GI X & XI - Functions of the Liver Flashcards
The majority of the liver’s blood supply is what?
venous blood from the GI tract via the portal vein
Describe blood flow vs. bile flow in the liver.
blood drains from liver into central branches of hepatic vein (periphery–>center), whereas bile flows from hepatocytes where it is synthesized and out to ductal system and bile duct (center–>periphery)
What does the hepatic triad consist of?
hepatic artery, portal vein, bile duct
What is the difference between zone 1, 2, and 3 cells?
- zone 1 (periportal): closest to triad (in periphery), most sensitive to oxidative injury, have largest supply of nutrients and O2, most active in detox
- zone 2: intermediate b/t zones 1 and 3
- zone 3 (pericentral): closest to hepatic vein (central), most sensitive to ischemia, most active in bile synthesis
What is the classic hepatic lobule?
drains blood from portal vein and hepatic artery to the central hepatic vein (periphery–>center); hexagonally shaped
What is the portal lobule?
drains bile from hepatocytes to the bile duct (center–> periphery)
What is the portal acinus?
supplies oxygenated blood to hepatocytes (mostly refers to zone I cells)
The liver plays which major role in carbohydrate metabolism?
gluconeogenesis, as well as glucose buffer function (stores excess glucose as glycogen and releases stored glucose into bloodstream as needed)
Patients with liver failure can develop which condition related to protein metabolism?
hypoalbuminemia - may lead to peripheral edema due to loss of peripheral protein oncotic pressure, as well as clotting disorders
What is the major constituent of bile?
bile acids (65%) - remember that bile is a complex of many constituents
Hepatocytes synthesize 2 primary bile acids:
-cholic acid
-chenodeoxycholic acid
(both are synthesized from cholesterol)
How are secondary acids produced from the 2 primary bile acids?
colonic bacterial enzymes act on the primary bile acids to yield the secondary ones (ursodeoxycholic acid, deoxycholic acid, lithocholic acid)
Why does bile need to be conjugated?
to make it more water soluble (and therefore, more absorbable)
In hepatocytes, primary and secondary bile acids are conjugated with what? What is the exception?
glycine or taurine; exception is lithocholic acid, which is preferentially sulfated
Conjugated bile acids are fully ionized in the intestinal lumen and actively absorbed in the terminal ileum via what?
apical Na+-dependent bile salt transporters (abst) - conjugated bile acids are unable to passively cross intestinal epithelial lining
The majority of the bile acid pool is _______ from the intestine back to the liver via ______ circulation.
recycled; enterohepatic
What is the role of the enzyme 7 alpha-hydroxylase?
It plays an important role in cholesterol metabolism and converts cholesterol into the 2 primary bile acids (cholic acid and chenodeoxycholic acid).
Are deconjugated bile acids able to be passively reabsorbed?
yes, but this only accounts for a minor fraction of bile acids… the majority of bile acids (conjugated) are reabsorbed by asbt symporter and recycled
What is a situation that would cause 7 alpha-hydroxylase to become more active?
a situation in which there is a lower concentration of bile acids, as 7 alpha-hydroxylase is responsible for converting cholesterol into bile acids; another possible situation is hypercholesteremia, when there is more cholesterol present for the enzyme to act on
How is bile modified?
by action of cholangiocytes lining biliary ductules
How can hypercholesteremia be improved by blocking enterohepatic circulation?
the body will allow more cholesterol and fatty material into the bile acids, which are then excreted
What are the cholesterol inputs vs. outputs?
- inputs: hepatic and extra-hepatic synthesis, diet
- outputs: cholesterol, bile acids
How and where is bile diluted?
It is diluted in the biliary ductules by the action of secretin, which stimulates aquaporins and brings water into the lumen of the bile duct.
What makes bile slightly alkaline?
the exchange of chloride and bicarbonate across the cholangiocyte membrane lining the bile duct lumen, which deposits bicarb into the bile duct
What is the major stimulus for bile secretion?
CCK, which causes contraction of the gallbladder and relaxation of the sphincter of Oddi, allowing bile into the duodenum
What is jaundice the result of?
accumulation of free and conjugated bilirubin in the blood
