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Lipid Digestion and Absorption
Terms in this set (68)
Us adult consumption of lipids
81 g/day, 90% triaglycerol (72 g. TAG)
the rest is: cholesterol, cholesterol esters, phospholipids, free fatty acids
acid-stable lipase function in the stomach at optimal pH 4 to pH 6
secreted from glands at the back of the tongue
secreted from the gastric mucosa
Enzyme action in the stomach
they target TAG containing short and medium fatty acids (<12 carbons) example: milk fat
Enzyme action in the stomach is especially important in....when milk is the primary food source
Emulsification of dietary lipids is the combination of...
two complementary actions
What are the two complementary actions of the emulsification of dietary lipids?
mechanical agitation and bile salts secretion
of dietary material via persistalis increases the lipid droplet surface area
Bile salts secretion
made in the liver, stored in the gallbladder, secreted to the small intestine, have detergent properties that stabilize particles as they become smaller, prevents them from coalescing
Enzymes secreted from the pancreas...
digest dietary TAG, cholesterol esters and phospholipids
the removal of specific fatty acids by breaking ester bonds attaching the fatty acids
TAG is too big for intestinal mucosal cells to endocytose efficiently
an esterase, cleaves fatty acids at carbon 1 and carbon 3 of the glycerol backbone producing 2 free fatty acid: a 2 monoaclyglycerol, represents 2 to 3% of total protein in pancreatic secretions, has high catalytic efficiency
is also secreted from the pancreas and binds
pancreatic lipase ast a 1:1 ration
Function of collapse
to anchor pancreatic lipase at the lipid-aqueous interface to promote pancreatic lipase enzymatic activity when inhibitory bile salts are present
Cholesteryl ester digestion
dietary cholesterol is present in two forms
What are the two forms dietary cholesterol is present in?
85-90% nonesterified cholesterol (free)
10-15% esterified cholesterol (cholesteryl ester)
a pancreatic enzyme secreted to the small intestine, it digests esterified cholesterol (cholesteryl esters)
Cholesterol esterase is involved in...
producing cholesterol and free fatty acids, all cholesterol is finally non esterified
Bile salts promote..
cholesterol esterase activity
ingested phospholipids are digested by sequential removal of fatyy acids by two different pancreatic enzymes, producing two fatty acids and one glycerylphosphoryl base
removes the fatty acid from position 2 to produce lysophospholipid and a free fatty acid
removes the fatty acid from position one to generate one fatty acid and one glycerylphosphoryl base
Glycerylphosphoryl bases can be..
absorbed, further digested, and excreted int he feces
GUT ENDOCRINE CELLS
in the mucosa of the lower duodenum and jejunum sense: lipids and partially digested proteins, the low pH of chime entering the intestine
Gut endocrine cells secrete 2 small peptide hormones to blood?
cholecystokinin (CKK) and secretin
a small peptide hormone secreted to the blood in response to the presence of lipids and partially digested proteins
CCK does what?
promotes pancreatic enzyme secretion, causes gallbladder to release bile, decreases gastric motility, reducing release rate of gastric contents to the small intestine
bile salts, phospholipids, free cholesterol
a small peptide hormone secreted to the blood in response to the low pH of chime entering the intestine
What does secretin do?
promotes the release of bicarbonate rich solution from the pancreas to the small intestine, providing the appropriate pH for optimal pancreatic enzyme function
Absorption of lipids by intestinal mucosal cells
What are the three primary products of lipid digestion in the in the jejunum?
free fatyy acids, free cholesterol, 2-monogacylglycerol
disk shaped clusters of amphipathic lipids/ are formed from these three products, bile salts and fat-soluble vitamins (A,D,E,K)
Enterocytes components coalesce/arrange such that their hydrophobic groups are....and their hydrophilic groups are....to the aqueous solution
Mixed micelles are soluble in the... and can approach and associated with the brush border membrane of enterocytes (intestinal mucosal cells) where they are absorbed
....relative to there dietary lipids are poorly absorbed by enterocytes
What kind of fatty acids can be absorbed directly without mixed micelles?
short and medium fatty acids
The absorbed mixture of lipids is processed at the ...., the site for complex lipid biosynthesis
Fatty acyl-CoA synthetase
need to be able to recognize - can add fatty acids to a co-A molecule
What are the components of a chylomicron?
Tracylglycerol, Apolipoprotein B-48, Phospholipids, and Cholesteryl ester
FATTY ACYL - COA SYNTHETASE (THIOKINASE)
converts long chain fatty acids to their activated form by using energy from ATP -> AMP to form fatty acyl CoA
2-monoacylglycerol is converted to TAG by an enzyme complex that sequentially adds activated fatty acids (above) by the two enzymatic acyltransferase activities
acyl CoA: cholesterol acyltransferase
esterifies cholesterol with a fatty acid
Lyspholipids are re-acyltated by a family of specific acyltransferases to form..
phospholipids (most are secreted and this is unnecessary)
What is not activated by released into the portal circulation and likely carried by serum albumin to the liver?
short and medium fatty acid chains
TAG and cholesteryl esters are.... and thus need to be packaged into stable lipid droplets, called chylomicrons, to be secreted by the intestinal enerocytes
Composition of chylomicrons
TAG and cholesteryl esters - surrounded by a spherical single layer of phospholipids, cholesterol and Apolipoprotein B-48
produced at the ER of the enterocytes, exocytosed into the lacteals (lymphatic vessels that originate at the vili of the small intestine)
What is lymph that contains chylomicrons?
Chyle passes via.....to the thoracic duct, from the thoracic duct to the left subclavian vein, and then enters the blood
enzymatically degrades TAG in the circulating chylomicrons to free fatty acids and glycerol
Where is Lipoprotein lipase synthesized and secreted?
primary by muscle and adipose tissue (also heart, lung, kidney, and liver)
What is Lipoprotein lipase associated with?
lumen endothelial cells of capillary beds
The free fatty acid are generally take up immediately by the adjacent muscle and adipose tissue, but if not, the....will circulate in association with serum albumin if not taken up
free fatty acids
Glycerol is taken up by the liver and used to produce...which can enter glycolysis or gluconeogenesis
The remaining components of the chylomicron interact with receptors on the livers cells and are..
What are the remaining components of the chylomicron?
phospholipids, cholesteryl esters, apoliproteins, fat-soluble vitamins and remaining TAG
Most of the materials are hydrolyzed to their component parts but..... and.... are recycled
nitrogenous bases and phospholipids
increased excretion of essential dietary lipids (including fat-soluble vitamins and essential fatty acids) in the feces caused by lipid digestion and absorption problems
Causes of lipid malabsorption
can be related to CF (poor digestion) or shortened bowl (decreased absorption)
is an autosomal recessive disease with varying degrees of severity and multiple alleles
Cystic fibrosis - the mutations affect a.....ion channel CFTR that is important for the hydration and thus viscosity of mucus
With relevance to the lipid digestion, the reduce function of CFTR in the secretory ducts of the pancreas results in...
thick viscous mucus that blocks the secretion of pancreatic enzymes (critical for lipid digestion) to the small intestine
results in a significant reduction in dietary calories and decreased fat soluble vitamin up-take
Depending on the severity of the disease (pancreatic insufficiency), this results in...
delayed growth and energy deficiency especially noticeable in children
Treatment of CF
includes enzyme replacement and fat-soluble vitamin supplements
Sets with similar terms
Digestion and Absorption II - Lipids and Role of B…
Small intestine - digestion and absorption
Chapter 5 Lipids
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