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 which germ layer?
Mesoderm
Dorsal/Ventral mesentery covers…
Dorsal: Most abdominal structures; Ventral: Exists at the bottom esophagus, stomach, and upper duodenum
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? What structure divides it from the esophagus?
Foregut; Tracheoesophageal septum divides diverticulum
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
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 [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
What is the tissue above the pectinate line derived from? Tissue below?
Tissue above: hindgut; Tissue below: proctodeum (ectoderm)
The tissue above the pectinate line is composed of what type of epithelium? Tissue below?
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
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 [common/rare]
Rare
What arteries serve as an abdominal collateral between the SMA and IMA?
Marginal artery of Drummond (receives branches)
What keeps SMA away from the duodenum?
The structures that keep SMA away from the duodenum are not specified.
What is the classic presentation of a patient with SMA syndrome?
Recent, massive weight loss.
What structures does the Inferior Mesenteric artery supply?
Last 1/3 of the transverse colon, descending colon, and sigmoid colon.
What arteries serve as an abdominal collateral between the Celiac trunk and SMA?
Superior and inferior pancreaticoduodenal arteries.
Is gastric ischemia from vessel occlusion common or rare?
Rare.
What arteries serve as an abdominal collateral between the SMA and IMA?
Marginal artery of Drummond, which 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 artery (IMA) merges with middle rectal artery (iliac).
Is rectal ischemia from occlusion common or rare?
Rare.
Which intestine is most severely affected by mesenteric ischemia?
Small intestine.
What is ischemic colitis?
Ischemia of the colon.
What are four 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).
What areas of the GI tract are usually affected by non-occlusive ischemia?
Watershed areas of the colon.
What GI condition often results from non-occlusive ischemia?
Ischemic colitis.
What are two symptoms seen in mesenteric ischemia and what is the onset?
- Abdominal pain, cramping
- Usually sudden onset.
What are four common physical exam findings in mesenteric ischemia?
- 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 two 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 patients 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 four layers of the digestive tract?
- Mucosa
- Submucosa
- Muscular layer
- Serosa/adventitia.
What three 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 two components?
- Connective tissue
- Meissner’s plexus (submucosal plexus).
The muscular layer in the GI tract consists of what three components?
- Inner circular smooth muscle
- Auerbach’s plexus (between layers)
- Outer longitudinal layer.
What is abnormal in Achalasia?
Auerbach’s plexus.
The serosa layer in the GI tract consists of a layer of what?
- Surface epithelial cells (mesothelium)
- Secretes lubricating fluid.
Adventitia is found on what structures?
Retroperitoneal structures.
Adventitia is made of what and how does it compare to serosa?
- Loose connective tissue
- Compared to serosa, it is not lubricated.
What type of cells comprise the esophagus?
Non-keratinized stratified squamous epithelium.
What type of cells comprise the stomach?
Simple columnar epithelium.
What two features are unique to the gastric mucosa?
- Gastric pits
- Gastric glands (in lamina propria).
What are four types of cells found in the gastric glands?
- Parietal cells
- Chief cells
- Mucous neck cells
- G cells.
What three features are unique to the small intestinal mucosa?
- Villi
- Crypts (of Lieberkuhn)
- Microvilli.
Villi are extensions into the lumen from which layer?
Mucosa.
What do crypts (of Lieberkuhn) contain?
Goblet cells.
What are microvilli?
Microscopic extensions of the epithelial cell membrane.
What are two other names for Plicae Circulares?
- Kerckring folds
- Valvulae conniventes.
What layer(s) of the GI tract make up the Plicae Circulares?
Mucosa and submucosa.
Plicae Circulares is most abundant in which part of the GI tract?
Jejunum.
The greatest number of goblet cells is found in which part of the GI tract?
Ileum (increases in number from duodenum to ileum).
In which parts of the GI tract are goblet cells normally found?
Small and large intestine.
Where else can goblet cells be found in the setting of chronic inflammation?
In the stomach (gastritis) due to intestinal metaplasia.
Where are Brunner’s glands found?
Submucosal layer of the duodenum.
What do Brunner’s glands secrete?
- Alkaline fluid that protects intestine from acidic stomach fluid and chyme.
Brunner’s glands increase thickness in which disease?
Peptic ulcer disease.
In what layer of the GI tract are lymph cells found?
Lamina propria.
What is the distribution of lymph cells within the GI tract?
Increases from duodenum to ileum, then aggregates into Peyer’s patches.
Where in the GI tract are Peyer’s patches found and in what layer?
- Ileum
- Right beneath the muscularis mucosa in the submucosa.
What is the function of M cells?
Deliver antigens to the Peyer’s patches (acts as lymph node).
What are lacteals and what is their function?
- Lymphatic channels within villi
- Important for absorption of fats.
What does the colon produce a lot of?
Mucous.
What is the main function of the colon?
Absorbs fluid and electrolytes.
What are three distinguishing features of the colon?
- Lots of goblet cells
- Crypts without villi
- Haustra.
What are Haustra?
Pouches of the colon.
What do erosions affect compared to ulcers in the GI tract?
- Erosions: Mucosa only
- Ulcers: Submucosa and muscularis mucosa.
What does Meissner’s plexus control?
Secretion and blood flow.
What is another name for Auerbach plexus?
Myenteric nerve plexus.
What is the major role of the Auerbach plexus?
Control of GI motility.
What are slow waves in the GI tract?
Oscillating membrane potential of GI smooth muscle.
Where do slow waves in the GI tract originate?
Interstitial cells of Cajal (pacemaker cells).
How do interstitial cells of Cajal initiate action potential?
- Membrane potential ‘slowly’ rises near threshold
- When near threshold, action potentials may occur.
Slow waves set the maximum number of what per time in the GI tract?
Contractions.
What is the slow wave frequency in the stomach, duodenum, and ileum?
- Stomach: 3/min
- Duodenum: 12/min
- Ileum: 8/min.
The Ampulla of Vater is where which two ducts merge?
Common bile duct and pancreatic duct.
The Ampulla of Vater empties into which part of the GI tract?
Duodenum.
The Ampulla of Vater is the anatomical transition from the foregut to what?
Midgut (celiac trunk transition to SMA).
What structure is where bile and pancreatic enzymes enter the duodenum?
Major Duodenal Papilla.
What structure surrounds the Major Duodenal Papilla?
Sphincter of Oddi.
What is the Sphincter of Oddi and what is its function?
- Circular smooth muscle layer that surrounds the Major Duodenal Papilla
- Controls flow of bile and pancreatic enzymes into duodenum and prevents reflux.
What is Sphincter of Oddi Dysfunction?
Narrowing of Sphincter of Oddi.
Sphincter of Oddi Dysfunction can occur after what two conditions?
- Pancreatitis
- Gallstone disease.
What are four common symptoms of Sphincter of Oddi Dysfunction?
- RUQ pain
- Possible abnormal LFT, hyperbilirubinemia
- Recurrent pancreatitis.
What are two potential therapies for Sphincter of Oddi Dysfunction?
- Smooth muscle relaxant (Ca channel blocker, nitrates)
- Endoscopic sphincterotomy.
What may cause Sphincter of Oddi Spasm?
Opioids, i.e., morphine.
What is the drug of choice for pain relief in a patient with pancreatitis?
Meperidine (Demerol).
