Lipid Transport

Chylomicrons are assembled in the intestine, what do they go through before becoming chylomicron remnants

Enter the lymphatic system and deliver TAGs to tissues

VLDL circulates to peripheral tissues and becomes IDL, from there it either

Taken up by hepatic LDL-R or further hydrolyzed to LDL

Reverse cholesterol transport

HDL carries cholesterol to the liver or CETP mediates transfer of CEs to lDL

Cholesterol is eliminated from the body by

Conversion to bile acids or secretion as is

LDL delivers cholesterol for essential functions BUT

Can also deposit cholesterol in unwanted places

What do higher HDL levels mean

More cholesterol returning to the liver

Lipid metabolism in liver following a meal: Glucose comes in from what vein in the GI

Portal vein

Lipid metabolism in liver following a meal: In what form do chylomicrons arrive at the liver

Chylomicron remnants after having entered the lymphatic system, travelled all around the body and lost a lot of TAGs

Lipid metabolism in liver following a meal: What does glucose become and why

Glucose-6-phosphate for glycogen production, glycolysis, hexose monphosphate shunt

Lipid metabolism in liver following a meal: What is de novo lipogenesis - carbs can be used to synthesize fatty acids!

G6P goes to glycolysis to become Acetyl-CoA and make fatty acids

Lipid metabolism in liver following a meal: Fatty acids can’t sit around since they are toxic, where are they sent

Triglyceride pool

Lipid metabolism in liver following a meal: Where is the triglyceride pool sent

To VLDL and HDL to go to adipose for long term storage

Lipid metabolism in liver following a meal: Amino acids come from proteins, what can they be converted to

Oxaloacetate/pyruvate to help with triglyceride function

Lipid metabolism in the adipose cell following a meal: ApoC in chylomicrons activates

LPL

Lipid metabolism in the adipose cell following a meal: What does LPL do once activated

Breaks down TAGs to become glycerol and fatty acids to cross membrane

Lipid metabolism in the adipose cell following a meal: Fatty acids enter the pool, what helps support the Fatty acid and TAG pools

FFA, DG, MG

Lipid metabolism in the adipose cell following a meal: Glucose goes to G6P then Acetyl-CoA, what are minor and major end points

Minor: Kreb’s

Major: Fatty acid pool

How do lipids fit into gluconeogenesis

Glycerol backbone is glucogenic

How do lipids fit into Kreb’s

Fat oxidation via Acetyl CoA

Gluconeogenesis from lipids: What hydrolyzes ester linkages to remove fatty acids from glycerol backbone

Lipase

Gluconeogenesis from lipids: What does HSL (hormone sensitive lipase) do for glycerol backbone

Cleave fatty acids from glycerol backbone

Gluconeogenesis from lipids: What inhibits HSL

Insulin

Gluconeogenesis from lipids: Why does insulin inhibit HSL

Insulin increases after a meal, feedback to inhibit HSL and lipolysis since we are getting energy from food

Gluconeogenesis from lipids: Insulin decreases during fasting, then what

HSL goes up to tap into stores

Gluconeogenesis from lipids: What can glycerol enter after being freed from fatty acids

Glycolysis for ATP or gluconeogenesis

Gluconeogenesis from lipids: What can fatty acids undergo to generate energy

Beta oxidation

Each round of B-ox removes what and produces what

Removes 2 carbons, produces 1 NADH and 1 FADH2 for the ETC

Relationship between rounds of B-ox and number of carbons

n/2 - 1

How many ATP is Acetyl-CoA, NADH, FADH2 equivalent to

Acetyl-CoA = 12 ATP

NADH = 3 ATP

FADH2 = 2 ATP

Does the body make all the cholesterol we need

Yes, anything from the diet is extra

What should people with high cholesterol do to lower LDL (transport of cholesterol from liver to body)

Less dietary cholesterol

How do plant sterols lower cholesterol absorption at the gut

Compete with cholesterol for uptake into the enterocyte

What apical protein takes cholesterol/plant sterols

NPC1L1

Once in the intestinal cells, what is the fate of cholesterol and what is the fate of plant sterols

Cholesterol incorporated into chylomicrons, plant sterol is filtered back out to lumen - PLANT STEROLS ARE TAKEN UP BY ENTEROCYTES BUT NEVER ABSORBED INTO BLOOD

What transporters pump plant sterols back into the lumen

ABCG5 and ABCG8

Are there health concerns for natural fatty acids

No, only industrial ones that are produced to increase food stability

What is partial hydrogenation of trans fatty acids

Double bonds get converted from cis to trans

What is complete hydrogenation of trans fatty acids

All double bonds are fully saturated, increase hydrogenation increases degree of saturation

Where are Trans fats found naturally

In rumen fat, made through bacterial fermentation

What increases the risk of CVD more than any other nutrient

Trans fats, increase LDL, increase cholesterol, increase inflammation, lower HDL

Outcome of monounsaturated/mediterranean diet

Lower CVD risk, lower risk for metabolic syndrome, lower risk for certain cancers

Outcome of polyunsaturated/fish, fish oil diet

Lower risk for CVD, lower risk for arthritis, reduce inflammation