR), reflux → aspiration pneumonia → respiratory distress.
What is the treatment/prognosis for esophageal atresia?
Treatment: Surgical repair. Prognosis: sometimes residual dysmotility, GERD.
The midgut begins development during which week of gestation?
6th.
Describe the development of the midgut.
Abdomen is too small so intestines herniate through umbilical cord (‘physiologic herniation’ visible on ultrasound!) → midgut rotates around SMA, continues to rotate after return to abdomen by 12th week → results in cecum in right lower quadrant.
What is an omphalocele? What are 2 key features?
Persistence of normal midgut herniation through the umbilicus during development (Normally does not contain liver). Key features: Covered by peritoneum, through umbilical cord.
Liver-containing omphalocele occurs when…
Lateral embryonic folds fail.
What is the clinical presentation of Omphalocele?
Normal GI function BUT associated with other conditions i.e. congenital heart defects (50%), neural tube defects.
What 3 genetic defects are associated with Omphalocele?
Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Trisomy 13.
What is Gastroschisis? What is a key characteristic?
Extrusion of bowel through abdominal wall due to paraumbilical abdominal wall defect (usually on right side). NOT covered by peritoneum.
What is the clinical presentation of Gastroschisis?
Poor GI function, often associated with atresia, stenosis. Few associated defects → good prognosis if GI function is restored.
What is the treatment for Gastroschisis?
Surgical reduction/closure.
What are 3 possible outcomes of midgut malrotation during development?
Obstruction: Cecum can end up in mid-upper abdomen → stretches peritoneum forming Ladd bands → duodenal obstruction. Volvulus: small bowel twists around SMA → Vascular compromise → ischemia → obstruction. Left sided colon: anatomic variant.
What are the symptoms and treatment for Volvulus?
Symptoms: Vomiting, sepsis, abdominal distension. Treatment: urgent surgery.
Omphalocele vs Gastroschisis
Omphalocele: covered by peritoneum, through umbilical cord. Gastroschisis: not covered by peritoneum, extrusion of bowel.
What is the most common congenital GI abnormality?
Meckel’s Diverticulum.
By week 5, the yolk sac begins to ____ and becomes the ____
Narrow, ‘Yolk stalk,’ ‘vitelline duct,’ ‘omphalomesenteric duct.’
Vitelline duct normally disappears by which week of gestation? Persistence can lead to what?
9th week. Persistence can lead to: Meckel’s diverticulum (most common), cysts/polyps, sinus: cavity behind umbilicus, intestinal discharge from umbilicus.
What is a Meckel’s Diverticulum?
Persistent remnant of vitelline duct, diverticulum of the ileum. Involves all layers of the small bowel (mucosa, submucosa, muscular) → ‘true diverticulum.’
Meckel’s Diverticulum often contains what tissue?
‘Ectopic gastric tissue’, sometimes pancreatic tissue also.
What are the symptoms of Meckel’s Diverticulum? What are 3 possible complications?
Usually no symptoms. Complications: Gastric tissue can secrete acid → ulceration, bleeding; obstruction; diverticulitis.
What is the Meckel’s Diverticulum ‘Rule of 2s’?
2 percent of population, male-to-female ratio 2:1, within 2 feet from ileocecal valve, usually 2 inches in size.
What are 2 ways to diagnose Meckel’s diverticulum?
Technetium scan: Tracer taken up by gastric cells in diverticulum. Capsule endoscopy.
When do Meckel’s diverticulum commonly present?
In childhood.
What is the treatment for Meckel’s diverticulum?
Surgery.
Where is the most common and least common site of atresia/stenosis in the GI tract?
Most common: duodenum. Least common: colon.
What are 2 common symptoms seen in GI atresia and stenosis at birth?
Polyhydramnios, bilious vomiting.
Duodenal Atresia occurs probably due to failure of…
‘Recanalization.’
Duodenal Atresia is associated with what condition?
Down syndrome.
What sign on imaging is seen with Duodenal Atresia?
Double bubble sign (Distention of duodenum stump and stomach with tight pylorus in middle).
What is the mechanism of Jejunal-Ileal-Colonic Atresia?
Vascular disruption → ischemic necrosis of intestine → necrotic tissue is reabsorbed and leaves blind ends of bowel.
In Jejunal-Ileal-Colonic Atresia, the bowel distal to the blind end may be…
Curled → ‘Apple tree atresia.’
Newborns with Pyloric stenosis will present with [2]
‘Projectile,’ non-bilious vomiting; palpable mass (Feels like ‘olive’).
