Karius CSF flow Flashcards
CSF ml at any given moment around brain/SC
150 ml; not recirculated so make ~550 ml/day
The median aperture of 4th ventricle allows flow into what?
2 lateral to what?
4th ventricle to cisterna magna
4th ventricle to arachnoid space
50-70& of CSF is made by what?
Choroid plexus, the remaining is made by tissue that line the ventricles and BVs
Formation of CSF a 2-step process:
- Passive filtration of serum
2. Modification of serum
Passive filtration of serum depends on 2 pressures:
Hydrostatic pressure and oncotic pressure
hydrostatic pressure
- The pressure inside the capillary and 2.around the surrounding tissues. Inside capillary is basically blood pressure. Tissue pressure usually ‘small’ so 1 wins
Oncotic pressure
The pressure that objects pulls towards themselves. Inside capillary, proteins etc pulls pressure into capillary, same with tissues. In choroid plexus this is equal and opposite so cancels out
The modification of serum (step 2) is controlled by
channels on the epithelial cells for bicarb, Cl and K. Aquaporin 1 allows H2O to cross
Relationship between CSF production and pressure?
Production of CSF is constant over a wide range of pressures. Even if ICP is high CSF production will continue
CSF = plasma
Sodium, Na and bicarb HCO3
CSF > Plasma
Mg, Cl, CO2
CSF < Plasma
K, Ca, Protein, Glucose
Absorption of CSF is proportional to what?
ICP; below 68 mmCSF no absorb.
normal pressure = 112 mmCSF
inc. pressure will damage neurons
The main role of CSf is to what?
protect the brain. brain weight in air is 1400g in CSF is 50g
Capillaries in brain have what 2 components that limit exchange?
- Tight junctions between endothelial cells
- Glial endfeet in close contact with BVs. aka extra lipid bilayers
* this results in us needing transporters for things we want exchanged
What substances can cross BBB via passive diffusion?
H2O (via AQP4)
CO2
O2
free steroid hormones (note that most steroid hormones are protein bound)
BBB allows glucose entry via what?
glut1 transporter: not insulin dependent. 55k on caps and 45k on astroglia
glut3: allows glucose into neurons
Na/K/2Cl transporter
moves all those ions from CSF to blood. Seems to be related to [K] in CSF -if K is high starts shoving others out
Expression of the Na/K/Cl transporter controlled by what?
release of endothelin 1 & 3 from endothelial cells of the BVs
Many drugs able to cross the BBB are moved back to blood via what?
P-glycoprotein; binds to a wide variety of substances (this isnt typical of most transporters)
BBB functions mainly in
protecting chemical comp. of CSF, esp K, maintenance of Vm, protection from toxins
There are 4 areas (circumventricular organs) where we want open exchange and to handicap the BBB, we do this by what?
the capillaries do not have tight junctions between endothelial cells
the 4 circumventricular organs are:
- POST. PITUITARY -releases hormone into blood
- Area Postrema- vomiting
3,4. Organum vasculosum of the lamina terminalis (OCLT), and subfornical organ- both are involved in control of body water/thirst/blood volume
Brain blood requirements per minute are:
750 ml/min, 14% of blood pumped
The circle of willis has little blood mixing despite appearance, what is impact of this?
disruption of one of the inputs produces localized, discrete areas of ischemia
Sympathetic innervation of cerebral blood flow:
leads to constriction when systemic CO/BP increases
Sympathetic innervation of cerebral blood flow NTs and receptors?
NTs: Norepi & Neuropeptide Y(NPY)
Rec: alpha-adrenergics
Parasympathetic innervation of cerebral blood flow:
cause vasodilation, physiologic relevance uncertain
Parasympathetic innervation of cerebral blood flow NTs and Rec
NTs: Ach, VIP, PHM27 (derived from pre-pro VIP
Sensory innervation of distal brain BVs release:
Substance P, Neurokinin A, CGRP-all dilators, sense brain moving more bc weighs more
lead to pain
Local Control of cerebral blood flow by:
oxygen, consumption of oxygen will dictate where blood goes in brain
Cerebral Blood flow and MAP
Cerebral blood flow is held constant over a wide range of Mean arterial pressure. It is ‘autoregulated’ 60-140mmhg constant
In the face of high blood pressure sympathetics in the bran will do what?
vasoconstrict, although this inc. systemic vascular resistance it protects capillaries in the brain and therefore the BBB
