GI Flashcards
Patient with ulcerative colitis experiences abdominal pain and distention, fever, diarrhea, signs of shock - what are you worried about?
Toxic megacolon
What do we use to diagnose toxic megacolon?
Plain abdominal X-ray
Barium enema and colonoscopy are contraindicated because they may cause rupture
Is toxic megacolon seen more often in ulcerative colitis or Crohn’s?
Ulcerative colitis
Spared rectum - ulcerative colitis or Crohn’s?
Crohn’s
Transmural inflammation - ulcerative colitis or Crohn’s?
Crohn’s
Continuous mucosal damage - ulcerative colitis or Crohn’s?
Ulcerative colitis
What happens if the angle between the SMA and aorta becomes more acute?
Superior mesenteric artery syndrome
At what level does the SMA leave the aorta?
L1
What part of the duodenum becomes entrapped in superior mesenteric artery syndrome?
Transverse portion of the duodenum
Two immunoglobulin monomers + J chain + secretory component = ?
Secretory form of IgA
Where do we find secretory form of IgA
Tears, saliva, mucus, colostrum
What is colostrum?
First breast milk fed to an infant
What acid-base disturbance can Mallory-Weiss lead to?
Metabolic alkalosis from loss of H+ in the repeated episodes of vomiting
Abdominal X-ray shows air in the gallbladder and biliary tree - what does this make you suspicious of?
Gallstone ileus - a large gallstone causes the formation of a cholecystenteric fistula between gallbladder and adjoining gut tissue; the gallstone is able to pass through the fistula and the fistula then allows gas from the small bowel to enter the gallbladder
What happens to the gallstone in gallstone ileus?
Typically goes through the fistula but then gets stuck at the ileocecal valve
Imperforate anus (abnormal development of anorectal structures) is most commonly associated with what other developmental defects?
Urogenital tract anomalies
Contrast the different mediators of the body’s immune defense against localized vs. hematogenous infection by candida.
Localized - T cells vs. hematogenous - neutrophils
Esophageal biopsy showing moderately differentiated tumor cells with keratin nests and pearls - squamous cell or adenocarcinoma of the esophagus?
Squamous cell
What are 3 major risk factors for squamous cell carcinoma?
EtOH, smoking, consumption of foods with nitrosamines
Describe what happens in base excision repair.
- Glycosylases remove the defective base
- Endonuclease and then lyase cleave and remove the corresponding sugar-phosphate
- DNA polymerase replaces the missing nucleotide
- Ligase reconnects the DNA strand
What do you see on histology of squamous cell carcinoma of esophagus?
Keratin pearls
Presentation: colicky abdominal pain, constipation, irritability, headaches, works at a battery manufacturing plant - diagnosis?
Lead poisoning
Essential fructosuria is a benign disorder resulting from a defect/deficiency in what enzyme?
Fructokinase
What is the difference between metaplasia and ectopy?
Ectopy is the result of congenital malformation vs. metaplasia occurs during adult life
What is ectopy?
Microscopically and functionally normal cells/tissues found in an abnormal location due to embryonal maldevelopment
What’s the difference between gastric erosion vs. ulcer?
Erosion - mucosal defects that do not fully extend through the muscularis mucosa (i.e. limited to the mucosa layer)
Ulcer - mucosal defects that penetrate through the mucosal layer and extend into the submucosa
When an ulcer penetrates the posterior duodenal wall, it is likely to erode into what artery?
Gastroduodenal
What does it mean that the lac operon in E. coli (codes for proteins for lactose metabolism) is polycistronic?
One mRNA codes for several proteins (in this case, it encodes genes z, y, and z which are beta-galactosidase, permease, and beta-galactoside transacetylase respectively)
What should you think of if a hospitalized patient on broad spectrum antibiotics suddenly develops white/yellow membrane like plaques on the colonic mucosa accompanied with loose stools, low grade fever, and leukocytosis?
C. difficil overgrowth
Gastroenteritis caused by oxidase positive, gram negative, comma shaped rod that can survive on alkaline media - organism?
Vibrio cholerae
What is the mechanism of action of Ribavirin?
Thought to be multifactorial but ultimately leads to interference with the duplication of viral genetic material:
- Lethal hypermutation (since it is a nucleoside analog)
- Inhibition of RNA polymerase
- Inhibition of inosine monophosphate dehydrogenase (depletes GTP)
- Enhancing Th1 response
- Inhibition of RNA guanylyltransferase and methyltransferase resulting in defective 5’ cap
Which cells does Shigella invade?
M cells in the Peyer’s patches
What are the 3 main causes of HIV-associated esophagitis?
Candida, CMV, HSV-1
What would you see on stool microscopy with vibrio?
Just mucus and epithelium because vibrio does not invade the mucosa or cause enterocyte death
What would you likely need to supplement in a patient who has a gastrojejunostomy?
Iron because you have now bypassed the duodenum and proximal jejunum where iron is typically absorbed
What part of the immunoglobulin do macrophages and neutrophils bind?
