Ch. 5 "The Lipids" - 5.3 "Digestion, Absorption, & Transport of Lipids"
Lipoproteins made by the liver that transport lipids (primarily triglycerides) from the liver to other tissues
VLDL
Which type of lipoprotein?: Smaller than chylomicrons & contain about 50% triglycerides
VLDL
Most of the bile released into the small intestine is reabsorbed & sent back to the liver to be reused. This cycle is called the:
enterohepatic circulation of bile.
When fat enters the small intestine, it triggers the release of the hormone CCK, which signals the ___ to release its stores of ___.
gallbladder; bile
Small molecules can diffuse easily into the intestinal cells; they are absorbed directly into the bloodstream. Name these small molecules.
glycerol & short- & medium-chain fatty acids
Which fat molecules can move directly into the bloodstream during diffusion in the intestinal cells?
glycerol & small lipids, such as short- & medium-chain fatty acids
Phospholipid fatty acids are removed by ___.
hydrolysis
Are digestive enzymes hydrophilic or hydrophobic?
hydrophilic
Are lipids hydrophilic or hydrophobic?
hydrophobic
Compare the salivary gland enzyme lingual lipase action in infants vs. adults.
infants: active role in digesting short & med. chain fatty acids found in milk; adults: relatively minor role in fat digestion
The ___ carefully regulate the production and release of the chylomicrons into the lymphatic system
intestinal cells
What does bile do in the stomach for fat digestion?
it emulsifies fats (mixes w. pancreatic & intestinal lipases, the digestive enzymes for fats)
Which fat molecules must combine w. bile & form micelles that are sufficiently water-soluble to penetrate the watery solution that bathes the absorptive cells of the small intestine?
large lipids such as monoglycerides & long-chain fatty acids
Simply put, what's a micelle?
large lipids that have combined w. bile so that they lipids are water-soluble & can diffuse into the intestinal cells
Each type of lipoprotein contains different kinds & amounts of lipids and proteins. The more lipids, the (less/more) dense; the more proteins, the (less/more) dense.
less; more
Keep in mind that the cholesterol itself in LDL & HDL is the same & that the differences between LDL & HDL reflect the proportions & types of ___ & ___ w.in them—not the type of cholesterol.
lipids; proteins
Where is bile made?
liver
Where is the most active site of lipid synthesis?
liver
Describe how bile is both hydrophilic & hydrophobic.
the amino acid end bile pairs up w. is hydrophilic; the sterol end (b.c. bile's made from cholesterol) is hydrophobic
T/F: Bile is a digestive enzyme.
F; Bile isn't a digestive enzyme; but it is essential in preparing fats for digestion by the lipase enzymes from the pancreas & small intestine.
A fat-digesting enzyme secreted from the cells of the stomach
Gastric Lipase
Which type of lipoprotein?: The densest & rich in protein
HDL
Lipoproteins that derive from VLDL and transport lipids (primarily cholesterol) in the blood
LDL
Which lipoprotein?: Linked most directly to heart disease.
LDL
Pertaining to the tongue
Lingual
A fat-digesting enzymes secreted from the salivary gland at the base of the tongue
Lingual Lipase
Enzymes that hydrolyze lipids
Lipases
Clusters of lipids associated with proteins that serve as transport vehicles for lipids in the lymph and blood
Lipoproteins
Tiny spherical complexes of emulsified fat that arise during digestion; Fat that arise during digestion; Most contain bile salts & the products of lipid digestion, including fatty acids, monoglycerides, cholesterol
Micelles
Molecules of glycerol w. 1 fatty acid attached
Monoglycerides
Emulsified Fat (Triglycerides) > Pancreatic (& Intestinal) Lipase > ___
Monoglycerides, Glycerol, Fatty Acids (Absorbed)
After bile enters the small intestine & emulsifies fat, it has 2 possible destinations. What are they?
Most bile is reabsorbed from sm. intestine & recycled; Some of the bile can be trapped by dietary fibers in the large intestine & excreted.
How are sterols absorbed?
Most sterols can be absorbed as is; if any fatty acids are attached, they're 1st hydrolyzed off.
How many milligrams of cholesterol does the GI tract receive each day from the food we eat?
200-350 milligrams
How many different types of lipoproteins does the body make?
4
How many grams of phospholipids does the GI tract receive each day from the food we eat?
4-8 grams
How many grams of triglyceride does the GI tract receive each day from the food we eat?
50-100 grams
Describe the pancreas's role in fat digestion.
After CKK has signaled the gallbladder to release bile & the fat & enzymes have been emulsified by bile, pancreatic lipase flows in from the pancreas via the pancreatic duct
Describe the excretion of bile's effect of blood cholesterol.
