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Adult brain blood flow
700-800ml/min = 50ml/100g/min
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Changes in blood flow
- <20 ml/100g/min: ischaemia
- <10: infarction
- >60: hyperaemia - raised pressure/indicative of tumour
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3 types of strokes
- Thrombotic (50%): plaques
- Embolic (30%): dislodged clots
- Haemorrhagic (20%): bursts
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Define transient ischaemic attack
Stroke lasting for <24 hours: can indicate risk of major stroke
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Blood supply of bits of brain
- Ant. Cerebral: medial aspects of cortical hemispheres forward of parieto-occipital border
- Mid. Cerebral: lateral aspects of cortical hemispheres, basal ganglia, internal capsule
- pos. cerebral: occipital lobe, pos-inf surface of temporal lobe, diencephalon, midbrain
- Sup. Cerebellar: and pons
- ant. Inf. Cerebellar: and pons
- pos. inf. cerebellar: and medulla
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Features of BBB
Tight junctions, astrocytic foot processes
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Function of BBB
- Prevent exogenous toxins reaching brain
- Prevent harmful endogenous substances reaching brain
- Allow essential substances to reach neurones and glia
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Things and how they are transported across BBB
- Facilitated diffusion: amino acids, glucose, L-DOPA (via a system normally used by AAs)
- Active transport: amino acids
- Diffusion: lipophilic things (eg drugs)
- Active ion exchange
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Where BBB is absent
- Circumventricular organs eg pineal gland (sensory/receptive)
- Choroid plexus
- Neurological disorders
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CSF found in
- ventricles
- central canal of spinal cord
- subarachnoid space
- cisterns (Expansions of subarachnoid space)
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Function of CSF
- cushion brain against trauma
- removes harmful metabolites from ECF
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Choroid plexus present in
lateral, 3rd, 4th ventricles
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How much CSF secreted per day
~500ml
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Choroid epithelium formed by
- pia mater (surrounding blood vessels)
- ependyma (lining ventricles)
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Transport across choroid epithelium
- similar to BBB (tight junctions)
- specialised transport mechanisms eg facilitated diffusion, ion exchange, active transport
- 'Blood-CSF barrier'
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4 differences between blood and CSF
- 1. much less protein in CSF
- 2. small numbers of lymphocytes in CSF
- 3. no RBCs in CSF
- 4. CSF has half the [glucose] found in blood
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Eg of when CSF content changes
bacterial meningitis - becomes cloudy, contains more protein and RBCs
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How much CSF is removed per day? How?
~400ml via arachnoid villi in arachnoid mater in dural sinuses
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Blood drainage in brain
- superficial cerebral veins in white matter and cortex ? sup/inf sagittal sinuses ? straight sinus
- deep veins (basal ganglia and diencephalon) ? great cerebral vein ? straight sinus
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