lecture 4: lipid digestion & absorption

Question 1

4 major roles of lipids in the body

Answer 1

fuel for energy, structural component of cellular membranes, lubricants, signaling molecules

Question 2

acylglycerols

Answer 2

major lipid class of the body
concentrated form of energy
tryacylglycerol (TAG) critical in metabolism, primary storage of fat

Question 3

why is fat the preferred storage form of energy?

Answer 3

more energy per gram
they do not associate with water, less weight (carbs have hydrophilic interactions)

Question 4

high dietary carbs >

Answer 4

liver synthesizes FA

Question 5

fatty acid and triacylglycerol metabolism

Answer 5

series of hydrolysis and re-esterification reactions
FA transported across membranes
TAG = major form of lipids in lipoproteins in circulation

Question 6

resting muscles primarily use what for energy?

Answer 6

glucose

Question 7

working muscle….

Answer 7

oxidizes fatty acids at higher levels

Question 8

gastric lipase

Answer 8

secreted in stomach, active in acidic environment
hydrolyzes FA at sn3 position

TAG > DAG + FA

Question 9

fatty acids stimulate the release of

Answer 9

CCK in the blood > contractions in gallbladder > bile release

Question 10

bile acids

Answer 10

in bile, interact with surface of lipid droplets and act as emulsifiers

Question 11

pancreatic lipase

Answer 11

digest most TAG in small intestine
works at the aqueous-lipid interface of emulsified lipid particles
TAG > MAG + 2FA

Question 12

colipase

Answer 12

activated by trypsin
binds to aqueous-lipid interface, facilitates binding and anchoring of pancreatic lipase (otherwise inhibited by bile acids)

Question 13

phospholipase A2

Answer 13

digests phospholipids, hydrolyzes sn2 position

Question 14

carboxyester lipase

Answer 14

excreted by pancreas in active form, products free cholesterol and FA products

acts on substrates in aq-lipid interface of micelles, stimulated by bile acids

Question 15

micellar solubilization

Answer 15

essential to absorption of hydrophobic products
enables products of digestion to cross barrier presented by water layer surrounding enterocytes

Question 16

the concentration gradient between apical membrane and intracellular compartment favors…

Answer 16

initial diffusion of products into the cell
digestion products rapidly re-esterified > maintain low intracellular conc > continued lipid uptake

Question 17

fatty acid translocase CD36

Answer 17

translocates long-chain fatty acids across apical membrane of enterocyte
carrier for uptake of FAs

Question 18

transport protein NPC1L1

Answer 18

major role in absorption of cholesterol

Question 19

how are absorbed FAs transported?

Answer 19

most are incorporated into TAGS and transported through lymph in chylomicrons

others are transported to liver through portal vein

Question 20

portal transport of FAs

Answer 20

most FAs are incorporated in TAG, transported through lymph as chylomicrons

transport to liver by portal vein is the preferential transport by medium chain FAs
double bonds in long chain FAs increase rate of transport

Question 21

neurotensin

Answer 21

intestinal peptide hormone that enhances lymphatic lipid transport

Question 22

glucagon-like peptide 2 GLP2

Answer 22

increases lipid absorption and chylomicron secretion
released in response to fat/carb consumption

Question 23

outlined process of carrier-mediated uptake of FAs

Answer 23

CD36 translocates FA
FABP transports FA to ER
FAs metabolized by FABP and ACSL
ACAT, MGAT, DGAT are ER membrane proteins and facilitate esterification of cholesterol