Cerebral Vasculature and Brain Homeostasis Flashcards
What are the 4 main fluid compartments of the brain?
- CSF = 10%
- blood = 10%
- IF = 12-20%
- Intracellularfluid = 60-80%
How much CSF is there and how often is it renewed?
~150 mL
renewed every ~ 6 hrs (550 mL/day)
What are the 3 areas CSF lives?
ventricles
cisterns
subarachnoid space
How does CSF help the brain?
creates bouyancy
How does water flow through choroid plexus epithelial cells?
from blood (basolateral side) to ventricular lumen (apical)
What transporters are on the apical membrane of choroid plexus cells?
Na/K-ATPase
aquaporin
What transporters are on the basolateral/blood side of choroid plexus cells?
NCBE
aquaporin
How do choroid plexus cells move water from the blood to ventricles?
Na/K-ATPase creates electrochemical gradient for Na –> net flux of Na, HCO3 and Cl- into ventricles
water follows via osmosis
What type of aquaporin is in choroid plexus cells?
AQP 1
What things are in the same concentration in CSF and serum?
Na
osmolarity
What things are found in greater concentration in CSF compared to Serum?
Cl-
CO2
H+ (pH is more acidic)
What things are found in greater concentration in serum than CSF?
Protein* glucose* (pH more basic) K+ Ca Mg HCO3
How are absorption of CSF and intracranial pressure related?
absorption of CSF is proportional to ICP
ICP < 68 mm Hg, no absorption occurs
normal = 112
How does blood CO2 affect cerebral blood flow?
increased CO2 in blood greatly increases cerebral blood flow
What is normal cerebral blood flow?
750-900 mL/min
How do sympathetics and parasympathetics affect cerebral circulation?
Sympathetics: vasoconstriction when CO or BP increases
Parasympathetics: vasodilation when BP decreases (get more blood to the brain)
What NTs and receptors do sympathetics use to alter cerebral circulation?
NE and NPY
alpha adrenergic
What NTs do parasympathetics use to alter cerebral circulation?
Ach
VIP
CGRP
SP
How are cerebral vessels innervated?
very sensitive to torsion/manipulation –> pain
decreased CSF vol –> brain heavier –> pain
How does ICP affect cerebral blood flow?
increased ICP –> obstruction of venous outflow –> reduced arterial flow
How are Pa O2 and cerebral blood flow related?
as O2 increases –> flow decreases steeply at first –> plateaus at 50 mL/100 g/min
How are cerebral perfusion pressure and cerebral blood flow related?
increase together steeply at first –> blood flow plateaus at about 50 mL/100 g/min
will then increase again if perfusion pressure gets above 200
What mediates autoregulation?
sympathetic stimulation
What is the purpose of vasoconstriction?
increases systemic vascular resistance
BUT
protects the BBB and capillaries