Pyloric stenosis is more common in [M/F]. 30% are [1st/2nd] born children.
Males, 1st.
Spleen arises from what tissue?
Dorsal mesodermal tissue of the stomach.
What is the arterial supply for the spleen?
Celiac trunk.
Gastrosplenic (gastrolienal) ligament carries which 2 vessels?
Short gastric arteries, left gastroepiploic vessels.
What structures are retroperitoneal?
SAD PUCKER: Suprarenal (adrenal glands), Aorta + IVC, Duodenum (2nd and 3rd segments), Pancreas (except tail), Ureters, Colon (ascending and descending), Kidneys, Esophagus, Rectum (partly).
What structures are intraperitoneal?
Stomach, appendix, liver, spleen, 1st part duodenum, jejunum, ileum, colon (transverse, sigmoid), part of rectum, tail of pancreas.
Retroperitoneal bleeding often occurs as a complication of…
Surgical procedure (but many causes).
What are the borders of the greater sac?
Entire width of abdomen, diaphragm to pelvic floor.
Where is the lesser sac located?
Behind liver, stomach, lesser omentrum.
Lesser sac is an [open/closed] space.
Closed.
What is the Epiploic foramen?
Opening between greater/lesser sac.
What are 2 other names for the Epiploic foramen?
Omental foramen, foramen of Winslow’s.
Pectinate line (or Dentate line) is part of the anal canal.
True.
What tissue above the pectinate line is derived from? Tissue below?
Tissue above: hindgut. Tissue below: proctodeum (ectoderm).
The tissue above the pectinate line is composed of what type of epithelium?
Above: columnar (similar to digestive tract). Below: stratified squamous epithelium (similar to skin).
What artery supplies the tissue above the pectinate line?
Superior rectal artery (branch of IMA).
What is the venous drainage for the tissue above the pectinate line?
Superior rectal vein → inferior mesenteric → portal system.
What is the lymphatic drainage for the tissue above the pectinate line?
Internal iliac nodes.
Veins above the pectinate line can form [internal/external] hemorrhoids?
Internal.
Tissue above the Pectinate line receives [somatic/visceral] innervation.
Visceral (no pain).
Tissue above the Pectinate line is associated with what type of cancer?
Adenocarcinoma (rare form of anal cancer).
What artery supplies the tissue below the pectinate line?
Inferior rectal artery (Branch of internal pudendal artery, off iliac).
What is the venous drainage for the tissue below the pectinate line?
Inferior rectal → internal pudendal → internal iliac → IVC.
What is the lymphatic drainage for the tissue below the pectinate line?
Superficial inguinal nodes.
Tissue below the Pectinate line receives [somatic/visceral] innervation.
Somatic (painful).
Veins below the pectinate line can produce [internal/external] hemorrhoids?
External.
Tissue below the Pectinate line is associated with what type of cancer?
Squamous cell carcinomas (more common anal CA).
The anus is formed when the ____ and ____ meet.
Hindgut and ectoderm.
Imperforate Anus is commonly associated with what 2 GU malformations?
Renal agenesis, bladder exstrophy.
Imperforate Anus commonly presents clinically with [2]
Failure to pass meconium, meconium from urethra or vagina (fistula).
What structures does the celiac trunk supply?
Foregut structures (stomach, spleen, liver, gallbladder, part of duodenum, pancreas).
At what vertebral level does the celiac trunk come off the aorta?
T12.
What are the 3 branches of the celiac trunk?
Left gastric (runs superiorly), common hepatic, splenic.
What artery(s) supply the lesser curvature?
Left and right gastric.
What artery(s) supply the greater curvature?
Left and right Gastroepiploic.
What artery(s) supplies the cardia/fundus of the stomach?
Short gastric artery (branch of splenic artery).
Gastric ulcers are more common in the [lesser/greater] curvature. Ulcers that ruptured would cause bleeding from the [artery].
Lesser, left gastric artery.
Posterior duodenal ulcers that ruptured would cause bleeding from the [artery].
Gastroduodenal artery.
Short gastric arteries are branches of the…
Splenic artery.
Why are short gastric arteries vulnerable to ischemia if splenic artery is occluded?
No dual blood supply.
Where is the Hepatoduodenal Ligament found?
On the ‘free border of lesser omentum.’
The Hepatoduodenal Ligament contains what 3 structures?
Proper hepatic artery (branch of common hepatic), cystic duct, portal vein.
