Flashcards in LIVER - BILE Deck (20)
what are the functions of bile?
- removal of lipid soluble xenobiotics/drug metabolites/heavy metals
- induce bile flow and secretion of biliary lipids
- digestion of dietary fats
- facilitates protein absorption
- cholesterol homeostasis
- prevents calcium gallstones and oxalate renal stones
how does bile acid maintain cholesterol homeostasis?
it facilitates dietary absorption/elimination as bile acids are water-soluble end products of cholesterol catabolism
it enables the movement from hepatocyte to intestinal lumen
how do bile acids facilitate protein absorption?
accelerates hydrolysis by pancreatic proteases
how does bile acids facilitate digestion of dietary fats?
by solubilising lipids and lipid digestion products as mixed micelles facilitating aqueous diffusion across the intestinal mucosa
what is the composition of bile acid?
what is the composition of hepatic/gallbladder bile?
2/3 bile is bile acids (cholic, chenodeoxycholic, deoxycholic,lithocholic and ursodeoxycholic)
1/4 is phospholipids
small amounts of cholesterol, bilirubin and proteins
what is the composition of faecal bile acids?
how much bile is produced per day?
what happens to bile in fasted state?
bile acids travel down the biliary tract to the gallbladder where it is concentrated 10-fold
what happens to bile in the fed state?
CCK is released from duodenal mucosa and stimulates release of bile
what are the effects of CCK?
relaxes sphincter of oddi
contracts gall bladder
releases concentrated solution of mixed micelles (bile acids, phospholipids and cholesterol)
how is bile reabsorbed?
conjugated bile acids remain intraluminal
they are actively transported via apical sodium bile transporter in the ileum
it re-enters the liver via the portal system
the bile acids are reconjugated and secreted into biliary canaliculi
what happens in the feedback system for bile production?
bile acids are a ligand for farnisoid X receptor in ileum
this results in the synthesis of FGF-19
this inhibits CYP7A1 (the enzyme required bile production)
what is the effect of statins on cholesterol production?
statins inhibit HMG CoA reductase - this stops cholesterol from being formed
what happens to cholesterol in the body?
50% is absorbed and 50% is excreted
what is the effect of ezetimibe on cholesterol?
it stops protein mediated transport of cholesterol across the enterocyte membrane
which enzyme is required for bile acid synthesis?
what are the effects of bile acid conjugation?
it increases hydrophilicity
increases acidic strength of side chain
decreases passive diffusion of bile across cell membranes - keeps it intraluminal
what is the effect of intestinal bacteria on bile acids?
converts them into secondary bile acids