Fc portion
What down regulates gastric acid secretion after a meal?
Intestinal influences (colon and ileum release peptide YY on ECL and inhibit histamine release which would stimulate gastrin)
Presentation: pruritus, rash, flushing, abdominal cramps, lots of mast cells on small intestine biopsy - diagnosis?
Mastocytosis - gastric hypersecretion from mast cell proliferation which leads to lots of histamine release
What is the first event in the pathogenesis of acute appendicitis?
Obstruction of the lumen
Is Meckel’s diverticulum a true or false diverticulum?
True
What GI side effect can opioids have?
Contraction of smooth muscles in the Sphincter of Oddi leading to increased pressures in the bile duct and gall bladder
How does secretory IgA defend against bacteria?
Binds to pili and other outer membrane proteins that mediate bacterial adherence and penetration through the mucosa
What mutation is required for the first step in the emergence of small adenomatous polyps from normal colonic mucosa?
APC
False diverticula are also called what?
Pulsion diverticula - created by herniation through weak spots in the colonic muscular layer
Upon lactose challenge, what are the significant findings in lactase-deficient individuals?
- Increased stool osmotic gap
- Increased breath hydrogen content
- Decreased stool pH
What is polyethylene glycol?
Osmotic laxative
What molecule is involved in mediating the accumulation of pus?
IL-8 because it induces chemotaxis and phagocytosis in neutrophils
What is a pancreatic pseudocyst?
Common complication of acute pancreatitis in which there is a collection of fluid rich in enzymes and inflammatory debris with walls consisting of granulation tissue and fibrosis
Dietary lipids are primarily absorbed where?
Jejunum
What hormone stimulates the release of bicarbonate rich secretions from the pancreas?
Secretin
Where is secretin produced?
Duodenum
Hyperammonemia in hepatic encephalopathy results in depletion of what 2 things?
Alpha-ketoglutarate and glutamate
Where is the esophagus located on CT?
Between the trachea and the vertebral bodies in the superior thorax
Retroperitoneal hematoma in a stable patient is likely to occur due to injury to what organ?
Pancreas
What organisms are most common in intraabdominal infections?
Typically polymicrobial but most commonly contain Bacteroides and E. coli
What is the most effective treatment for patients with peptic ulcer disease?
Get rid of the H. pylori infection with antibiotics
Why is the minimal infectious dose for vibrio normally so high?
It has high sensitivity to gastric acid - any condition that increases gastric pH will lower the minimum infective dose for the bug
If a patient has alternating episodes of diarrhea and constipation, how do you differentiate between Crohn’s and IBD?
Crohn’s is more likely to have fistulas and abscesses
What type of colonic tumor appears as a cauliflower-like mass on colonoscopy?
Villous adenoma
What is the diagnosis for uncoordinated contractions of the esophagus and what work up needs to be done?
Diffuse esophageal spasms - need to do a cardiac work up to rule out angina pectoris
Mutations of what genes are responsible for Lynch syndrome?
DNA mismatch repair genes
How do we diagnose strongyloides infection?
Rhabditiform larva in the stool
In what cellular layer do we find the intrinsic factor secreting parietal cells?
Upper glandular layer (beneath the superficial layer of the lamina propria)
What is the most common location for colon adenocarcinoma?
Rectosigmoid colon
Presentation: severe heartburn, fingertip ulcerations, multiple telangiectasias - diagnosis?
CREST syndrome = calcinosis, Raynaud syndrome, esophageal dysmotility, sclerodactyly, telangiectasia
What is responsible for the esophageal dysmotility in CREST syndrome?
Atrophy and fibrous replacement of esophageal muscles
What are carcinoid tumors derived from?
Enterochromaffin cells of intestinal mucosa
Appendix biopsy shows nests/sheets of uniform cells with eosinophilic cytoplasm oval-to-round stippled nuclei - diagnosis?
Carcinoid tumor
What do you see on histology in patients with lactase deficiency?
Normal intestinal mucosa
Compared to sporadic colorectal carcinoma, how would you describe colitis associated carcinoma?
- Affects younger patients
- Progress from flat and non-polyploid dysplasia
- Histologically appear mucinous and/or have signet ring morphology
- Develop early p53 mutations and late APC gene mutations
- Be distributed within the proximal colon
- Be multifocal in nature
Bilious vomiting after the first 24 hours of life is a sign of what?
Some kind of obstruction below the second part of the duodenum
What causes intestinal atresia distal to the duodenum?
Vascular accidents in utero
Which cytokines have anti-inflammatory effects?
IL-10 and TGF-beta
question 9
come back to this
If a drug inhibits gastric acid secretion in response to all 3 stimuli (histamine, ACh, gastrin), then it likely acts where?
H/K ATPase pump on parietal cell membrane
What does 99mmTc-pertechnetate scan in the right lower abdominal quadrant indicate?
Meckel diverticulum - it detects the presence of gastric mucosa
What is the difference in antibodies produced between the killed vaccine vs. the live attenuated vaccine for polio?
