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BBB
Neuro Balin BBB CSF Meninges M2T2
27
Medical
Graduate
01/02/2011

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Term
Brain Barriers (4)
Definition
  • blood brain: barrier btwn blood & extracell fluid
    • endothelium
  • blood csf: barrier btwn blood & csf
    • Epithelium (tight ependyma)
  • csf brain: btwn csf & xc fluid
    • epithelium (leaky ependyma)
  • neuronal: btwn xc fluid & intracell fluid
    • not diff from most other membranes
Term
BBB capillaries
Definition
  • leaky fenestrated, selectively permeable endoth
  • Specialized endoth cells
    • NO pinocytotic vesicles, NO fenestration, NO tight jxns
  • specialized transport molec,
  • subarachnoid space
Term
Meningeal endothelia
Definition
  • Dura mater - bv = fenestrated endoth
  • Arachnoid & Pia mater: BV = NO festestrations, No tight jxn
    • component of bbb
Term
Periendothelial structures of BBB
Definition
  • Basil Lamina
    • thin bm supports abluminal surface. surrounds endoth cells & pericytes. astrocytes adjacent ot endoth cells share the basil lamina
    • components: laminin, fibronectin, tenascin, collagen, proteoglycans
    • fxn: cell attachment, migration, barirer to macromolec
  • Pericytes
    • regulate endoth cell prolif, survival, migration, differentitation, branching
    • NO alpha actin so NO contraction. gap jxns conncet w/ endoth. PHAGOCYTIC
  • Astrocytes
    • envelop 99% of bbb endothelia. intercell adhesion to endoth by both gap jxns & adherens jxn.
    • det bbb fxn, morph, prot expression. guide vessel growth by interacting cap & neurons
Term
bbb restricts
Definition
  • large molecules
  • low lipid soluble molec
  • high electrically charged molec
  • toxins/drugs
Term
Capillary Endoth
Definition
  • multi component barrier
  • physical: tight jxn (nonfenestrated) seal cell to cell contacts btwn adjacent cells
    • high electrical resistance barrier --> low paracellular perm
    • clefts btwn endoth cells so jxnal complex must constrict btwn cap endoth cells
    • diff to get thru elec barrier
Term
Jxnal Complexes
Definition
  • occludin
    • 65kD. brings opposing cell membranes into contact
    • reg prot: alter paracellular perm
  • claudins
    • form dimers that bind homtypically to claudins on adjacent endoth cell
    • 22kD
    • 4 transmembrane domains, localized TJ strand
    • from primary seal for tight jxn
  • zonula occludens
    • cytoplasmic proteins interact w/ occludin to act as recog prot for tight jxnal placement
    • number of sights for binding to cytoskel kinases & signal transduction prot
  • juctional adhesion molcules (jam)
    • localized tight jxns- members
    • members of large Ig superfamily
Term
BBB fxnal significance
Definition
  • protection/reg cns
  • Reg NT, ions, GF transfer from plasma to brain
  • Reg dietary salt water movement
  • barrier to passage of harmful substances
  • Specialized features imp for fxn
    • Inc # & vol of mito: req for active transport thru BBB
    • enzymatic barrier: metab drugs & nutrients
    • dec in cap wall thickness: allow dec transport time
    • polarity btwn luminal & abluminal surfaces
      • luminal: Gamma-GT, alk phos, P-glycoprot efflux transporter
      • abluminal: Na-KAtpase, neutral aa transporter, Glut-1-R (3:1 ablum: lum)

 

Term
BBB transport ( 3 types)
Definition
  • lipid mediation: passive
    • restricted to small lipid soluble products (drugs)
  • catalyzed transport:
    • carrier mediated: facilitated & active trasport (FAST)
    • receptor mediated transporters: slow, mostly prots
  • Transport Mechanisms
    • passive diffusion: most drugs - must be lipid soluble & unionized
    • facilitated: for CHO/AA metab subratres, carrier no ATP
    • active transport: ATP dep, vits ions
    • pinocytosis: brain cap lack sig pinocytotic vesicles, imperm to most macro molec
Term

