CBF, CSF, BBB

Question 1

what is the average cerebral blood flow?

Answer 1

50-100ml/100 gm of tissue/min

Question 2

what is the minimum rate of cerebral blood flow

Answer 2

15 ml/100 gm of tissue/ min

Question 3

which has higher rates, grey or white matter?

Answer 3

grey x2

Question 4

what are the 4 regulators of CBF?

Answer 4

autoregulation
chemical mechanisms
neuronal control
blood viscosity

Question 5

describe the innervation of cerebral arterioles

Answer 5

sympathetic, parasympathetic, and sensory nerves.

sensory nerves release vasoactive substances when activated that are important for headaches

Question 6

describe the innervation of cerebral capillaries

Answer 6

innervation from raphe nuclei (serotonin), locus ceruleus (norepeinephrine), and nucleus basilis (AcH)

Question 7

describe cerebral autoregulation

Answer 7

occurs between 70 and 160 mmHg, the muscles contract when they are stretched

results in constriction at high pressures and dilation at low pressures

Question 8

how does hypertension affect autoregulation

Answer 8

the curve shifts to the
“right” to accomodate higher pressures

means you cannot rapidly lower blood pressure in chronic hypertension

Question 9

describe the effect of pCO2 on the brain

Answer 9

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

Question 10

monro-kellie doctrine

Answer 10

intracranial volume is fixed and equal to brain volume + CSF + blood volume

increases in any of these will result in increased intracranial pressure

Question 11

perfusion pressure =

Answer 11

mean arterial pressure - ICP

Question 12

cushing response

Answer 12

elevation of blood pressure d/t increased intracranial pressure

Question 13

how are changes in CBF related to changes in metabolism

Answer 13

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)

Question 14

BOLD

Answer 14

blood oxygen level detection functional MRI

Question 15

PET scans

Answer 15

not as high resolution,but can be used to examine glucose metabolism

Question 16

BBB purposes

Answer 16

1. selective regulation of entry of substances
2. maintains homeostatic environment
   3, maintains volume

Question 17

what is the BBB made of?

Answer 17

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

Question 18

how do these substances cross the BBB?

1. lipids
2. small molecules
3. water
4. charged molecules
5. nutrients
   6 ions

Answer 18

1-3 passive
4. charge makes it more difficult to pass
5-6. need specific transporters

Question 19

does K affect the brain?

Answer 19

not directly, but it interferes w/ normal muscle function and thus is disruptive

Question 20

where in the brain isn’t there a BBB?

Answer 20

subfornical organ- detects and regulates osmolarity

median eminence- site of hormone release

area postrema- detects elements in blood to induce vomiting

Question 21

tanicyte

Answer 21

cells that prevent perfusion of substances out of the hypothalamus

Question 22

where is CSF formed

Answer 22

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

Question 23

list the key differences in CSF and blood for the following:

protein, glucose, K, Ca, Mg

Answer 23

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

Question 24

how does the CSF get into the subarachnoid space?

Answer 24

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)