Fat and Lipoprotein digestion Flashcards
What are fatty acids?
various lengths of carbon chains saturated or unsaturated with hydrogen
What are the type of fatty acids?
short chain volatile fatty acids, medium chain, or long chain
What is pharyngeal lipase?
a lipase secreted by the salivary glands that has a high affinity for the micellar structure of milk fat; only important in newborns
What is the role of the stomach in lipid digestion?
emulsification of fats with chyme by churning action of the stomach
What is emulsification?
to suspend one liquid in another (fat droplets in water or chyme)
What pancreatic enzymes are important in fat digestion?
pancreatic lipase and colipase
What fats does pancreatic lipase help digest?
triglycerides to monoglycerides, diglycerides, and free fatty acids
What does pancreatic lipase need to be activated?
it can only bind to fat in the presence of colipase and bile salt
When does pancreatic lipase work on fats?
it acts on fats that are in emulsion - works at water/fat interface
What is the precursor for colipase?
procolipase- cleaved by trypsin
Why can short chain fatty acids reach the intestinal brush border?
because they are water soluble enough that they can cross the unstirred water layer and glycocalyx to reach it
How do short chain fatty acids cross the apical and basal lateral membranes?
via non-ionic diffusion
What is non-ionic diffusion?
when weak acids and bases cross the membrane in their non-dissociated form and reassociate on the other side
How do short chain fatty acids move into extracellular fluid and portal circulation?
via passive diffusion down their concentration gradient
What is a detergent?
one end of the molecule is hydrophobic which allows it to from ionic bonds with hydrophobic fatty acids, the other end is very hydrophilic making the fatty acid fairly water soluble
What pancreatic enzymes work with bile salts on the emulsified fat?
pancreatic lipase, colipase, and cholesterol ester hydrolase
What does colipase allow for?
the formation of cross bridge between lipase and bile salts
What does cholesterol ester hydrolase do?
removes ester groups from cholesterol esters and lipid esters
What is a micelle?
water soluble packages of fatty acids, monoglycerides, cholesterol, and vitamins A, D, and E
What do micelles do?
carry the lipid load to the cell surface across the unstirred water layer to bilipid cell membrane where the lipid soluble fatty acids, monoglycerides, and cholesterol can diffuse freely
What happens to the bile salts that carry lipids away from fat droplets?
they are too water soluble so they re-enter the lumen and grab another load of lipids
What do intestinal epithelial cells do?
secrete intestinal lipase
What does intestinal lipase do?
converts any remaining di-triglyceride to mono-glycerides and fatty acids to finish fat digestion
What happens to fatty acids once they are taken into the endoplasmic reticulum of the epithelial cells?
they are converted back into triglycerides
How do newly formed triglycerides maintain the fatty acid gradient from intestinal lumen to cell cytosol?
they lower the free fatty acid within the cytosol once they are created
How do the newly formed triglycerides get out of the intestinal cells into the blood?
they are packaged into chylomicrons to cross the basal lateral membrane of the epithelial cell
What are chylomicrons made up of?
80% triglyceride, vitamin A, D, E, 9% phosphoglycerides, 3% cholesterol, and 2% lipoprotein
What is the purpose for the lipoprotein in the chylomicron?
they are on the outside of it so it makes the whole globule water solumble enough to move into the extracellular fluid
Chylomicrons are too big to enter the portal venous system, so where do they go?
they are picked up by the lacteals and enter general circulation through the thoracic duct
What is enterohepatic circulation?
when bile salts reach the ileum, go across it and enter the portal blood where they are extracted by liver cells and put back into bile ducts
What can cause a loss of bile acids?
diarrhea - flushed out
What will a loss of bile acids do?
lead to poor fat digestion
In circulation, what do chylomicrons gain and from what?
they get apolipoprotein C and E from high density lipoprotein carriers
What does apolipoprotein C do?
it allows for the chylomicron to bind to Apo C receptors on adipose, mammary, skeleral and heart muscle, and liver where it releases its triglycerides
What is a VLDL?
a package used to transport triglyceride and cholesterol out of the liver - can deliver triglycerides to peripheral tissue
What is a LDL?
a remnant of VLDL - still has lots of cholesterol which it can deliver ot tissue - bad cholesterol
What is a HDL?
a high density lipoprotein carrier that can exchange apo C and E with chylomicrons and VLDL, can also pick up triglycerides from chylomicrons