Live attenuated - more IgA vs. Killed - not as good at stimulating mucosal surfaces
Describe the mechanism of diphenyoxylate.
Anti-diarrhea drug that works by binding to mu opiate receptors in the GI tract and slowing motility
What does gross morphology show for signet-ring carcinomas in the stomach?
Diffuse infiltrative growth within the stomach wall
Which picornavirus is the most acid-labile?
Rhinovirus (makes sense because the rest of them are enteroviruses so they are able to handle the acidic environment of the stomach)
What strain of E. coli is unable to ferment sorbitol/produce glucuronidase?
EHEC O157:H7
Describe the toxin produced by EHEC.
Shiga-like toxin that inactivates the 60S ribosomal subunit in human cells leading to an inhibition of protein synthesis and eventual cell death
What do the toxins produced by C. difficile do?
Toxin A - attracts neutrophils causing mucosal inflammation while Toxin B - causes actin depolymerization and loss of cellular cytoskeleton integrity
What are the 2 most common causes of acute pancreatitis?
Gallstones and alcoholism
How can hypertriglyceridemia cause acute pancreatitis?
High levels of circulating triglycerides can lead to increased production of free fatty acids within the pancreatic capillaries by pancreatic lipase. If the concentration of free fatty acids exceeds the binding capacity of albumin, then it can lead to direct injury to the pancreatic acinar cells.
What mutation facilitates the growth of adenomas by causing uncontrolled cell proliferation?
K-ras
What is a necessary cofactor in the synthesis of delta-aminolevulinic acid?
Pyridoxal phosphate
What does a duodenal ulcer in the distal duodenum suggest?
Zollinger Ellison syndrome (peptic ulcer syndrome tends to present in the first portion of the duodenum)
The longitudinal mucosal tears in Mallory Weiss syndrome are secondary to?
Rapid increase of intraabdominal and intraluminal gastric pressure (i.e. during retching and vomiting)
How many calories does 1 g of protein or carbohydrate yield?
4
How many calories does 1 g of fat yield?
9
How many calories does 1 g of ethanol yield?
7
Compression of the splenic artery most affects which branch?
Short gastric - has the worst anastomoses of all the branches of the splenic artery
How does chronic mesenteric ischemia present?
Epigastric or periumbilical pain 30-40 minutes after eating because more blood is needed for the digestion and absorption of nutrients
Patients with Barrett’s esophagus have an increased risk of which cancer?
Esophageal adenocarcinoma
What is the primary pathophysiologic mechanism for GERD?
Gastroesophageal junction incompetence
When a patient is suspected to have H. pylori, where should you biopsy?
The prepyloric area because the organism is typically found in the greatest concentration in the gastric antrum
Is B12 a fat or water soluble vitamin?
Water soluble
Presentation: Baby with poor feeding, weakness, complete loss of extremity muscle tone, and eats honey. Diagnosis?
Infant botulism
What test can be used to diagnose infant botulism?
Test stool for bacterial toxins
Presentation: Progressive weight loss, jaundice, anorexia, enlarged but non tender gall bladder. Diagnosis?
Pancreatic adenocarcinoma
What are the major risk factors for pancreatic cancer?
Old age, smoking, diabetes, chronic pancreatitis, genetic predisposition
AST:ALT > 2 is indicative of what?
Alcohol hepatitis
What do you see in terms of the mean corpuscular volume with chronic alcohol abuse?
Macrocytosis - either related to B12/folate deficiency or just from direct toxicity of alcohol on the marrow
What happens to lactose in the body?
Catabolized into glucose and galactose by an intestinal brush border disaccharidase (lactase)
What is galactosyl beta-1,4-glucose?
Lactose
What prevents overgrowth of C. diff?
Intestinal biomass (the normal flora)
Are villous or tubular adenomas more likely to progress to adenocarcinoma?
Villous
What enzyme deficiency is the second most common cause of SCID (after X linked inheritance)?
Adenosine deaminase - enzyme necessary for the elimination of excess adenosine within cells
What layer should be biopsied in Hirschsprung disease?
Submucosal (Meissner) and myenteric (Auerbach) autonomic plexi are absent in the affected segment of the bowel in Hirschsprung disease
Where do most anal fissures occur?
Posterior midline distal to the dentate line because posterior anal canal is relatively poorly perfused
Why are patients with Crohn’s disease at increased risk for gallstones?
Increased biliary acid wasting (bile acids are not reabsorbed as well in the ileum when it is affected by Crohn’s) leads to less bile acid in the bile relative to cholesterol causing cholesterol to precipitate and form stones
Why are patients with Crohn’s disease at increased risk for kidney stones?
Impaired bile acid absorption in the terminal ileum leads to loss of bile acids in the feces –> fat malabsorption –> lipids end up binding calcium –> calcium doesn’t bind oxalate –> oxalate precipitates as kidney stones
Histology of chalky white lesions in the mesentery show fat cell destruction and calcium deposition - suggestive of?
Acute pancreatitis
Abnormal rotation and fixation of what leads to intestinal malrotation?
Midgut
