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Neuroscience > L21 Transport within the CNS > Flashcards

L21 Transport within the CNS Flashcards

1
Q

list the fluid compartments in the CNS

A 
Brain volume total = 1200 mL
ICF = 720 mL
ECF = 480 mL
    - Blood plasma = 70mL
    - Interstitial fluid = 260 mL
    - CSF = 90-140 mL
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2
Q

list the main constituents of the CSF compared to plasma

A 
low in (compared to plasma)
-pH, protein, glucose, K+ Ca+
high in (compared to plasma)
-Na, Cl, Mg2+
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3
Q

what are the functions of CSF?

A
  • maintaining constant extracellular environment
  • removal of metabolites from brain
  • changes in CSF pH = influences pulmonary ventilation rate and cerebral blood flow
  • cushion between brain and skill (shock absorption + buoyancy)
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4
Q

where does CSF circulate?

A
  • Ventricles
    lateral ventricles – foramen of Monroe – 3rd ventricle – cerebral aqueduct — 4th ventricle — lushka and magendie
  • spinal canal
  • subarachnoid space
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5
Q

where does CSF travel after the 4th ventricle?

A

passes into the subarachnoid space and central spinal canal

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6
Q

at what level is a lumbar puncture/spinal tap performed?

A

L3/L4 levels in adult

L4/L5 level in children

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7
Q

what can spinal tap/lumbar puncture diagnose? what is the normal value?

A

infections - meningitis
stroke
spinal cord tumor
cancer in CNS

65-200 mm water/ 5-15 mmHg

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8
Q

describe the site of the BBB

A

endothelial cells - with tight junctions in between
astrocyte endfeet
capillary basement membrane

transcellular routes through endothelial cells

allows gases and glucose uptake

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9
Q

what are the mechanisms of solute transport across the BBB

A

transcellular only!

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10
Q

what does the rate of transcellular transport depend on?

A

lipid solubility - the higher the oil/water partition coefficient is, the better transfer through phospholipid membranes

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11
Q

what things can diffuse through BBB?

A 
blood gases
small hydrophobic molecules
small uncharged bipolar molecules
water
glycerol
urea
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12
Q

how does glucose and L-DOPA get into brain?

A

facilitated diffusion
Glucose – GLUT 1 transporter (faster)
L-DOPA transporter - carrier for neutral aa

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13
Q

how does glycine get into the BBB from the brain into the blood?

A

secondary active transport – co transport with Na+

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14
Q

what things can cause the BBB to become permeable (endothelial cell shrink - tight junctions open)?

A
  • htn
  • hyperosmolality
  • inection - HIV
  • trauma, ischemia, inflammation, pressure
  • toxic compounds, metals (Pb2+)
  • lymphocytes can cross over from blood to brain - chemokine receptors involved CCR5
  • they open BBB if they want to intro lipid insoluble drugs to CNS
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15
Q

what organs are affected with a permeable BBB?

A

circumventricular organs

  • area posterma
  • pineal body
  • subcommissural organ
  • subfornical organ
  • organum vasculosum of lamina terminals (OVLT)
  • neurohypophysis
  • median eminence
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16
Q

describe the site of the blood-CSF barrier

A

ventricular lining
-ependymal cells (group 2) + gap junctions

choroid plexus
-secretory ependymal cells (group 1) - produce CSF ++ tight junctions

17
Q

distinguish between mech. of solute (and water) transfer across BBB and blood-CSF barrier and those operating across the ependymal cells lining the ventricles

A

basolateral membrane - co transporters for Na+, K+, Cl-

Apical membrane microvilli - co transporters for K+ and Cl-…. Na+, K+ and Cl- ion channels…. Na/K pump

ions are accompanies by transport of water by local osmosis

18
Q

where is CSF absorbed and returned to venous circulation?

A

by arachnoid granules in lumen of superior sagittal sinus

19
Q

list the main disturbances in the composition of the CSF (cells in CSF, protein, glucose) obtained from pt suffering from bacterial meningitis?

