Brain Metabolism - Tucker Flashcards
What are three causes of increased intracranial pressure?
- Anoxia
- Ischemic stroke
- Hemmorrhage
What are 5 ways the brain gets energy?
- Glucose
- Ketone Bodies
- Lactate
- Amino Acids
- Fatty Acids
Where is glycogen in the brain stored?
In astrocytes
Synthesis and storage of glycogen occurs primarily in astrocytes - Much smaller amount of glycogen in brain compared to liver and muscle - Acts as an energy buffer - Would last only a few minutes if used exclusively
What glucose transporters (and for which cells) are used in the brain?
Transporters
GLUT 1 - Astrocytes & Endothelial Cells
GLUT 3 - Neurons
For an adult at rest, > ___% of glucose is metabolized ____ (by neurons).
Evidence exists for preferred metabolic pathways in ___ vs ____
For an adult at rest, > 90% of glucose is metabolized aerobically (by neurons)
Evidence exists for preferred metabolic pathways in astrocytes vs neurons
Astrocyte-Neuron Lactate Shuttle
Even when O2 is readily available, studies have shown that _____ glycolysis occurs in ___ during activation.
The ____ can then be used by ___ after conversion back to ___.
____ –> use more glycolysis
____ (which require more energy) –> use more oxidative phosphorylation, which generates more ___
Astrocyte-Neuron Lactate Shuttle
Even when O2 is readily available, studies have shown that anaerobic glycolysis occurs in astrocytes (a for a) during activation.
The lactate can then be used by neurons after conversion back to pyruvate.
Astrocytes –> more glycolysis
Neurons (which require more energy) –> more oxidative phosphorylation, which generates more ATP.
Flow-Metabolic Coupling
What is it?
Flow-Metabolic Coupling
When the cortex is activated, oxygen and glucose consumption is matched with cerebral blood flow
How much O2 and Glucose Does the Brain Use?
How much O2 and Glucose Does the Brain Use?
Brain normally extracts 50% of available oxygen and 10% of available glucose from the blood
What happens if you have decreased blood flow to the brain?
Oxygen and glucose extraction increases to maintain necessary metabolic processes
Other Ways to Mediate BF Changes
___, ____, _____, ___, ____ acid metabolites, and ___ oxide mediate blood flow changes (CBF is tightly coupled to local cerebral metabolic needs).
Other Ways to Mediate BF Changes
Hydrogen, potassium, neurotransmitters, adenosine, arachidonic acid metabolites, and nitric oxide mediate blood flow changes (CBF is tightly coupled to local cerebral metabolic needs).
Branches of cerebral arteries run along surface of brain.
SMC’s lining the arteries respond to ___ __ and ____ mediators to cause changes in blood vessel ___
Branches of cerebral arteries run along surface of brain
SMC’s lining the arteries respond to intravascular pressures and vasoactive mediators to cause changes in blood vessel diameter
Brain maintains constant ____ despite CPP / MAP fluctuations by changing caliber of __ __
Brain maintains constant CBF despite CPP / MAP fluctuations by changing caliber of pial arterioles
Autoregulation works well if:
MAP/CPP __ to ___ mmHg.
Outside this range, the CBF varies directly with __ __.
Loss of ___ can be focal or global in brain injury (stroke, TBI, SAH, anoxic brain injury)
MAP / CPP too low –> vessels cannot ___ any further to compensate, so you get __ injury.
MAP/CPP too high –> causes ___ pressure inside vessels, overcomes maximal ____. ____ is disrupted, causing _____ –> leading to __ ___+/- hemorrhage
Autoregulation works well if:
MAP/CPP 60 to 150 mmHg.
Outside this range, the CBF varies directly with perfusion pressure.
Loss of autoregulation can be focal or global in brain injury (stroke, TBI, SAH, anoxic brain injury)
MAP / CPP too low –> vessels cannot dilate any further to compensate, so you get ischemic injury.
MAP/CPP too high –> causes increased pressure inside vessels, overcomes maximal constriction. BBB is disrupted, causing HYPER-PERFUSION –> leading to CEREBRAL EDEMA +/- hemorrhage
Decrease in ___ - VASOCONSTRICTION
Increase in ___ - VASODILATION
Decrease in ___ - VASODILATION
Decrease is PCo2 - VASOCONSTRICTION
Increase in PCo2 - VASODILATION
Decrease in PO2 - VASODILATION
What are 5 diagnostic tools you can use for increased intracranial pressure?
TP CMC
- Transcranial Doppler Ultrasound measurement of blood flow velocities in major vessels – can evaluate for autoregulation by manipulating PaCO2.
- PET Evaluates cerebral metabolism – usually glucose uptake
- CT Perfusion Evaluates blood flow, volume, mean transit time to look for penumbra
- MR Perfusion - Pulsed arterial spin labeling (shows cerebral perfusion)
- Cerebral Microdialysis Evaluates cerebral metabolism by measuring local metabolites)
