GI path

Question 0

infectious bacteria that affect the proximal colon

Answer 0

1. Salmonella
2. yersinia -> pseudoTB
3. TB

Question 1

Infectious causes of diarrhea

Answer 1

1. damage epithelial cells: Rotavirus, Norwalk virus (both sm. intestine)
2. PREformed toxins: vibrio, staph aureus, clostridium perfringens
3. toxigenic: E. coli, shigella

Question 2

bacteria that affect the distal colon

Answer 2

1. shigella
2. E coli *risk HUS as complication! (can be deadly)
3. Campylobacter

Question 3

Liver Cirrhosis signs (triad)

Answer 3

1. diffuse involvement
2. fibrosis
3. regenerative nodules (abnormal)
   (gross: hard, nodular, atrophic liver)

Question 4

Bile acid uses

Answer 4

1. cholesterol catabolism
2. stimulate bile flow
3. absorb dietary cholesterol (as mixed micelle w/ lecithin in gut)
4. cholesterol solubilization
5. Treatment of gallstones, SIBO, primary biliary cirrhosis…

Question 5

cholesterol 7a-hydroxylase

Answer 5

Enzyme that converts cholesterol to 1st intermediate of bile acid synth.
= rate limiting step for bile acid synthesis
* Inhibited by bile acids
* stimulated by cholesterol

Question 6

Bile acid synthesis (steps, results)

Answer 6

1. @ Liver: Cholesterol –> 1st intermed by cholesterol 7a-hydroxylase
2. @ intestinal lumen: 2 different intermediates modified => bile acids (cholic & chenodioxycholic acids)
3. @ liver: bile acids conjugated & stored

Question 7

Liver transporters for Bile Acids

Answer 7

• NTCP & OATP: transport bile salts from plasma into hepatocyte
  (“Na+ Taurocholate Cotransporter” & “Organic Acid Transporter”)
• BSEP: transports bile salts from hepatocyte into bile canaliculus

Question 8

Intestinal bile acid transporter

Answer 8

ASBT: “Apical Sodium-dep. Bile Transporter”
transports bile salt w/ Na+ into terminal ileocyte from gut lumen
(for recycling back to liver, 95%)

Question 9

3 states of cholesterol (w/ bile acids)

Answer 9

1. Mixed Micelle: bile acid clump w/ lecithin-cholesterol vesicles in middle; = stable & soluble.
2. Vesicle: just lecithin & cholesterol; ~”metastable”
3. Cholesterol crystals: only cholesterol, precipitates => gallstones

Question 10

Causes of gallstones

Answer 10

1. high lipids
   a) increased cholesterol intake/secretion
   b) decreased bile salts
2. short nucleation time

Question 11

Chenodeoxycholic acid vs. Ursodeoxycholic acid

Answer 11

Chenodiol: decrease cholesterol secretion, & increases bile acid pool at HIGH doses. *SE: hepatoxicity, diarrhea, high serum cholesterol

#1 Ursodiol: same mech as chenodiol + increase nucleation time & decrease crystal precipitation. *NO SEs! 
(hepatoprotective bc inhibits apoptosis)

Question 12

Therapeutic uses of Ursodiol

Answer 12

1. cholelithiasis (gallstones)
2. primary biliary cirrhosis
3. Intrahepatic cholestasis of pregnancy
4. SIBO (sm intestine bacterial overgrowth)

Question 13

SIBO (Small Intestinal Bacterial Overgrowth)

Answer 13

diarrhea/steatorrhea; likely to cause stasis of small bowel

=> vit B12 deficiency & decreased bile salt absorption/recycling