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