CBF, CSF, BBB Flashcards
what is the average cerebral blood flow?
50-100ml/100 gm of tissue/min
what is the minimum rate of cerebral blood flow
15 ml/100 gm of tissue/ min
which has higher rates, grey or white matter?
grey x2
what are the 4 regulators of CBF?
autoregulation
chemical mechanisms
neuronal control
blood viscosity
describe the innervation of cerebral arterioles
sympathetic, parasympathetic, and sensory nerves.
sensory nerves release vasoactive substances when activated that are important for headaches
describe the innervation of cerebral capillaries
innervation from raphe nuclei (serotonin), locus ceruleus (norepeinephrine), and nucleus basilis (AcH)
describe cerebral autoregulation
occurs between 70 and 160 mmHg, the muscles contract when they are stretched
results in constriction at high pressures and dilation at low pressures
how does hypertension affect autoregulation
the curve shifts to the
“right” to accomodate higher pressures
means you cannot rapidly lower blood pressure in chronic hypertension
describe the effect of pCO2 on the brain
increased CO2 causes vasodilation, decreased CO2 causes constriction
mediated by change in pH
1 mmHg change in CO2 = 2 mL/100gm/min change in flow
monro-kellie doctrine
intracranial volume is fixed and equal to brain volume + CSF + blood volume
increases in any of these will result in increased intracranial pressure
perfusion pressure =
mean arterial pressure - ICP
cushing response
elevation of blood pressure d/t increased intracranial pressure
how are changes in CBF related to changes in metabolism
metabolically active areas release vasoactive metabolites that cause an increase in CBF relative to areas that are inactive
this blood flow actually exceeds demand, meaning they have higher O2 sat (this property allows us to use magnetic imaging to look at brain)
BOLD
blood oxygen level detection functional MRI
PET scans
not as high resolution,but can be used to examine glucose metabolism
BBB purposes
- selective regulation of entry of substances
- maintains homeostatic environment
3, maintains volume
what is the BBB made of?
endothelium w/ many tight junctions and lots of mitochondria (metabolic supply for all facilitated transport)
in contact w/ astrocyte foot processes- not part of the wall itself but induce specialization
how do these substances cross the BBB?
- lipids
- small molecules
- water
- charged molecules
- nutrients
6 ions
1-3 passive
4. charge makes it more difficult to pass
5-6. need specific transporters
does K affect the brain?
not directly, but it interferes w/ normal muscle function and thus is disruptive
where in the brain isn’t there a BBB?
subfornical organ- detects and regulates osmolarity
median eminence- site of hormone release
area postrema- detects elements in blood to induce vomiting
tanicyte
cells that prevent perfusion of substances out of the hypothalamus
where is CSF formed
choroid plexus
choroid plexus capillaries are like normal capillaries
they are surrounded by epithelial cells that form the CSF/blood barrier
found in the ventricles, primarily the lateral ones
list the key differences in CSF and blood for the following:
protein, glucose, K, Ca, Mg
protein 35 v 7000 glucose 60 v 90 K 2.8 v 4.5 Ca 2.1 v 4.8 Mg .3 v 1.7
how does the CSF get into the subarachnoid space?
via the foramina of luschka and magendie at the caudal cerebellum
they exit via arachnoid granulations (mushrooms into the venous sinuses where the CSF can escape)
