Bile acids

Question 1

Components of bile

Answer 1

water
phosphatidyl choline
bile salts
bilirubin
inorganic salts

Question 2

Function on bile

Answer 2

emulsifying fats
neutralize acids in stomach
bile salts as bactericides, destroy micobs in food
bile is route of excretion of bilirubin

Question 3

Bile acids

Answer 3

24 carbon chain
2-3 OH groups and 1 COOH
amphipathic- polar and non-polar face
synthesized in liver

Question 4

Bile salts

Answer 4

conjugated bile acids:
bile acid + glycine
bile acid + taurine

pKa reduces
fully ionized in physiological pH

Question 5

Primary bile acids

Answer 5

cholic acid + chenodeoxycholic acid
-synthesized i hepatocytes
conjugated to primary bile salts in liver peroxisomes

Question 6

Bile in GI

Answer 6

Bile via common bile duct to duodenum

• alot absorbed in ileum- enterohepatic circulation
• some to colon - many anaerobic bacteria - deconjugate the salts - Secondary bile acids/salts

Question 7

Secondary bile acids

Answer 7

deoxycholic acid + lithocholic acid
deoxycholic absorbed in colon and reconjugated in liver
lithocholic poorly absorbed, excreted with feces

Question 8

Cholesterol -> 7 alpha hydroxycholesterol

Answer 8

cholesterol + O2 + NADPH + H+ -> 7alpha hydroxycholesterol + NADP+

• enzyme: 7 ALPHA HYDROXYLASE
• requires vitamin C

Question 9

Regulation of 7 alpha hydroxylase

Answer 9

negative feedback loop

regulated via farnesoid X receptor (FXR) (nuclear bile acid binding receptor)

Question 10

7 alpha hydroxycholesterol -> Cholyl CoA + Chenodeoxycholyl CoA

Answer 10

+O2,NADPH +H+, 2CoASH

• proprionyl-CoA
  enzyme: 12 ALPHA HYDROXYLASE