CSF & intracranial pressure Flashcards
(37 cards)
where is CSF located
between the ventricles and subarachnoid space
2 main types of meninges
- dura mater (pachymeninges)
- leptomeninges
- arachnoid
- pia
CSF production and the process involved
mostly produced by the choroid plexus
-mainly in lateral ventricles
involves 2 processes
- ultrafiltration across choroidal capillary wall
- active secretion by choroidal epithelium
choroid plexus structure
- fenestrated capillary network surrounded by a row of epithelial cells
- choroid plexus epithelial cells have tight junctions between them. They contain vesicles and lysosomes and have a microvilli brush border
CSF circulation
- CSF produced in lateral ventricles
- travels trough foramina munro
- goes into the midline of the 3rd ventricle
- passes through the sylvian aqueduct into 4th ventricle
- then leaves out through 3 foramen into subarachnoid space
CSF absorption
majority via the small arachnoid villi and larger arachnoid granulations
(herniations of arachnoid mater through dura into superior sagital sinus)
absorb CSF by unidirectional ‘bulk flow’
CSF total volume
150ml
mostly in subarachnoid space
(some in ventricles)
rate of CSF production
600ml/day
0.35ml/min
what does CSF absorption depend on
hydrostatic pressure in subarachnoid space
- not regulated by any transport process
CSF composition
clear and colourless
- WBC <5x10^6/L
- no neutrophils
- no RBC
- protein <0.45g/L
- glucose >2.5mmol/l
CSF changes in meningitis
increase WBC
increase protein
some cause low glucose (bacterial meningitis)
CSF in subarachnoid haemorrhage
increase in RBC
‘xanthochromia’ (yellow discolouration due to RBC breakdown - takes time)
CSF function
maintains environment for neurons and glia
mechanical cushion for brain
counters sudden increases in intracranial pressure
function of the BBB
- regulation of ionic balance in brain
- facilitates transport of essential substrates into brain e.g. oxygen
- barrier against the entry of potentially harmful molecules
metabolites need to be selectively transported across the endothelial cells
what does the BBB consist of?
- specialised endothelial cells
- thick basement membranes
- astrocytic processes on capillaries
describe the differences between systemic endothelial cells and brain endothelial cells
intracellular junctions
- systemic = fenestrated
- brain = tight
pinocytotic vesicles
- systemic = common - brain = uncommon
basement membrane
- systemic = thin - brain = thick
mitochondria
- systemic = + - brain = +++
transport across BBB
diffusion
-lipid soluble substances e.g.O2/CO2
active transport
- energy dependent
- glucose, some AA, vitamins
ion channels
factors affecting passage of molecule across BBB
- molecular weight (size)
- lipid solubility
- ionisation
- protein binding
- transport mechanism
disease processes involving the BBB
- disruption of tight junctions
- disruption of BM
- disruption of endothelial-astrocyte interaction
- altered function of specific transporter
- new BVs lacking features of BBB
how does meningitis affect the BBB
inflammatory response causes BBB breakdown
white cells and protein in the CSF
how do brain tumours affect the BBB
- abnormal BVs
- vessels can be ‘leaky’
- interstitial fluid accumulates (oedema)
how is intracranial pressure measured
- lumbar puncture
- intracranial pressure monitoring
normal CSF pressure
= 65-195mm of CSF (or water)
= 5-15mmHg
what are the 3 components of the intracranial contents and there values
brain 1300-1500mL
blood 75mL
CSF 75mL
intracranial volume fixed by skull
