Feed-Fast Cycle

Question 1

When is absorptive/well-fed state?

Answer 1

First bite of food -> 2-4 hr after ingestion of meal

Question 2

When is fasting state?

Answer 2

4 hours after meal

Question 3

What is increased in fed state?

Answer 3

• Plasma glucose, AAs and TAG

- Pancreas: insulin (decreased glucagon)

Question 4

Why is fed state an anabolic period?

Answer 4

Increased TAG/gylcogen, replenish fuel stores, enhanced protein synthesis

Question 5

Who uses glucose as fuel?

Answer 5

All tissues

Question 6

What changes happen in enzymes during fed state?

Answer 6

1) Substrate availability (very quick)
2) Allosteric changes (very quick)
3) Kinases addition, phosphatases removal of phosphate groups (minutes -> hours)
4) Gene level - induction/repression enzyme synthesis (takes hours -> days)

Question 7

In your liver during fed, what is the first thing that will happen?

Answer 7

Glycogenesis

Question 8

How does glucose enter the liver? Is it insulin dependent/independent?

Answer 8

GLUT-2 (insulin-INDEPENDENT)

-Just reacts to the fact that blood [glucose] increased because you just ate

Question 9

What happens to the excess glucose?

Answer 9

AAs from gut -> liver -> fat (VLDLs)

• AAs also make proteins
• some AAs make acetyl CoA -> TCA cycle
• some made pyruvate -> glycogenesis
• excess will make urea

Question 10

2 key outcomes of liver in fed state?

Answer 10

Glycogen and fat

Question 11

What plays a central role in sugar metabolism?

Answer 11

G6P

Question 12

Upregulation by GLUT-4 mediated by insulin occurs only where?

Answer 12

Muscle and adipose only

Question 13

Upregulation by GLUT-4 mediated by glucagon occurs only where?

Answer 13

No where

-Glucagon will never regulate uptake of glucose

Question 14

Making of ketone bodies, most significance portion of gluconeogenesis during fasting, breaking down glycogen to maintain normal blood [glucose], manage making urea when AA is being broken down.. occurs where?

Answer 14

Liver only

Question 15

I activate HSL during fasting.

Answer 15

Adipose only

Question 16

If I don’t uptake glucose, I will die.

Answer 16

RBCs only

Question 17

When I break down glycogen I use that glucose in TCA cycle.

Answer 17

Liver only

Question 18

What happens in adipose tissue during fed?

Answer 18

1) Glucose comes in via GLUT-4
2) Glucose -> G6P -> pyruvate -> acetyl CoA -> TCA cycle
3) Making of TAG from glycerol + FAs (released from chylomicrons and VLDLS)

Question 19

When insulin goes down at 3 am what will happen in your muscle cells?

Answer 19

Breakdown of protein (especially alanine)

Question 20

In fed state what happens in resting skeletal muscle?

Answer 20

1) Glucose comes in via GLUT-4
2) Glycogenesis
3) TCA cycle
4) AAs -> Protein

Question 21

What happens in the brain in fed?

Answer 21

Same as in fasting because loves glucose so much:

1) Glucose comes in via GLUT-1 (insulin insensitive) -> TCA cycle

Question 22

When does brain stop using glucose?

Answer 22

After 3 days of starvation

Question 23

What happens to plasma levels in fasting?

Answer 23

Gluocse, AAs and TAG decrease

-Insulin secretion decreases, glucagon/ephinephrine increases

Question 24

Why happens in catabolic (fasting) period?

Answer 24

1) Glycogen degradation in liver
2) TAG degradation (fat cells activate HSL -> FAs -> liver, muscle + glycerol -> only liver for gluconeogenesis)
3) Protein degradation

Question 25

What are 2 priorities during fasting?

Answer 25

1) Maintain adequate glucose (for RBCs + brain) | 2) Mobilize FAs from adipose (liver use them for energy + make KBs)

Question 26

What supplies the great majority of energy stores?

Answer 26

TAG | -Glycogen is very minimal compared to what you get from FAs

Question 27

What happens 1st to the liver during fasting?

Answer 27

Glycogenolysis

Question 28

What happens 2nd to the liver during fasting?

Answer 28

Gluconeogenesis | -Takes longer and more energy

Question 29

At 3 day mark (starvation) what is shut down?

Answer 29

Gluconeogenesis | -B/c comes tremendously from muscle protein

Question 30

What is the enzyme present in the liver that will break down G-6-P to free glucose?

Answer 30

Glucose 6-phosphatase

Question 31

In fasting, where are the free FAs coming from in the liver?

Answer 31

Adipose carried on albumin | -Not TAG/chylomicrons/VLDLs (like in fed)

Question 32

During fasting, what is used by the liver for ketogenesis?

Answer 32

AAs, lactate + glycerol (from muscle and adipose) -> beta-oxidation

Question 33

What is the liver not able to do with the KBs?

Answer 33

Use them | -lacks thiophorase enzyme

Question 34

What favors gluconeogenesis in the liver?

Answer 34

Pyruvate -> activation of fructose 2,6-bisphosphatase

Question 35

Can the brain use KBs?

Answer 35

Yes when concentrations are really high | -after 3 days 3-hydroxybutyrate (KB) extremely increases

Question 36

What is the 1st enzyme/process in adipose tissue during fasting?

Answer 36

Lipolysis by HSL

Question 37

What is the 2nd process in adipose tissue during fasting?

Answer 37

Release of 3 FAs + glycerol into blood

Question 38

How does the muscle know that you are fasting?

Answer 38

Very sensitive to low insulin | -Does not know there is high glucagon (no glucagon receptors)

Question 39

What does the muscle 1st do during fasting?

Answer 39

Break down its protein -> AAs -> gluconeogenic precursors (glutamine + alanine -> liver)

Question 40

What does the muscle use during fasting to meet energy needs?

Answer 40

FAs and KBs

Question 41

After 3 days of starvation what does muscle stop using?

Answer 41

KBs | -Brain needs them