Integration of Metabolism

Question 1

What is the body’s primary energy store?

Answer 1

TAGs in Adipose Tissue

Question 2

Why are proteins used as fuel during the fed state?

Answer 2

Normal Protein Turnover is happening, as old proteins are degraded their amino acids are recycled

Question 3

Even when you are staving glycogen still sits in the muscle untouched. How is this glycogen maintained while liver glycogen is broken down?

Answer 3

• Muscle glycogen is only responsive to epinephrine, not glucagon
• High Levels of Glucagon indicating absence of glucose doesn’t affect glycogen breakdown enzymes
• These glycogen stores will be present as long as you don’t have to sprint or release epinephrine for some other reason

Question 4

How does the brain save muscle from breaking down?

Answer 4

• Gluconeogenesis starts at about 12 hrs no food and ceases for the most part after around 3 days
• from 12-72 hours this process is largely running off of protein breakdown products which come from the muscle
• After 72hrs the brain starts to run on ketone bodies and the only thing left that needs to use gluconeogensis are RBCs.

Question 5

What is the main fuel source for the brain?

Answer 5

• Glucose

- Ketone Bodies ( after 3d)

Question 6

What are they only organs in the body that can export molecules that can be processed and used for energy?
-What are the exports?

Answer 6

1. Skeletal muscle:
   - Lactate (ONLY DURING HARD EXCERCISE)
   - Amino Acids (only during fasting)
2. Adipose tissue - FA and glycerol
3. Liver - TAGs, Glucose, Ketones

Question 7

What tissues prefer to use fatty acids in their resting states?

Answer 7

Skeletal muscle, Cardiac muscle, Adipose tissue, Liver

Note: this does not refer to fed state in which everything prefers glucose

Question 8

What are the major substrates for gluconeogenesis?

-Where do these come from?

Answer 8

1. Lactate - remaking NAD+ (lact. dehydr.)
2. Alanine - protein breakdown
3. Glycerol - LPL or Hormone Sensitive Lipase

Question 9

What enzyme is required to enter glycerol to gluconeogenesis?

Answer 9

Glycerol Kinase

Question 10

Why are fatty acids not used for gluconeogenesis?

Answer 10

• Because there is no net gains of carbons during the TCA cycle (none are available for biosynth)
• AcCoA cannot be turned to FAs

Question 11

What substrates are required to make fats?

Answer 11

Acetyl CoA, Glucose, Glycerol

Question 12

What starting material is needed for the PPP?

Answer 12

Glc-6-P

Question 13

When is all glucose depleted by fed state?

Answer 13

~2hrs at this point you enter the post-prandial state

Question 14

When does the postabsorptive state begin and end, what processes are supplying the body with energy?

Answer 14

~6-8 hours (ends after 12 hrs)

- Glycogenolysis from the liver keeps the body supplied

Question 15

When does the Basal state begin and end, what processes are supplying the body with energy?

Answer 15

~12 hrs (ends after 24hrs)

• Gluconeogensis - Brain, RBCs
• Ketone body Synth - skeletal muscle

Question 16

In what state will Chylomicrons and VLDLs be broken down?

Answer 16

Fed state only

- In any other state chylomicrons and VLDLs have already been been extracted by fat cells

Question 17

What is the endogenous fat transporting particle?

Answer 17

-VLDLs

Question 18

When would you expect urea levels to be the highest and why?

Answer 18

• Urea will be the highest in the basal and fasting state when gluconeogenesis is still ramped up
• High urea results from lots of proteins being broken down.
• In times before and after this (fed and starving states) there is relatively little protein breakdown

Question 19

What is the cori cycle?

Answer 19

• Uses lactate to remake glucose for the RBCs

Question 20

You find a camper that has been lost for 5 days, you feed him 3 packs of ramen noodles and he dies. Why did he die?

Answer 20

• His body is not used to using glucose, a high fat meal would have been a better choice

Why:

• GLUT2 is hardly expressed at all so liver and pancreas don’t even realize there is glucose in the body
• Most glucose will bypass the kidney and get taken up by muscle since it has GLUT1
• Muscle glycolysis overloads TCA and pyruvate gets converted to lactate which can be converted to more glucose because GLUCONEOGENESIS enzymes are high
• Ultimately the lactate builds up and the guy dies from lactic acidosis.

Question 21

When is the only time the body is using exogenous glucose?

Answer 21

• Fed state (~0-4 hrs)

Question 22

What state is defined as glycogenolysis being greater energy contributor than gluconeogenesis?

Answer 22

Post-absorptive state (between fed and basal states)

Question 23

In what state would you expect lactate levels to be the highest?

Answer 23

During the Fed State

Question 24

What hormone is responsible for maintaining blood glucose levels during fasting?

Answer 24

Glucagon

Question 25

What hormone is responsible for fatty acid mobilization?

Answer 25

Glucagon

Question 26

T or F: glucagon has an effect on protein synthesis?

Answer 26

False

Question 27

What is the only other tissue glucagon can communicate with besides the liver?

Answer 27

• Can increase lipolysis in Adipose Tissue

Question 28

Where is the glucose-6-phosphatase reaction found?

Answer 28

Endoplasmic Reticulum

Question 29

T or F: after 2 days in the woods your brain would be using mostly muscle protein to as its primary fuel source.

Answer 29

True - glucneogenesis is running and the starvation state of conserving proteins and using ketone bodies in the brain has not yet kicked in.

Question 30

After 2 days what would be the fuel sources for the brain?

Answer 30

- Glucose is the fuel
Sources:
-Lactate - from CORI cycle
-Alanine - from alanine cycle
- Glyercol (TAGs) - only a small amount

Question 31

What fuel source do you use if you haven’t eaten for 10 days and you sprint away from a lion?

Answer 31

• Glycogen - muscle glycogen is not used during starvation because it doesn’t recognize glucagon, only epinephrine which would be stimulated when running from the lion