Cerebral Vasculature & Brain Homeostasis Flashcards
What connects the lateral ventricles to the 3rd ventricle?
Intraventricular foramen
What connects the 3rd ventricle to the 4th ventricle?
Cerebral aquaduct
What connects the 4th ventricle to the cisterna magna?
Median aperture
What connects the 4th ventricle to the arachnoid space?
Lateral apertures (2)
What produces CSF?
Choroid plexus (50-70%), mostly in the lateral ventricle
What are the 2 steps of CSF production?
Passive filtration of serum and modification of ion composition
The passive filtration of serum is dependent on what two pressures?
Hydrostatic pressure of the capillaries (pushes fluid out of capillaries in the brain) and oncotic pressure (dependent on solute concentration in the blood, is equal in brain)
How much CSF do we have at any given moment? How much is produced per day?
150ml at any given moment
550ml made per day
What ions are at the same concentration in CSF vs in the blood?
Na+ and HCO3
What ions have a higher concentration in CSF vs in the blood?
Mg2+, Cl-, CO2
What ions have a lower concentration in CSF vs in the blood?
K+, Ca2+, protein, glucose
What reabsorbs the CSF?
Arachnoid villi (where pia and arachnoid mater have fused). Flow of CSF from subarachnoid space into sinuses
The absorption of CSF is proportional to what?
ICP (normal pressure is 112 mm CSF). Absorption happens over 68 mm CSF
Increased CSF pressure does what?
Damages neurons
What are the two components of the BBB?
Tight junctions between endothelial cells and glial endfeet that come in contact with the blood vessel (cover capillary w/ lipid bilayers)
What can cross the BBB via passive diffusion?
H20 (aquaporin 4), CO2, O2, and free steroid hormones
How does glucose cross the BBB?
Glut1 transporter, is not insulin dependent
55K on capillaries
45K on astroglia
How does glucose get into neurons?
Glut3 transporter (is also insulin independent)
What is the Na/K/2Cl transporter?
Moves all those ions from CSF to blood when [K+] of CSF is too high
What is P-glycoprotein?
Pump that binds to a wide variety of chemicals and moves them out of the CSF back into the blood
Where are the circumventricular organs?
Posterior pituitary (releases hormones into the blood) Area postrema (chemotactic trigger zone for toxins in blood) Organum vasculosum of lamina terminalis (OVLT) and Subfornical organ (control of body osmolarity)
What is the significance of the circumventricular organs?
Not as well protected by BBB as other neural tissue so they can be exposed to the blood.
What NTs are involved in sympathetic innervation of cerebral circulation?
Norepinephrine and neuropeptide Y
Go to alpha-adrenergics (vasoconstriction)
What NTs are involved in parasympathetic innervation of cerebral circulation?
Ach, VIP, and PHM-27 cause vasodilation
What NTs are involved in sensory innervation of cerebral circulation?
Substance P, neurokinin A, and CGRP (all dilation)
What is the clinical relevance of sensory fibers in the brain blood vessels?
Extremely sensitive to torsion/manipulation. Brain heavier in presence of reduced CSF volume and causes torsion of blood vessels. Induces vasodilation to increase blood flow and return intracranial volume closer to normal
In response to high systemic BP, what do sympathetics in the brain do?
Vasoconstrict to protect capillaries in the brain and BBB from damage
What does high ICP mean in terms of blood flow? What does the brain do to counteract this?
Means venous outflow from brain is obstructed so there is reduced arterial flow into the brain. Brain drives up systemic BP to force blood into the brain
