Lipid Digestion Flashcards
Adults typically consume
~81 grams of lipids per day
90% of the lipids consumed are
TAG (72 g)
The other 10% of lipids consumed are
cholesterols, cholesterol esters, phospholipids, free fatty acids
______ are acid-stable lipases that function in the stomach at optimal pH between pH 4 to pH 6
Acid lipases
What are the two types of Acid-Lipases?
Lingual Lipase and Gastric Lipase
____ are secreted from the glands at the back of the tongue.
Lingual Lipase
_____ are secreted from the gastric mucosa
Gastric Lipase
Acid Lipases target TAG containing _________ Fatty Acids. Give an example.
Short and Medium Chain Fatty Acids
Milk Fat
When are acid lipases especially important?
Neonates when milk is the primary food source
Name the two complementary actions of the emulsification of dietary lipids.
Mechanical Agitation and Bile Salt Secretion
_______ of dietary material via peristalsis increases the lipid droplet surface area
Mechanical Agitation
_______
- made in the liver
- stored in the gall bladder
- secreted to the small intestine
- have detergent properties that stabilize particles as they become smaller, preventing them from coalescing.
Bile Salts
Enzymes secreted from the pancreas digest dietary ____, ______ and _____
TAG, cholesteryl esters, phospholipids
_____ is the removal of specific fatty acids by breaking ester bonds attaching the fatty acids
Digestion
Name the pancreatic enzymes important for TAG digestion
Pancreatic Lipase and Colipase
This pancreatic enzyme is extremely active (high catalytic efficiency), and represents 2 to 3% of total protein in pancreatic secretions.
Pancreatic Lipase
____ is an esterase, cleaves FA at carbon-1 and -3 of the glycerol backbone producing 2 free fatty acids (thus producing a 2-monoacylglycerol)
Pancreatic Lipase
Colipase is also secreted from the pancreas and binds pancreatic lipase at a _____ ratio.
1:1
The function of ___ is to anchor pancreatic lipase at the lipid-aqeuous interface to promote pancreatic lipase enzymatic activity when inhibitory bile salts are present
Colipase
Dietary Cholesterol is present in two forms:
85-90% ______ cholesterol (free)
10-15% ______ cholesterol (cholesteryl ester)
unesterified, esterified
_______ is a pancreatic enzyme secreted to the small intestine, it digests esterified cholesterol (cholesteryl esters)
Cholesterol esterase
Cholesterol esterase produces _____ and _____
cholesterol and free fatty acids
Cholesterol esterase makes all of the cholesterol produced ______
nonesterified
Bile salts promote _____ activity
cholesterol esterase
Ingested phospholipids are digested by sequential removal of fatty acids by two different pancreatic enzymes, _______ and _______.
Phospholipase A2 and Lysophospholipase
_____ removes the fatty acid from position 2 to produce lysophospholipid and a free fatty acid
Phospholipase A2
_______ removes the fatty acid from position 1 to generate 1 fatty acid and 1 glycerylphosphoryl base
Lysophospholipase
Glycerylphosphoryl bases can be:
absorbed, further digested or excreted in the feces
What does the digestion of phospholipids produce?
2 fatty acids and 1 glycerylphosphoryl base
_________ in the mucosa of the lower duodenum and jejunum sense:
- lipids and partially digested proteins
- low pH of chime entering the intestine
Gut Endocrine Cells
What do Gut Endocrine Cells secrete into the blood?
-2 small peptide hormones: CCK and secretin
________ is a small peptide hormone secreted to the blood in response to the presence of lipid and partially digested proteins
cholecystokinin (CCK)
_______:
- promotes pancreatic enzyme secretion
- causes gall bladder to release bile
- bile salts
- phospholipids
- free cholesterol
CCK
_______;
decrease gastric motility, reducing release rate of gastric contents to the small intestine
CCK
_____: small peptide hormone secreted to the blood in response to the low pH of chime entering the intestine
Secretin
______ promotes the release of bicarbonate rich solution from the pancreas to the small intesting, providing the appropriate pH for optimal pancreatic enzyme function
Secretin
Lipid digestion in the jejunum generates 3 primary products:
- free fatty acids
- free cholesterol (very marginal)
- 2-monoacylglycerol
______:
- disk shaped clusters of amphipathic lipids
- formed from these three products (cholesterol, fatty acids, 2-monoacylglycerol) and fat-soluble vitamins (A,D,E,K)
Micelles
________: Intestinal Mucosal Cells
Enterocytes
Mixed Micelles are soluble in the intestinal lumen, and can associated with the brush border membrane of enterocytes where they are ______
absorbed
_______, relative to other dietary lipids are poorly absorbed by enterocytes
Cholesterol
____ and _______ can be absorbed directly by enterocytes without mixed micelles
short and medium chain fatty acids
The absorbed mixture of lipids is processed at the ______, the site for complex lipid biosynthesis
endoplasmic reticulum
__________: converts LCFA to their activated form by using energy from ATP-> AMP to form fatty acyl-CoA
Fatty acyl-CoA synthetase/Thiokinase
______: 2-monoacylglycerol is converted to TAG by an enzyme complex that sequentially adds activated fatty acids (above) by two enzymatic acyltransferase activities
TAG synthase
______ esterifies cholesterol with a fatty acid
acyl CoA: cholesterol acyltransferase
_____ are reacylated by a family of specific acyltransferases to form phospholipids
Lysophospholipids
______ and ______ are not activated, but are released into the portal circulation, and likely carried by serum albumin to the liver
short and medium chain fatty acids
TAG and cholesteryl esters are hydrophobic and thus need to be packaged into stable lipid droplets, called ________, to be secreted by intestinal enterocytes
chylomicrons
in ________, TAG and cholesteryl esters are surrounded by a spherical single layer of phospholipids, cholesterol and apoliprotein B-48
chylomicrons
______: lymph that contains chylomicrons
chyle
Describe the route that chyle takes.
Enterocytes–>Lymph–>Blood–>Cells
_________ are:
- produced at the ER of the enterocytes
- exocytosed into the lacteals (lymphatic vessels that origniate at the villi of the small intestine)
Chylomicrons
________:
- enzymatically degrades TAG in the circulating chylomicrons to free fatty acids and glycerol
- is synthesized and secreted primarily by muscle and adipose tissues (heart, lung, kidney, liver)
- associates with the lumen endothelial cells of capillary beds
Lipoprotein lipase
The free fatty acids are generally taken up immediately by the ______ and ______.
Adjacent Muscle and Adipose Tissue
If the free fatty acids are not taken up by the adjacent muscle and adipose tissue, they will circulate in association with _____ until taken up
serum albumin
Glycerol is taken up by the ____ and used to produce glycerol 3-phosphate which can enter glycolysis or GNG
liver
Most of the materials are hydrolyzed to their component parts, but _____ and _____ are recycled.
nitrogenous bases and phospholipids
_____ is an autosomal recessive disease with varying degrees of severity and multiple alleles.
cystic fibrosis
Cystic Fibrosis is termed pancreatic infufficiency, which results in ____ and _____
significant reduction in dietary calories and decreased fat-soluble vitamin up-take
What is the treatment for CF?
-enzyme replacement and fat-soluble vitamin supplements
Most fatty acids in the diet are ______
esterified
