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
