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Cerebral Blood Flow and Energy Metabolism
Dr. Salvatore
18
Anatomy
Professional
03/15/2011

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Term




*Cerebrospinal Fluid (CSF)*

Definition

Produced by choroid plexus— in lateral, 3rd, & 4th ventricles

Choroid plexus consists of capillary tufts covered by epithelium called ependyma

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The Fate of CSF

Definition

CSF is produced constantly: 21mL/hr, 500 mL/day-thus renewed 3- 4 times/day

percolates through ventricles and leaves through small openings in dura mater and into the superior sagittal sinus (venous blood blow)
Compounds entering CSF favor lipophilic ones.

Blood brain barrier refers to all interfaces between blood, brain, and CSF

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CSF Flow

Definition

Lateral ventricles converge at midline, called interventricular foramen 
3rd ventricle 
cerebral aqueduct (in midbrain) 
4th ventricle (in pons and medulla) 
foramen of Magenti OR foramen of Luschka 
subarachnoid space (bathing the brain & spinal cord and maintained by arachnoid mater
superior sagittal sinus

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CSF Functions

Definition

Cushions brain and spinal cord by absorbing shocks
Clear in color-does not normally contain blood, pus, bacteria.  Neurochemical composition determined from spinal tap
150 ml volume (total intracranial volume which includes CSF, brain, and blood is 1700 ml)
Pressure maintained by arteriolar BP
A “sink” for waste products of cerebral metabolism: CO2, lactate, H+
Normal CSF pressure = 6-13 mm Hg

Term




Monro-Kellie doctrine

Definition

brain, blood, and CSF volume determine ICP.  An increase in volume of any one will be at the expense of the other two, particularly at ICP>25 mm Hg.

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Causes of Raised ICP

Definition

Cerebral or extracerebral mass—tumor, infarction, traumatic contusion, parenchymal, subdural, or extradural hematoma

Generalized brain swelling-ichemic-anoxic states, acute hepatic failure, encephalopathy

Increase in venous pressure-thrombosis of cerebral sinuses, heart failure

Obstruction to CSF flow or absorption

Processes that increase CSF volume-meningitis, choroid plexus tumor.

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Meningeal And Opthalmic

Definition

Meningeal-ant. & post. branches of middle meningeal arteries  blood supply to dura mater, arachnoid mater, and pia materà laceration leads to epidural hematoma

Opthalmicfirst major branch of internal carotid artery.  Blood supply to the retina

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Cortical Branches

Definition

The cerebral arteries:
Anterior (1)-medial frontal & parietal lobes, motor & sensory areas for lower extremities, some basal ganglia
Middle (5)-somatic motor area (face, arm, & trunk), Broca’s area, parietal lobes, basal ganglia
Posterior (8)-occipital lobe, calcarine cortex, subthalamic nucleus, midbrain

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Cerebellar Arteries

Definition

Posterior inferior cerebellar artery—inferior surface of cerebellum, some vestibular nuclei, inf. cerebellar peduncle, spinothalamic tract, fibers of CN IX & X
Anterior inferior cerebellar artery—facial nucleus, vestibular nuclei, cochlear nuclei, inf. & middle cerebellar peduncles

Term



Central Branches
Definition


Small vessels that are branches of the larger arteries. 
Supply the basal ganglia, brain stem, cerebellum, thalamus, and hypothalamus

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Choroidal Branches

Definition

Anterior and posterior choroidal supplies the lateral ventricle

Posterior choroidal supplies the third ventricle

Branch of posterior inferior supplies fourth ventricle

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Some Major Sinuses and Veins

Definition

Great vein of Galen: receives blood from internal cerebral veins and drains into straight sinus
Straight Sinus: drains superior surface of cerbellum
Superior sagittal sinus: drains CSF from subarachnoid space & superficial cerebral veins
Inferior sagittal sinus: joins Great Cerebral vein to form straight sinus
Cavernous Sinus: receives blood from superior & inferior opthalmic veins

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Cerebral Blood Flow

Definition

Brain receives 15% of cardiac output, though comprising just 2% of body weight

Autoregulation-CBF is maintained over a BP range of 50-150 mm Hg by dilation or constriction of pial blood vessels, cerebral arteries, or arterioles. 

This feature protects the brain from changes in perfusion pressure due to increased ICP, decreased cardiac output, or even body posture changes

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Autoregulation

Definition

CBF is adjusted to metabolic need.  High plasma CO2, low tissue pH, & adenosine stimulate CBF.
Each 1 mm Hg change in arterial pCO2 produces a 2.5% change in CBF
Functional activity of brain correlates with CBF.
This activity imaged by PET scans or fMRI
Minor effect of pO2 and glucose on CBF
pCO2 very important

Term



Brain And Oxygen
Definition

Major need due to huge metabolic demand. 
ATP required for maintaining neuronal electrochemical gradient
Brain accounts for 20% of the body’s total oxygen consumption (50% or more in infants)
Brain lacks anaerobic metabolism mechanism.  

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Energy Sources

Definition

Glucose is primary source, other monocarboxylic acids (MCA) such as lactate and ketone bodies are also used

Array of transporters (glucose, MCA) exist for these compounds

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Brain And Glucose

Definition

Getting glucose in:  facilitated diffusion across the BBB via glucose transporters GLUT1, -2, -3

GLUT1 located on brain endothelial cells of the BBB and on astrocytic processes called endfeet in association with capillaries.
Delivery of glucose from blood to brain occurs 1) through these endfeet, 2) directly into neurons, and 3) into the glia.

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GABA-Glutamate-Glutamine Cycle

Definition

-Interaction between TCA cycle with neurotransmitter biosynthesis via α-ketoglutarate.  Glutamate & GABA are the major excitatory and inhibitory neurotransmitters of the CNS.  


Direct, one-step reaction of α-ketoglutarate (α-KG) in an amino-group transfer reaction or transamintation of α-oxoglutatrate
the glutamine cycle. Gln released from glia is taken up by neurons and converted into glu by glutaminase (50% of neuronal glutamate derived from this cycle).
Glutamate is in equilibrium with a-ketoglutarate.  The glutamine cycle is critical for offsetting loss of α-KG from the TCA cycle.

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