Blood-csf Barrier

-Choroid plexus

Definition
  • fenestrated choroidal capillaries & tight jxns btwn choroidal epith
    • form & maintain CSF
    • potential leaky at base
    • small surface area
    • secretory & reabsorption fxn
      • organic acid/base pumps remove metab from csf back to c. plexus for venous drainage
  • choroid plexus cells modified ependyma cells
    • line ventricular: keep csf from going back to the brain
  • tufts of cap covered by cub epith cells
    • protrude into lumen of ventricles, secrete CSF
  • location: lat, third & 4th ventricles
Term
csf
Definition
most made in lateral ventricle then goes through ventricular system
Term
CSF brain barrier
Definition
  • leaky ependymal wall of ventricles
  • allows free exchange btwn csf & brain interstitial fluid down conc graidents
    • interstitial fluid bathes brain proper
    • dense arrangement of neurons in brain limits free diffusion of most drugs from csf to brain approx 1-1.5cm
  • circumventricular organs
Term
csf brain barrier: circumvential organs (CVO
Definition
  • brain structures that req contact w/ peripheral blood for monitoring & normal fxn
  • surface exposed to blood = fenestrated, surface exposed to brain around the ventricles = tight jxns
  • area postrema/chemoreceptor triggor zone, pit gland, pineal gland, parts of hypothalamus
  • SIGHTS WHERE BBB IS LACKIN
    • in contact w/ walls of ventricular system & lined w/ choroid plexus
    • fxnal interface btwn nervous & endocrine system
  • subfornical organ, lamina terminalis, median eminence,pineal gland, area postrmea (in 4th ventricle)
    • modified cap: fenestrated endoth, free exchange btwn blood & ecf of brain - imp in distribution of hormones in blood
Term
Meninges
Definition
  • from eyeballs to tip of spinal cord
  • foramen magnum: end cranial dura, begin spinal dura
  • Spaces
    • epidural
      • potential space btwn skull & dura
      • real space in spinal cord btwn dura & vertebral periosteum
    • subdural
      • potential space btwn dura & arachnoid
    • subarachnoid
      • csf filled space btwn arachnoid & pia
      • structural spearation by arachnoid trabeculae
  • arachnoid = translucent Dura = bery thick, pia mater
    • from skull to brain: dura, arachnoid, pia
Term
Epidural vs Subdural Hematomas
Definition
  • epidural
    • tearing of meningeal artery or venous structure
    • BIG
  • subdural
    • tearing of cerebral vein as it penetrates arachnoid & enters sinus
Term
CSF
Definition
  • NO cells
  • clear & colorless
  • lots of chloride, glc, some protein
  • fxn
    • protects the cns from trauma
    • provide mechanical buoyancy & support for the brain
    • serves as a reservoir & assists in reg of contents of skull
    • nourish cns
    • removes metab from the cns
    • serves as path for pineal secreatons to reach pit gland
Term
Ventricular system
Definition
  • filled w/ CSF
  • Lateral Vent
    • one in each cerebral hemisphere
  • third vent
    • midline cavity in diencephalon
    • communicates w/ the lat vent thru interventricular foramina
    • communicates w/ 4th vent thru cerebral aqueduct
  • fourth vent
    • btwn cerebellum, pons, medulla
Term
csf flow
Definition
  • lat vent --> interventricular foramen--> 3rd--> cerebral aqueduct --> 4th (median aperture) --> lat aperture --> ciserns (pontine & magna)
  • cerebellum sits on top of 4th vent
  • median aperture open from 4th vent straight to spinal cord so now get flow
  • cisterns accum of csf
Term
arachnoid
Definition
  • villi
    • protrude into sinuses
    • layer of endoth & arachnoid only btwn venous blood
    • major sites of csf reabsorp into venous syst
    • one way flow from subarachnoid space to venous blood
      • csf thru large vacuoles in endoth cells
      • csf movement thru channels btwn cells
  • granulations
    • groups of arachnoid villi
    • like grains of sand, csf from subarachnoid space to venous drainage
  • one way valve
Term
regulation of cerebral flow: Autoregulation
Definition
  • constant flow btwn MABP of 60-150 mmHg, rang shifts up in HTN
  • Inc Pco2- vasodialtion & inc flow
  • Dec Pco2 - vasoconstrict & dec flow
  • inc H+ (acidosis, dec neuronal active) vasodilate, inc flow
  • Dec PO2 (ischemia): vasodil & inc flow
  • INc PO2: vasoconstrict, dec flow
  • as artierial PCo2 inc, cerebral blood flow inc
Term
ICP
Definition
  • Normal ICP = 65-150 mm H20 (5-15 mmhg)
  • >20 mmHg = inc
  • only 37% of pts w/ >40mmGh for 15 min have favorable outcomes
    • when ICP >90 = cerebral circ collapes
Term
hydrocephalus
Definition
csf pressure rises & vent expand due to: excess prod csf, pappillomas, blockage of csf circ, dec csf reabsorp
Term
brain herniations
Definition
  • uncus herniation
    • through tentorial notch & pressing on midbrain
    • sever effects = pappilledema
  • tonsil herniation
    • through tonsil of cerebellum herniates thru foramen magna
    • compress medulla
  • cingulate gyrus herniation
    • subdural hematoma
Term
Cerebral perfusion pressure
Definition
  • CPP = MABP - ICP
    • as icp inc the cpp dec & correspondingly cerebral blood flow
    • vessels collapse when icp >MaBP
  • sx inc icp: headache, papilledema, altered mental status, inc bp, dec HR
  • cushing reflex
    • sign of inc icp
    • inc systolic bp, inc pulse pressure, & dec HR as ICP inc to fatal levesl
Term
3 types of cerebral edema
Definition
  • vasogenic
    • inc perm BB, inc ECF
    • usu responsive to steroids & diuretics
  • cytotoxic edema
    • hypoxia, failure of Na/K pump
    • inc intracell fluid/cell swell
    • cell filiure
  • interstitial edema
    • inc edema/fluid in white matter around vent
    • usu assoc w/ hyroccephalus
Term
empiric maneuvers to dec ICP
Definition
  • in head injury
    • hyperventilate via respirator for first 24hrs
  • elevate head of bead to 30 degrees w/ pt in midline position
  • maintain bp in normotensive range
    • high bp inc icp while low bp compromises cerebral blood flow
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