GI X & XI - Functions of the Liver

Question 1

The majority of the liver’s blood supply is what?

Answer 1

venous blood from the GI tract via the portal vein

Question 2

Describe blood flow vs. bile flow in the liver.

Answer 2

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)

Question 3

What does the hepatic triad consist of?

Answer 3

hepatic artery, portal vein, bile duct

Question 4

What is the difference between zone 1, 2, and 3 cells?

Answer 4

• 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

Question 5

What is the classic hepatic lobule?

Answer 5

drains blood from portal vein and hepatic artery to the central hepatic vein (periphery–>center); hexagonally shaped

Question 6

What is the portal lobule?

Answer 6

drains bile from hepatocytes to the bile duct (center–> periphery)

Question 7

What is the portal acinus?

Answer 7

supplies oxygenated blood to hepatocytes (mostly refers to zone I cells)

Question 8

The liver plays which major role in carbohydrate metabolism?

Answer 8

gluconeogenesis, as well as glucose buffer function (stores excess glucose as glycogen and releases stored glucose into bloodstream as needed)

Question 9

Patients with liver failure can develop which condition related to protein metabolism?

Answer 9

hypoalbuminemia - may lead to peripheral edema due to loss of peripheral protein oncotic pressure, as well as clotting disorders

Question 10

What is the major constituent of bile?

Answer 10

bile acids (65%) - remember that bile is a complex of many constituents

Question 11

Hepatocytes synthesize 2 primary bile acids:

Answer 11

-cholic acid
-chenodeoxycholic acid
(both are synthesized from cholesterol)

Question 12

How are secondary acids produced from the 2 primary bile acids?

Answer 12

colonic bacterial enzymes act on the primary bile acids to yield the secondary ones (ursodeoxycholic acid, deoxycholic acid, lithocholic acid)

Question 13

Why does bile need to be conjugated?

Answer 13

to make it more water soluble (and therefore, more absorbable)

Question 14

In hepatocytes, primary and secondary bile acids are conjugated with what? What is the exception?

Answer 14

glycine or taurine; exception is lithocholic acid, which is preferentially sulfated

Question 15

Conjugated bile acids are fully ionized in the intestinal lumen and actively absorbed in the terminal ileum via what?

Answer 15

apical Na+-dependent bile salt transporters (abst) - conjugated bile acids are unable to passively cross intestinal epithelial lining

Question 16

The majority of the bile acid pool is _______ from the intestine back to the liver via ______ circulation.

Answer 16

recycled; enterohepatic

Question 17

What is the role of the enzyme 7 alpha-hydroxylase?

Answer 17

It plays an important role in cholesterol metabolism and converts cholesterol into the 2 primary bile acids (cholic acid and chenodeoxycholic acid).

Question 18

Are deconjugated bile acids able to be passively reabsorbed?

Answer 18

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

Question 19

What is a situation that would cause 7 alpha-hydroxylase to become more active?

Answer 19

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

Question 20

How is bile modified?

Answer 20

by action of cholangiocytes lining biliary ductules

Question 21

How can hypercholesteremia be improved by blocking enterohepatic circulation?

Answer 21

the body will allow more cholesterol and fatty material into the bile acids, which are then excreted

Question 22

What are the cholesterol inputs vs. outputs?

Answer 22

• inputs: hepatic and extra-hepatic synthesis, diet

- outputs: cholesterol, bile acids

Question 23

How and where is bile diluted?

Answer 23

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.

Question 24

What makes bile slightly alkaline?

Answer 24

the exchange of chloride and bicarbonate across the cholangiocyte membrane lining the bile duct lumen, which deposits bicarb into the bile duct

Question 25

What is the major stimulus for bile secretion?

Answer 25

CCK, which causes contraction of the gallbladder and relaxation of the sphincter of Oddi, allowing bile into the duodenum

Question 26

What is jaundice the result of?

Answer 26

accumulation of free and conjugated bilirubin in the blood