32. Integration of Whole Body Metabolism

Question 1

Describe the brain? (6pts)

Answer 1

1. The brain uses glucose as its primary source of energy
2. Over half the energy consumed is used for sodium and potassium transport to maintain membrane potential and the synthesis of neurotransmitters.
3. Lacks energy stores
4. Glucose is transported by GIUT3 which has a low km
5. Danger point when plasma glucose drops to below 2.2 mM
6. Normally fatty acids are used for membrane biosynthesis.

Question 2

Describe cardiac muscle? (2pts)

Answer 2

1.Exclusively aerobic with little or no glycogen stores 2.Fatty acids are the main source of energy followed by lactate and ketone bodies.

Question 3

Describe Adipose tissue? (3pts)

Answer 3

1. Act as a metabolic reserve of energy in the form of triglycerides
2. Triglycerides come from the diet and are delivered by chylomicrons. They are synthesised by the liver and transported via the VLDL.
3. Glucose is transported by GLUT4 which is insulin sensitive.

Question 4

Describe the kindey? (5pts)

Answer 4

1. Major role is to produce urine
2. The plasma is filtered up 60 times daily
3. Only a small volume of urine is produced.
4. Water soluble material largely reabsorbed to prevent loss
5. During starvation the kidney may contribute half of the blood glucose through glucogenisis.

Question 5

Describe the liver? (4pts)

Answer 5

1. Play a central role in regulating metabolism off carbohydrates, fatty acids and amino acids.
2. Most compounds absorbed by the gut pass through the liver.
3. Provide fuel for the brain, muscle and other peripheral organs.
4. Takes its energy from a-ketoacids.

Question 6

Describe the control of blood glucose by liver metabolism? (2pts)

Answer 6

1. Glucose is transported into hepatocytes by Glut-2 and immediately phosphorylated by glucokinase.
2. Glucose-6-phosphate is converted to glucose via glucose-6-phosphatase and transported out of the cell and into the blood by Glut-2.

Question 7

Describe muscle glucose metabolism? (5pts)

Answer 7

1. Glucose uptake by Glut-4 is insulin-dependant.
2. Glucose is converted into G6P by hexokinase
3. Low free glucose is in the cell
4. Glucose is mobilised from glycogen in exercise.
5. Glycolysis of G6P is a rapid source of ATP.

Question 8

When is Glucokinase activated?

Answer 8

Glucokinase is activated only in circulating glucose concentrations

Question 9

How is fuel for a sprint generated? (7pts)

Answer 9

1. Requires rapid mobilisation of energy stores
2. ATP directly powers muscle contraction
3. Power and speed is dependent on the availability of ATP.
4. Muscle ATP stores are small
5. Largely anaerobic
6. ATP is generated via:
7. ATP stores
8. Glycolysis
9. Glycogenolyiss
10. Creatine Phosphate
11. The build up of lactate and the fall in PH ultimately limits performance.

Question 10

Describe how creatine phosphate generates ATP?

Answer 10

Creatine phopshate + ADP= ATP+ Creatine

• small but rapidly mobilized ATP store lasting only a few seconds

Question 11

Describe how fuel for a marathon is generated? (7pts)

Answer 11

1. Requires sustained energy provision
2. Uses aerobic respiration as it is more efficient
3. Requires co-operation of the muscle, liver and adipose tissue
4. Initially glycogen is used but later fat is mobilised from the adipose tissue.
5. Fats are a large source of ATP but metabolism is x10 slower than creatine phosphate.
6. The combined use of both glycogen and fats is more efficient
7. The result is approximately half of the glycogen stores remain.

Question 12

What happens during extreme excercise? (2pts)

Answer 12

1. During extreme exercise protein degradation occurs producing alanine via transaminase reactions.
2. Alanine is transported to the liver where it is converted too glucose.

Question 13

What happens when we stop eating?

Answer 13

1. The first priority is to maintain glucose levels
2. The second priority is to preserve protein
3. To achieve this metabolism shifts from glucose to fatty acids and ketone bodies.

Question 14

Describe the post absorptive phase- period after fasting? (3pts)

Answer 14

1. Blood glucose falls, insulin levels fall and glucagon levels rise
2. Phosphorylase activity increases as does glycogen breakdown
3. The drop in insulin reduced glucose uptake by muscle and adipose tissue.

Question 15

Describe what happens in early starvation (24hrs)?

Answer 15

1. Glucose is released from the liver due to glycogensis and glycogenolysis.
2. Mobilisation of fatty acids from adipose tissue occurs.
3. Glucose use falls as muscle switches to fatty acid oxidation.
4. Insulin drops causing GLUT4 expression by muscle to fall reducing glucose uptake.
5. After 12 hours 45% resting energy from fatty acids and 45% resting energy from glucose is used
6. Initial increase in protein breakdown occurs.

Question 16

What happens during intermediate starvation (3-20 days)? (7pts)

Answer 16

1. Glycogen stores are depleted
2. Increased lipolysis and ketogenesis
3. Increased glycogenesis to maintain blood glucose
4. 60 hrs fatty acid account for 3/4 energy provision
5. After 8 days B-hydroxybutrate is raised 50 fold
6. Further starvation sees the kidney take over glycogenesis from the liver.
7. Ketone bodies increase

Question 17

Describe what happens during prolonged starvation? (6pts)

Answer 17

1. B-hydroxybutrate plateaux at 20 days
2. Brain starts to use ketone bodies instead of glucose as its primary energy source and the need for glucose falls from 100g to 40g.
3. Other sources of glycogenic precursors are lactaste and glycerol
4. Lactate is recycled by the Cori cycle
5. Glyerol and amino acids are oxidised
6. Proteins are broken down by the muscle forming amino acid precursors.