Liver Physiology (Johnson/Costanzo) Flashcards
What causes ascites with liver failure?
liver responsible for protein synthesis; in failure, decr oncotic pressure = ascites
Cholesterol is used the synthesize:
bile acid
Secretin stimulates:
secretion of bicarb and water into the ducts
In gallbladder, bile concentrated via:
active absorption of Na, Cl, bicarb, water
What are the functions of CCK? What do these cause?
contraction of the gallbladder
relaxation of the sphincter of Oddi
**causes stored bile to flow from the gallbladder into the lumen of the duodenum
How does the timing of GB contractions relate to duodenal contractions?
they coincide
The hepatocytes of the liver (intermittently/continuously) synthesize and secrete the constituents of bile.
continuously
The components of bile are:
the bile salts, cholesterol, phospholipids, bile pigments, ions, and water.
What is the function of the GB?
- store bile
- concentrate bile salts (by absorption of water and ions)
- eject bile (~30min after meal)
What signals the secretion of CCK?
chyme reaching the small intestine
In the small intestine, the bile salts function in:
emulsifying and solubilizing dietary lipids
What happens to bile salts once they’ve done their business?
When lipid absorption is complete, bile salts are recirculated to liver via enterohepatic circulation
(where they are actively extracted from portal blood)
How are bile acids reabsorbed?
40% of bile acids/salts are reabsorbed via passive diffusion
55% of bile acid/salts are actively reabsorbed in the ilium (contains specific receptors for bile acids/salts, Na dependent process)
Decreased reabsorption of bile acids results in:
increased bile acid synthesis
Bile acids returning from circulation inhibit:
bile acid synthesis via 7-beta-hydroxylase inh
(negative feedback)
**The liver must replace only the small percentage of the bile salt pool that is excreted in feces
Two primary bile acids (synthesized by liver):
What happens to primary bile acids once secreted into lumen of intestines?
Cholic acid
Chenodeoxycholic acid
portion of each is dehydroxylated by intestinal bacteria to produce 2 secondary bile acids
4 Bile acids, in order of greatest relative amount to least:
Cholic acid > chenodeoxycholic acid > deoxycholic acid > lithocholic acid
How does conjugation of bile acids in the liver change them?
conjugation to amino acids changes the pKas of bile acids and causes them to become much more water soluble
**there’s an additional explanation of this in the text that’s good
A “bile salt” is a…
bile acid conjugated with an amino acid
The most likely bile acid to be reabsorbed is the one that is the most _____
lipophilic
The critical property of bile salts is that they are ____.
Why is this significant?
amphipathic
allows them to form micelles and forms lipid droplets that repel, which increases surface area for digestion
A change in the critical micellar concentration leads to:
precipitation of gallstone
Micelles solubilize:
the products of fat digestion
fat soluble vitamins (which is why decr bile acids»_space; vit deficiency)
Micelles are comprised of:
4 different bile salts
phospholipids
cholesterol
Once the substance has been made soluble, what is the physiologic function of micelles?
bring fat digestion products close to the gut wall, allowing for absorption
- Hepatocytes extract bile acids from the:
2. It is then transported into _____ which drain into bile ducts.
portal vein
canaliculi
How does bile flow related to portal blood flow?
countercurrent, which decreases concentration gradient
How do bacteria affect the bile acids/salts in the duodenum?
deconjugate and dehydroxlate = less water soluble, which allows passive absorption to occur along length of gut
How are bile acids/salts reabsorbed?
passively, along length of gut (45%)
actively in ileum
**5% lost in feces
Interruption of enterohepatic system can lead to:
bile acid deficiency
Mechanism by which bile acids are extracted from portal blood:
Specialized Na/BA cotransporter extracts BA from blood, which requires Na/K/ATPase pump
BA then secreted into bile canaliculus via specialed BA carrier
Secretion of bile acids osmotically drives secretion of:
water+electrolytes into bile
Mechanism by which bile acids are extracted from portal blood is regulated by:
the presence of BA (NOT nerves or hormones)
How is bilirubin produced?
During metabolism of RBC (in RES):
- Removal of iron
- Reduction forms Biliverden (green pigment)
- Further reduction to bilirubin (yellow pigment)
Upon entering the blood, bilirubin is:
bound by plasma albumin and transported to liver
Bilirubin actively extracted from…
albumin
Why is bile yellow?
bilirubin glucuronide
liver extracts bilirubin and conjugates it with glucuronic acid to form bilirubin glucuronide, which is secreted into bile
Intestinal bacteria converts bilirubin to:
urobilinogen
urobilinogen can ultimately end up…
3
recirculated to the liver
excreted in the urine (gives its color, urobilinogen oxidized in kidney)
oxidized to urobilin and stercobilin, the compounds that give stool its dark color
Pale poop is the result of…
no bilirubin
T/F: During contraction of GB, the micelles break apart.
F: Throughout this process, the bile acid/salts, phospholipids, cholesterols remain in micelles.
How is normal bile different from bile in patients with cholesterol stones?
cholesterol stones: bile supersaturated with cholesterol + not enough bile acids
nml: only 50% saturated
Obese patients with cholesterol stones: ____ is increased
Non-obese patients with cholesterol stones: ____ are decreased
cholesterol
phospholipids
Most gallstones are _____ stones
cholesterol
Pigment stones consist primarily of _____
These stones will precipitate out with ______.
bilirubin
calcium
What cause pigment stones? What does this damage?
bacteria containing beta glucuronidase (deconjugates bilirubin)
GB wall damaged by bacteria
How bile acid secretion change following a cholecystectomy?
decreased secretion following meal
How does hepatic bile secretion change (following a meal) if enterohepatic circulation interrupted?
Bile acids present are only those being synthesized
incr in volume and bicarb due to secretin