What is the Pringle’s maneuver? What is it used for?
Clamping of hepatoduodenal ligament. Enables surgeons to halt hemorrhage and find the source of bleeding.
If bleeding continues after the Pringle’s maneuver, which [2] vessels are most likely the cause of bleeding?
IVC or hepatic veins.
What structures does the Superior Mesenteric artery supply?
Distal duodenum to the first 2/3 of transverse colon + appendix.
The Superior Mesenteric artery descends across the [2]
Pancreas head and duodenum.
What are arcades and vasa recta?
Arcades: Anastamoses of ileal/jejunal arteries. Vasa recta: Arteries extending from arcades.
What is SMA syndrome?
Rare cause of bowel obstruction where the distal duodenum is compressed between the aorta and SMA (Mesenteric fat normally keeps SMA away from duodenum).
Patient with SMA syndrome classically presents with…
Recent, massive weight loss.
What structures does the Inferior Mesenteric artery supply?
Last 1/3 transverse, descending, sigmoid colon.
What arteries serve as an abdominal collateral between the Celiac trunk and SMA?
Superior and inferior pancreaticoduodenal arteries (supply stomach).
Gastric ischemia from vessel occlusion is [common/rare].
Rare.
What arteries serve as an abdominal collateral between the SMA and IMA?
Marginal artery of Drummond (receives branches from middle (SMA) and left (IMA) colic arteries).
What arteries serve as an abdominal collateral between the IMA and Iliac artery?
Superior rectal (IMA) merges with middle rectal (iliac).
Rectal ischemia from occlusion is [common/rare].
Rare.
Mesenteric ischemia of the [small/large] intestine is most severe.
Small.
What is the collateral between the SMA and IMA?
Marginal artery of Drummond (receives branches from middle (SMA) and left (IMA) colic arteries)
What arteries serve as an abdominal collateral between the IMA and Iliac artery?
Superior rectal (IMA) merges with middle rectal (iliac)
Occurs in rectum
Is rectal ischemia from occlusion common or rare?
Rare
Mesenteric ischemia of the small or large intestine is most severe?
Small (often life-threatening)
What is ischemic colitis?
Ischemia of the colon
What are 4 possible causes of Mesenteric ischemia?
- Embolism: often cardiac origin (LV thrombus or LA thrombus due to AFib)
- Arterial thrombosis: usually at site of atherosclerosis
- Venous thrombosis: resistance to flow out of mesentery, one of the least common causes
- Non-occlusive ischemia: hypoperfusion/shock
If a patient presents with abdominal pain from ischemic colitis, what should you check next?
Check the heart for A-Fib
In Mesenteric ischemia, what region of the intestine is most commonly affected by embolism?
Jejunum (via SMA)
Non-occlusive ischemia usually affects what areas of the GI tract?
Watershed areas of colon
Non-occlusive ischemia often results in what GI condition?
Ischemic colitis
What are 2 symptoms seen in Mesenteric ischemia? What is the onset?
- Abdominal pain, cramping
- Usually sudden onset
What 4 physical exam findings are common in Mesenteric ischemia?
- “Pain out of proportion to exam”
- Usually mild tenderness
- No rebound tenderness or peritoneal signs
- Occult blood in stool
What labs are elevated in Mesenteric ischemia?
WBC and lactate (acidosis)
What are watershed areas?
Colon areas located between major vessels
What 2 GI structures are at the highest risk for ischemia in shock/hypoperfusion?
- Splenic Flexure
- Rectosigmoid junction
Chronic mesenteric ischemia usually occurs in what demographic?
Older patient with other vascular disease (PAD risk factors are common)
How does a patient with Chronic mesenteric ischemia present?
- Recurrent abdominal pain after eating
- Fear of eating → weight loss
- Sudden worsening may suggest acute thrombosis
What are the 4 layers of the digestive tract?
- Mucosa
- Submucosa
- Muscular layer
- Serosa/adventitia
What 3 components make up the mucosal layer in the GI tract?
- Epithelium
- Lamina propria
- Muscularis mucosa
What is the function of the lamina propria and what is found here?
- Support
- Gastric glands in the stomach
The submucosal layer in the GI tract consists of what?
- Connective tissue
- Meissner’s plexus (submucosal plexus)
The muscular layer in the GI tract consists of what?
- Inner circular smooth muscle
- Auerbach’s plexus (between layers)
- Outer longitudinal layer
What is abnormal in Achalasia?
Auerbach’s plexus
