Bile Flashcards
What is the unstirred water layer?
- As chyme gets near intestinal wall (enterocytes), flow becomes slower
- Enterocytes also secreting out mucus and bicarb that helps protect cell
- mucus further slows chyme
- This creates unstirred water layer
- most nutrients can get to enterocytes
- only problem with lipids (because hydrophobic)
Which nutrients aren’t able to go through stirred water layer?
- Lipids- because they’re hydrophobic, can’t get through stirred water layer on own
- need carrier- bile
How does bile help lipids to get through stirred water layer?
- By forming Micelle (think of taxi)
- take lipids through unstirred water layer and drop them off to diffuse into enterocyte
- Bile works with lipid, enzymes to create micelle
Where is bile synthesized?
Hepatocytes in Liver
hepatocytes are functional cells of liver
What forms primary bile?
- Cholic acid (main type of parimary bile)
- made from cholesterol backbone
- get cholesterol from diet
- synthesis as well
- occurs in hepatocytes through enzyme HMG CoA reductase
- also metabolic waste
- excess phospholipids
- bilirubin
- made from cholesterol backbone
How do we make cholesterol in hepatocytes?
Through HMG CoA reductase
- where statin drugs work to lower plasma cholesterol levels
Bile is ____
(how does it interact w/ water
amphipathic
because of conjugation
How do we make bile polar (hydrophilic?)
- Conjugation with taurine, glycine
- this makes it hydrophilic on one side with amino acid
- Remains hydrophobic on cholesterol end?
Around lipids, bile act as an _____
emulsifier
- acts like dish soap and makes smaller lipid droplets
- bile does not digest the lipids whatsoever, just acts like dish soap to emulsify lipid
What is secondary bile?
- Primary bile that has been acted on by intestinal bacteria
- this happens lower in intestinal tract, mainly colon
- Secondary bile not ampipathic, much more lipophilic
- hard time with getting through to enterocytes in lower part small intestine
Once bile is made where is it secreted?
Bile duct
What happens when bile is secreted into ducts?
- Pulls water and solute with it since bile is highly osmotic
- When secreting bile, effectively secreting a buffer since NaHCO3 comes with it
- called solvent drag
- Important for buffering acidic chyme out of stomach
What nerve is activated when food goes in mouth/stomach?
Activation of vagus nerve
- This increases bile production in liver
- Allows relaxation at sphincter of oddi so any small amt bile in bile duct can get to duodenum
- ramps up even more once chyme in duodenum
What happens when chyme released into duodenum?
- Presence of chyme in duodenum releases duodenal hormones
- Increases CCK into blood
- circulates and contributes more to bile production
- relaxes sphincter oddi
- start rhthmic contraction of gallbladder with stored bile
- allows bile to spurt into duodenum onto chyme
- Increases CCK into blood
Where is bile reabsorbed?
Terminal ileum
- Transporters on terminal ilieum allow bile back into enterocyte
- goes to portal system and recycles back to liver to be resecreted
How long does bile secretion/recycling continues?
As long as chyme is coming down tract and CCK secreted into blod
How much bile is lost in each cycle of recycling?
10%
What happens at end of meal?
- Once no more chyme coming down tract, secretion of CCK reduces
- this blocks spincter of oddi
- any bile recycled back, stored again in gallbladder for next meal
We rid body of cholesterol, bilirubin and waste via ____
feces
What are gallstones?
Accretion of bile
can block bile ducts and lead to emergency sx
What does CCK do?
Cholecystokinin
- released into blood once chyme coming down tract
- Stimulates bile production
- gall bladder contractions
- opens sphincter of oddi
- stimualtes secretion pancreatic enzymes
The term “bile acid” or “bile salts” are used ____
interchangably
as soon as bile acid comes near sodium, becomes a bile salt
What is progression of formation of micelles?
- Fat droplet comes in contact with bile salts, causing imulsion
- Bile salts+ pancretic lipase with co-lpase forms micelles
Micelle does not form until action of _____
pancretic lipase and co-lipase
Most of lipids come out ____ in meal
later
Lipids floating to top of stomach
What is role of pancretic lipase in micelle?
- Hydrolyzes lipids
- BUT CANNOT reach lipids by itself
- needs co-lipase in order to reach lipid ccovered in bile
What is role of co-lipase?
Co-lipase allows opening in bile so pancreatic lipase can come in
Function of gallbladder?
Dehydrates and stores bile
What happens if you remove gallbladder?
- Reduce storage of bile
- liver needs to increase production of bile
- Complications after successful sx is rare but 5-40% of patients by develop postcholecystectomy synrdome
- chornic GI distress
- pain in RUQ
- Up to 20% develop diarrhead
- more osmotic effect because more bile secreted from liver
- more bile in feces, more chance of diarrhea
What can be given to reduce diarrhea after cholecystectomy/ileal resection?
Cholestyramine
- Binds to bile and makes less osmotically active
Is there still bile recycling with gallblader removal?
Yes, but just not as good
After gallbladder removal, where does the recycled bile go?
Stays in bile duct. Not as effective storage without gallbladder
What happens to bile if ileum removes?
- Little to no recycling of bile
- bile excreted by gallbladder and liver excreted in feces
- When sphincter of oddi closes, only bile remaining in ducts is “vacuumed” into gallbladder and stored
- liver produces more bile because it does not sense any bile recycled
- Pt needs to decrease fat
- pt will get diarrhea because of increased bile in feces
- cholestyramine can also be used to help contorl diarrhea
What else is importnat about bile?
Bilirubin metabolism/excretion
Bilirubin secreted with bil is ______ with ___ ___
conjugated; glucuronic acid
What do colonic bacteria do to bilirubin?
Remove acid moiety and bilirubin is converted to urobilinogen
WHat happens to urobilinogen in colon?
- 10-20% is absorbed, recycled into portal blood, returned to systemic circulation, where it is filtered and then converted to urobilin (yellow color) and excreted into urine
- other portion urobilinogen is oxidized by intestinal bacteria to brown stercobilin
- excreted in feces
- makes feces brown
What makes your feces brown?
Stercobilin
What is urobilinogen converted to in kidney?
Urobilin
