Integration of whole body metabolism

Question 1

How much energy does the brain use and what is it used for

Answer 1

• Uses 100-120g of glucose daily
• Over half of the energy used is for Na+ K+ transport to maintain membrane potential and the synthesis of neurotransmitters

Question 2

How is glucose transported in the brain

Answer 2

GLUT3, which has a low Km therefore is saturated at low glucose concentrations

Question 3

Why aren’t fatty acids used for energy

Answer 3

Since they are used membrane biosynthesis

Question 4

How does cardiac muscle get its energy

Answer 4

It is exclusively aerobic with little or no glycogen stores

Fatty acids are the main source of energy but lactate and ketone bodies can be used

Question 5

What does cardiac muscle require

Answer 5

Requires the TCA cycle and oxidative phosphorylation

Lactate converted to pyruvate which is made into acetyl CoA

Question 6

What is adipose tissue

Answer 6

Reservoir of metabolic energy in the form of triglycerides

Question 7

How are adipose tissue filled

Answer 7

Lipids are not actually synthesised in the tissue apart from post starvation recovery
However fatty acids are made in the liver and come from our diet
Chylomicrons bring them to the tissue

Question 8

How is fat mobilisation influenced

Answer 8

Glucagon and insulin

Question 9

Kidney role

Answer 9

Main role is to produce urine

During starvation the kidney may contribute half of the blood glucose through gluconeogenesis

Question 10

What does the liver do

Answer 10

Provides fuel for the brain, muscles and other peripheral organs
Takes its energy from alpha-keto-ketoacids
Very little of the glucose is used as an energy source, most of its used for synthesis of fats or used as a temporary store in the form of glycogen

Question 11

Hexokinase vs Glucokinase

Answer 11

In non-hepatic tissue, most cells have hexokinase which phosphorylates glucose trapping it in the cell
Hexokinase is saturated at much lower levels of glucose, so its activity plateaus at much lower concentration of glucose
However glucokinase is minimally activate at low concentrations of glucose but maximally active at high concentrations of glucose

Question 12

How is glucose transported into hepatocytes =

Answer 12

GLUT-2, since its not insulin sensitive.

Its instantly phosphorylated by glucokinase

Question 13

How is glucose transported out of hepatocytes

Answer 13

Glucose-6-phosphate is converted to glucose by the action of glucose-6-phosphatase
It is then transported out of the cell and into the blood by GLUT-2 which is concentration dependant

Question 14

How is glucose taken up by muscle cells and what happens to it

Answer 14

Glucose is taken up into muscle by GLUT-4 which is insulin dependant
Its converted into G6P by hexokinase so there is a low free glucose concentration in the cell
Glycolysis of the G6P is a rapid source of ATP

Question 15

How is a sprint powered

Answer 15

ATP stores
Glycolysis
Glycogen
Creatine phosphate

Question 16

What reaction does creatine kinase facilitate

Answer 16

Creatine phosphate + ADP = ATP + creatine kinase

Question 17

What type of respiration is most effective for sprinting but what are the downfalls

Answer 17

Anaerobic respiration but produces of lactate and a fall in pH

Question 18

What is the liver Cori cycle

Answer 18

Lactate from pyruvate and amino acids from muscle protein breakdown will be converted into alanine
Alanine and lactate will be transported to the liver where it combines to form pyruvate
This pyruvate is converted into glucose through gluconeogenesis and is then transported back to the muscle

Question 19

What is the flow of molecules during the fed state

Answer 19

Initially the flow of molecules is to the liver

Then the excess glucose and fatty acids are stored

Question 20

Where is glucose stored and what is it used for

Answer 20

Stored as glycogen in the liver and used as a glucose source for the brain. It can store roughly 100g of glucose

Question 21

Where is excess glucose stored and how

Answer 21

Initially excess glucose is stored in muscle as glycogen. The muscle can store around 500g of glucose
Any extra glucose is converted to fatty acids and stored in adipocytes

Question 22

What is glucose in the liver used for and why

Answer 22

Some of it is used to make NADPH in the pentose phosphate pathway
NADPH is a substrate in fatty acid synthesis
The liver will also be making acetyl CoA for triglyceride formation

Question 23

How are fats delivered to the muscle

Answer 23

Through VLDLS, resting muscle will use fatty acids as a source of energy

Question 24

What are amino acids used for

Answer 24

Used for protein synthesis and the excess is converted to keto-acids and ultimately urea

Question 25

What processes are active in the fed state

Answer 25

Glycolysis, glycogen synthase and fatty acid synthesis are active

Question 26

What processes are inactive in the fed state

Answer 26

Glycogenolysis, gluconeogenesis and fatty acid degradation are inactive

Question 27

What molecules are produced in the fed state

Answer 27

Glycogen and fatty acids

Question 28

What molecules are not produced in the fed state

Answer 28

Glucose and ketone bodies

Question 29

Where does the body gets its energy source in the famine state

Answer 29

Glycogen and fatty acid energy stores will be used first

Lastly protein will be used as an energy source

Question 30

What happen in the post absorptive stage

Answer 30

Blood glucose will drop after several hours after the last meal
The major energy source will be glycogen

Question 31

What enzymes and hormones will be active and why

Answer 31

There will be an increase in phosphorylase a activity so glycogen breakdown will increase
Glucagon will mainly be active so normal blood glucose levels can be maintained so brain function continues

Question 32

What processes are active during the post absorptive stage

Answer 32

Glycogenolysis, gluconeogenesis and fatty acid degradation are active

Question 33

What processes are inactive during the post absorptive stage

Answer 33

Glycolysis, glycogen synthesis and fatty acid synthesis are inactive

Question 34

What molecules are produced during the post absorptive stage

Answer 34

Glucose and ketone bodies

Question 35

What molecules are not produced during the post absorptive stage

Answer 35

Glycogen and fatty acids

Question 36

What happens in early starvation

Answer 36

Glucose is released from the liver due to gluconeogenesis and glycogenolysis
Fatty acids are mobilised from adipose tissue
Glucose use falls as muscle switches to fatty acid oxidation
Insulin drops causing GLUT4 expression by muscle to fall reducing glucose uptake

Question 37

What happens in intermediate starvation

Answer 37

Glycogen stores are depleted
Increased lipolysis and ketogenesis
Increased gluconeogenesis to maintain blood glucose
Increased beta hydroxybuterate production
Further starvation sees the kidney take over gluconeogenesis from the liver

Question 38

What happens in prolonged starvation

Answer 38

Beta hydroxybuterate plateaus at 20 days
Brain starts to use ketone bodies as an energy source as well so the need for glucose drops
Lactate and glycerol are required are used as gluconeogenic precursors
Lactate is recycled back by the Cori cycle to produce pyruvate
Glycerol and amino acids are oxidised
Proteins are broken down forming amino acid precursors

Question 39

What happens to molecules produced by the skeletal muscle

Answer 39

Alanine formed from the transamination of pyruvate is released into the blood, taken up by the liver and converted into glucose
The muscle cannot form urea so the liver removes nitrogen and releases pyruvate