Flashcards in Topic 13: Lipid Digestion, Absorption and Trafficking Deck (57)
What is it about Bile Acids/Salts that help with lipid digestion?
Bile Salts act as detergents, emulsifying lipids. This allows the lipases to access and digest the lipids.
Lipases can only act on the surface (lipid-water interface) of a lipid.
Increases surface area for lipase action.
What are Bile acids derived from?
What does their structure look like?
Cholesterol (3 bedrooms and a bath...)
What are the PRIMARY Bile Acids?
Cholic Acid and Chenodeoxycholic Acid
What are the SECONDARY Bile Acids?
Cholic --> Deoxycholic Acid
Chenodeoxycholic --> Lithocholic Acid
Which Bile Acid is the one least able to be reabsorbed and lost in the feces?
What AAs are bile acids conjugated with?
Glycine and Taurine
What does conjugation do to Bile Acids?
Why is Taurine essential for kitties?
They favor making Taurine conjugated Bile Acids
What else is secreted with Bile Acids/Salts?
Water, Cholesterol, Phosphatidyl Choline (lecithin), Bilirubin, and Bile
From the liver, where does bile go?
Liver --> Common Bile Duct --> Duodenum
If you don't need Bile it will back up and flow through the Cystic Duct and into the Gall Bladder.
What hormone causes secretion of Bile from the Gall Bladder?
What is the functional unit of lipid?
What tissues secrete lipases?
Salivary glands, Stomach, Pancreas
How do salivary/gastric lipases digest lipids?
TAG --> DAG + FFA
accounts for about 1/3 of lipase activity in adults
Work optimally at acidic pH
How do pancreatic lipases digest lipids?
TAG --> 2-MAG + 2FFA
2-MAG just means the middle FA is still attached to the glycerol backbone and the ends have been freed.
Bile Salt Dependent (BSL)
Where are Bile Acids reabsorbed and approximately how much is conserved?
Ileum -- 90-99% reabsorbed (reduce, reuse, recycle)
Which Lipases are Bile Salt Dependent?
Breast Milk of primates and other animals
Important for NEONATES to aid lipid digestion.
What is enterohepatic ciruclation in reference to?
the recycling of Bile Acids/Salts
What lipase is inhibited by bile acids?
CDL: Colipase Dependent Lipase
It is allosterically activated by Colipase
What is PRPL-2?
Pancreatic Lipase Related Protein.
It is Colipase dependent just as CDL is.
Hydrolyzes TAG, phospholipids, and Galactolipids.
Important in NEONATES.
What does colipase do?
It helps Lipase BIND to the surface of emulsion droplets.
What results from lipase and bile acid action?
What is in a mixed micelle?
LCFA, 2-MAG, lysolecithin, cholesterol, fat soluble vitamins (A,D,E,K)
What happens to mixed micelles upon absorption into an enterocyte?
LCFA attached to CoA for activation --> Fatty Acyl-CoA
They are then either:
added to glycerol backbones (MAG or DAG) to regenerate TAGs.
added to Glycerol-3-P to generate Phosphatidic Acid (then more added to generate DAG then TAG)
added to lysolecithin to generate Lecithin
added to Cholesterol to generate Cholesterol Ester
All of which are incorporated into Chylomicrons
How are MCFA and SCFAs absorbed?
They can cross directly through an enterocyte and into hepatic portal circulation
What is in a chylomicron?
TAGs, Lecithin, Cholesterol Ester, Fat Soluble Vitamins (A,D,E,K)
What happens to Bile Acids when mixed micelles are absorbed?
Bile Acids are left behind and reabsorbed in the distal ileum.
What is the function of APO-B48 protein in the chylomicron lipoprotein?
Export by exocytosis from enterocytes through basal membrane