3. • SOME FACTS………………
• Brain is one of the most metabolically active organs in the body
• At rest, it uses approximately 20% to 23% of the body’s total
energy requirements, despite accounting for only 2% of the
body’s mass
• About 750 ml of blood per min
• Neurons can survive only a few minutes without blood supply
4. • Unconsciousness : with in 10 sec after occlusions
• No stored fuel in brain
• Total consumption of glucose by brain : 120 gm/day out of
160 gm/day ( 480kcal)
• Brain cannot utilize fatty acids since it is combined with
albumin and cannot cross BBB.
5. • Glucose from blood enters the brain by a transport protein
– Glucose transport protein (GLUT-1) is highly enriched in
brain capillary endothelial cells
• Glucose is the primary energy substrate for the brain
– Glycolysis
– Pentose phosphate pathway
– Glycogenesis (only in astrocytes)
• Brain stores little energy as glycogen and relies almost
entirely on circulating glucose for fuel
– to maintain synaptic function and resting potential of
neurons
Brain relies on glucose for energy
9. • During starvation:
– Brain can use ketone bodies in place of glucose as
substrates
– Ketone bodies; acetocetate and β-hydroxybutyrate
are formed from catabolism of fatty acids by the
liver (60-70% as brain fuel)
– They are metabolized to generate acetyl-CoA which
enters the TCA cycle to meet the metabolic demand
of the brain
10. I II III IV V
0-4HRS 4-16HRS 16-32HRS 32HRS-24DAY 24DAYS AND
ON
ORIGIN OF
BLOOD
GLUCOSE
EXOGENOUS GLYCOGEN,
HEPATIC
GNG
HEPATIC
GNG,
GLYCOGEN
HEPATIC &
RENAL GNG
HEPATIC &
RENAL GNG
MAJOR FUEL
OF BRAIN
GLUCOSE GLUCOSE GLUCOSE GLUCOSE,
KETONE
BODIES
KETONE
BODIES,
GLUCOSE
11. Exam point of view
• Fuels for the brain is glucose, ketone bodies
and branched chain amino acids
• Per day , total glucose utilization = about 120
gm out of 160 gm
• For our brain , Its blood glucose
12.
13.
14. During late starvation
• Major fuel : 1) ketone bodies ( acetoacetate and beta hydroxyl
butyrate) and 2) branched chain amino acids
• Minor fuel: glucose via gluconeogenesis in liver and kidney
• Insulin: glucagon ratio decreased
• In adipose tissue, stimulate hormone sensitive lipase
• TAG is broken down to free fatty acid and glycerol
• Under goes beta oxidation
• Production of acetyl CoA which is the precursors for ketone
bodies
20. • This shuttle process is vital for proper synaptic
glutamate release because neurons do not express
enzymes for de novo synthesis of glutamate, so
neuronal glutamate is entirely derived from astrocyte
glutamine or α-ketoglutarate
• Astrocytes produce de novo glutamate or glutamine
from glucose via pyruvate conversion to oxaloacetate
by pyruvate carboxylase
