Flashcards in Lecture 16: Lipids Deck (42):
Organic molecules that dissolve readily in organic solvents but are much less soluble in water
What are main lipid classes in body and diet
Others: vitamins ADEK, sphingolipids, saccharolipids
What are the functions of lipids?
Energy source + reserve
Major membrane constituents
Regulation of physiologic processes
What are triglycerides?
Glycerol + 3 fatty acids
What are the functions of triglycerides?
Energy transport and storage, insulation, cushioning
Which unsaturated fatty acid bonds lead to straight chains and bent chains?
Where do trans-fatty acids occur?
Cis = bent
Trans = straight
Meats + dairy products
=> inc. risk of heart disease, diabetes and breast cancer because of food processing that involves addition of hydrogens to double bonds
Which fatty acid double bonds are essential, which humans cannot make?
Omega 3 and omega 6
Omega 3 = alpha linolenic acid
Omega 6 = linoleic
Differentiate between omega-6 and omega-3 fatty acids
Omega-6 = precursors of arachidonic acid (pro-inflammatory)
Found in: seeds, nuts, meat
Omega-3 = precursors of EPA (anti-inflammatory) and DHA
Found in: fish, soybeans, walnuts
What determines inflammatory and vascular tone?
Balance of arachidonic acid and EPA/DHA-derived lipid mediators = eicosanoids
Describe short-chain fatty acids (SCFA)
Produced from fiber
Absorbed by epithelial cells and used for energy generation, allowing energy extraction from non-digestible food
Describe medium-chain fatty acids (MCFA)
Found in dairy products and certain vegetable oils (coconut, palm)
More readily absorbed and metabolized than long-chain fatty acids
Diglycerides with a phosphate-linked organic group
Multiple ring lipids derived from steroid alcohols
Contain no fatty acids
Bile acid precursor
NOT energy source
Non-essential in diet
Made by liver
Where is bile acid excreted into?
Where is it taken up again for recirculation?
Intestinal lumen via bile duct in duodenum
Describe bile acid structure and function
Hydrophobic + hydrophilic elements
Acts as detergent to emulsify lipids and make them easier to absorb
What is the only excretion pathway for cholesterol in the body?
Fecal loss of bile acids (since synthesized from cholesterol)
Describe the steps of lipid absorption
Emulsified in intestinal lumen
Broken down into more water-soluble molecules
Uptake into epithelium
Resynthesized in epithelial cells and exported to circulation
What helps emulsify large lipid droplets into smaller ones?
Peristalsis in the stomach and small intestine
Bile acid as detergents
How are triglycerides digested?
Hydrolyzed to free fatty acids and monoglycerides or glycerol by lipases
What three lipases help with triglyceride digestion?
What is lingual lipase secreted by ?
"Von Ebner" serous glands on tongue
Which lipase is important for infant nutrition and adults with pancreatic insufficiency?
What is gastric lipase secreted by?
Chief cells in gastric glands
What is gastric lipase inhibited by?
Bile acids in small intestine
What is pancreatic lipase secreted by?
Pancreatic acinar cells, released in pancreatic juice into duodenum
At what pH is gastric lipase activity optimal?
At what pH is pancreatic lipase activity optimal?
Do gastric lipase and pancreatic lipase require cofactors for activity?
Gastric lipase = no
Pancreatic lipase = pancreatic co-lipase (to anchor)
What is the product of phospholipase A2 (PLA2) activity?
What is PLA2 secreted by?
Pancreatic acinar cells as a zymogen
Proteolytically activated in intestinal lumen
Describe the digestion of cholesterol that must take place before dietary cholesterol can be absorbed in intestine.
How efficient is this process?
Hydrolyzed to remove ester, resulting in cholesterol + fatty acid
What are potential pathways for fatty acid uptake into intestinal epithelial cells?
Passive intestinal uptake of fatty acids -
Differentiate between paracellular and transcellular uptake and which is the more difficult of the two
Paracellular uptake through tight junctions
**Transcellular uptake across epithelial cell
**more difficult because would require "flipping" of lipids in order to integrate into apical sheet of lipid belayer
What are cytoplasmic fatty acid-binding proteins?
Sequester fatty acids as soon as they cross membrane
Important for transport of fatty acids to specific target within the cell
Act as lipid sensors
What is NPC1L1?
Protein that acts as a cholesterol receptor to mediate uptake by endocytosis
Describe epithelial lipid processing.
Cholesterol is re-sterilized
Phospholipids are resynthesized
Monoglycerides/fatty acids converted back to TG's
How are re-synthesized lipids exported?
Assembled with apolipoproteins to form chylomicrons
Chylomicrons are too big for capillaries, so they exit through lympathic vessels
How does the exit route differ for medium chain and long chain fatty acids?
Medium = portal vein
Long = lymphatic
Distinguish efficiencies of intestinal uptake for monoglycerides, fatty acids, glycerol, and sterols
Very efficient = monoglycerides, FA's, glycerol
Less efficient = sterols
Why are bile acids critical for lipid emulsification?
They associate with TG's to form micelles
Micelles allow greater access of pancreatic lipases to free the FA's
FA's, once freed, are then able to be actively taken up by epithelial cells