Integration of whole body metabolism Flashcards
How much energy does the brain use and what is it used for
- 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
How is glucose transported in the brain
GLUT3, which has a low Km therefore is saturated at low glucose concentrations
Why aren’t fatty acids used for energy
Since they are used membrane biosynthesis
How does cardiac muscle get its energy
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
What does cardiac muscle require
Requires the TCA cycle and oxidative phosphorylation
Lactate converted to pyruvate which is made into acetyl CoA
What is adipose tissue
Reservoir of metabolic energy in the form of triglycerides
How are adipose tissue filled
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
How is fat mobilisation influenced
Glucagon and insulin
Kidney role
Main role is to produce urine
During starvation the kidney may contribute half of the blood glucose through gluconeogenesis
What does the liver do
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
Hexokinase vs Glucokinase
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
How is glucose transported into hepatocytes =
GLUT-2, since its not insulin sensitive.
Its instantly phosphorylated by glucokinase
How is glucose transported out of hepatocytes
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
How is glucose taken up by muscle cells and what happens to it
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
How is a sprint powered
ATP stores
Glycolysis
Glycogen
Creatine phosphate
What reaction does creatine kinase facilitate
Creatine phosphate + ADP = ATP + creatine kinase
What type of respiration is most effective for sprinting but what are the downfalls
Anaerobic respiration but produces of lactate and a fall in pH
What is the liver Cori cycle
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
What is the flow of molecules during the fed state
Initially the flow of molecules is to the liver
Then the excess glucose and fatty acids are stored
Where is glucose stored and what is it used for
Stored as glycogen in the liver and used as a glucose source for the brain. It can store roughly 100g of glucose
Where is excess glucose stored and how
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
What is glucose in the liver used for and why
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
How are fats delivered to the muscle
Through VLDLS, resting muscle will use fatty acids as a source of energy
What are amino acids used for
Used for protein synthesis and the excess is converted to keto-acids and ultimately urea
What processes are active in the fed state
Glycolysis, glycogen synthase and fatty acid synthesis are active
What processes are inactive in the fed state
Glycogenolysis, gluconeogenesis and fatty acid degradation are inactive
What molecules are produced in the fed state
Glycogen and fatty acids
What molecules are not produced in the fed state
Glucose and ketone bodies
Where does the body gets its energy source in the famine state
Glycogen and fatty acid energy stores will be used first
Lastly protein will be used as an energy source
What happen in the post absorptive stage
Blood glucose will drop after several hours after the last meal
The major energy source will be glycogen
What enzymes and hormones will be active and why
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
What processes are active during the post absorptive stage
Glycogenolysis, gluconeogenesis and fatty acid degradation are active
What processes are inactive during the post absorptive stage
Glycolysis, glycogen synthesis and fatty acid synthesis are inactive
What molecules are produced during the post absorptive stage
Glucose and ketone bodies
What molecules are not produced during the post absorptive stage
Glycogen and fatty acids
What happens in early starvation
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
What happens in intermediate starvation
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
What happens in prolonged starvation
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
What happens to molecules produced by the skeletal muscle
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