B.c. cholesterol is needed to make bile, the excretion of bile effectively reduces blood cholesterol; Thus, fibers that trap bile are effective at reducing blood cholesterol.
A digestive secretion that is made by the liver, stored in the gallbladder, & released into the small intestine when needed (namely, when fat enters the small intestine)
Bile
One of bile's many ingredients, which are made in the liver from cholesterol & have a similar structure
Bile Salts
Lipoproteins that transport lipids from the intestinal cells to the rest of the body
Chylomicrons
A molecule of glycerol w. 2 fatty acids attached
Diglyceride
What's the ultimate goal of fat digestion?
Dismantle triglycerides into sm. molecules the body can absorb & use (namely, monoglycerides, fatty acids, glycerol)
Fat > Bile > ___
Emulsified Fat
T/F: High LDL & low HDL cholesterol are both associated with a high risk of heart disease.
T
At what point to the chylomicrons enter the bloodstream?
The chylomicrons glide through the lymph until they reach a point of entry into the bloodstream at the THORACIC DUCT near the heart.
Describe the end-product of hydrolysis of a triglyceride by the fat-digesting enzyme pancreatic lipase (as well as some intestinal lipase).
The enzymes remove ea. of a triglyceride's fatty acids 1 at a time, leaving a monoglyceride; sometimes they remove all 3 fatty acids, leaving a free molecule of glycerol.
What purpose does that liver have for making HDL?
The liver makes HDL (high-density lipoproteins) to remove cholesterol from the cells & carry it back to the liver for recycling or disposal.
What is it that bile often pairs up w. that makes 1 end of bile hydrophilic?
an amino acid
If HDL carries cholesterol, why is it not implicated w. heart disease?
b.c. the cholesterol it carries represents cholesterol returning from the rest of the body to the liver for breakdown & excretion
When fat enters the small intestine, it triggers the release of the hormone ___.
cholecystokinin (CCK)
Name the hormone that signals the gallbladder to release bile.
cholecystokinin (CKK)
W.in the intestinal cells, the newly made triglycerides and other lipids (cholesterol & phospholipids) are packaged w. proteins to make transport vehicles known as ___.
chylomicrons
Which lipoprotein?: Cells all over the body remove triglycerides from the them as they pass by, so they get smaller and smaller.
chylomicrons
Which lipoprotein?: The largest
chylomicrons
Which lipoprotein?: The least dense
chylomicrons
Which lipoprotein?: They transport diet-derived lipids (mostly triglycerides) from the small intestine (via the lymph system) to the rest of the body
chylomicrons
Name the 4 different types of lipoproteins.
chylomicrons; very-low-density lipoproteins (VLDL); low-density lipoproteins (LDL); high-density lipoproteins (HDL)
Benefits of HDL:
clears cholesterol; removes plaque buildup; lowers risk of heart disease; have anti-inflammatory properties that seem to keep plaque from breaking apart & causing heart attacks
The intestinal cells carefully regulate the production and release of the chylomicrons into the ___.
lymphatic system
Larger molecules are emulsified by bile before being diffused into the intestinal cells. Name these large molecules.
monoglycerides & long-chain fatty acids
The goal of fat digestion is to dismantle triglycerides into small molecules that the body can absorb & use. Name the molecules they triglycerides are to dismantled into.
monoglycerides, fatty acids, glycerol
What are the end products of fat digestion?
mostly monoglycerides; some fatty acids; very little glycerol
Name major fat-digesting enzyme(s).
pancreatic lipases; some intestinal lipases are also active
The transport of cholesterol from the tissues back to the liver is sometimes called ___ or ___.
reverse cholesterol transport; scavenger pathway
Lipoproteins are distinguished by their ___ & ___.
size; density
Most of the hydrolysis of triglycerides occurs in the ___.
small intestine
Where does most fat digestion occur?
small intestine
List some of the dietary fibers most effective at lowering blood cholesterol.
soluble fibers commonly found in fruits, whole grains, legumes
Describe the large intestine's role in fat digestion.
some fat & cholesterol (trapped in fiber) exit in feces
Describe fat digestion in the mouth.
some hard fats melt; lingual lipase secreted but the hydrolysis is slight for most fats (may be appreciable for milk fats)
Describe fat digestion in the stomach.
stomach's churning mixes fat w. water & acid; gastric lipase accesses & hydrolyzes (only a v. sm. amt.) of fat
The blood, fat stores, & muscle cells of people who eat a diet rich in unsaturated fats contain more ___ than those of people who select a diet high in saturated fats.
unsaturated fats
List some factors help lower LDL &/or raise HDL.
weight control; MUFAs or PUFAs instead of sat fat in diet; soluble dietary fibers; phytochemicals; moderate (or no) alcohol consumption; physical activity