A
  • cells in CSF = high polymorphonuclear neutrophils/leukocytes 1000/<5
  • protein = high 500/35
  • glucose = low 20/60
20
Q

list the main disturbances in the composition of the CSF (cells in CSF, protein, glucose) obtained from pt suffering from viral meningitis

A
  • cells in CSF = high lymphocytes 500/<5
  • protein = high 500/35
  • glucose = normal
21
Q

list the main disturbances in the composition of the CSF (cells in CSF, protein, glucose) obtained from pt suffering from brain tumor or abscess

A
  • cells in CSF = high lymphocytes 500/<5
  • protein = high 500/35
  • glucose = normal (sometimes can be lower)
22
Q

list the main disturbances in the composition of the CSF (cells in CSF, protein, glucose) obtained from pt suffering from multiple sclerosis

A
  • cells in CSF =normal, but IgG increased + changes in T lymphocytes!
  • protein = normal
  • glucose = normal
23
Q

list the main disturbances in the composition of the CSF (cells in CSF, protein, glucose) obtained from pt suffering from Guillain-Barre syndrome

A
  • cells in CSF = 50/35

- glucose = normal

24
Q

list the main disturbances in the composition of the CSF (cells in CSF, protein, glucose) obtained from pt suffering from Subarachnoid hemorrhage

A
  • cells in CSF = RBCs
  • protein = high
  • glucose = normal
25
Q

what is the cause of communicating hydrocephalus?

A
  • Due to malabsorption of CSF due to thickening of the arachnoid villi due to several pathologies
  • Enlargement of ALL ventricles will always occur in communicating
  • PAPILLOMAS: tumors of the choroid plexus can (but rarely) cause communicating by secreting CSF in great excess
  • excess CSF secretion unmatched by rate of CSF drainage - increase ICP
26
Q

what is the cause of non-communicating hydrocephalus?

A
  • Due to blockage of CSF flow thus an enlargement of the ventricles above the blockage
  • Enlargement of the Lateral Ventricles ALWAYS occurs in non-communicating/obstructive
27
Q

what is normal pressure hydrocephalus?

A
  • symptoms are aging/loss of cognitive ability, disturbances of walking and urinary incontinence
  • enlarged ventricles, sulci, fissures with a flattening of cortical gyri against skull
  • reduction in brain volume
  • decrease in cellular volume of brain
28
Q

what does the Monroe-Kellie doctrine state?

A

if there is a tendency for a fluid compartment of the brain to increase (e.g. tumor, abscess) there must be a corresponding decrease in another compartment or ICP will rise!

29
Q

what is the cause of vasogenic brain edema?

A
  • origin = increase cap. permeability
  • location = W and G matter
  • composition of edema fluid = plasma filtrate (with proteins)
  • cap permeability to large mol. = increased
  • disorders = brain tumor, abscess, trauma, hemorrhage
30
Q

what is the cause of cytotoxic brain edema?

A
  • origin = **neuronal and glial swelling - why? - blood supply, oxygen/glucose = low, ATP and Na/K pump tired, ion gradients fucked up
  • location = W and G matter
  • composition of edema fluid = increased intracel. water and Na
  • cap permeability to large mol. = normal
  • disorders = hypoxia, water intoxication, ischemia
31
Q

how do tumor get blood supply?

A

paracellular transport

32
Q

what is congenital hydrocephalus?

A
  • cerebral aqueduct blocked/not formed - dilate lateral ventricles
  • dandy-walker syndrome - foramen of lushka and magendie not developed - dilation of all ventricles
33
Q

what increases ICP

A
  • hydrocephalus
  • tumor growth
  • IC hemorrhage
34
Q

what are symptoms of ICP increases?

A
  • nausea
  • bradycardia
  • systemic htn
  • loss of consciousness
  • papilledema (optic disc swelling )
35
Q

what decreases ICP

A

head injury
dehydration
spinal tumor

Neuroscience (54 decks)

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