cerebral blood flow and CNS homeostasis Flashcards
What is the impact of the little mixing of the blood from the different sources in the brain?
disruption of one of the inputs produces localized (discrete) areas of ischemia–> there will not be a global ischemic event–> protective mechanism
What are the neurotransmitters involved in the sympathetic innervation of the cerebral circulation?
norepinephrine and neuropeptide Y (NPY)
What are the receptors for the neurotransmitters involved in the sympathetic innervation of the cerebral circulation?
alpha-adrenergic receptors
What happens when norepinephrine or NPY bind to an alpha adrenergic receptor?
it causes vasoconstriction
What type of blood vessels are involved in the parasympathetic innervation of the cerebral circulation?
larger blood vessels
what is the major neurotransmitters of the parasympathetic innervation of the cerebral circulation?
ACh, Vasoactive intestinal polypeptide (VIP) and PHM-27
what do the neurotransmitters involved in the parasympathetic innervation of the cerebral circulation cause?
vasodilation
Besides the sympathetic and parasympathetic innervation of the cerebral circulation, there is an additional source of innervation. What is it?
sensory innervation of the distal blood vessels
distal blood vessels will contain nociceptors. These nociceptors will release neuropeptides when the blood vessels of the brain experience torsion/manipulation. What are these neuropeptides?
substance P, neurokinin A, and CGRP
When does torsion/manipulation of the brain’s blood vessels occur?
in the presence of reduced CSF
The activation of those afferent C fibers will also cause what in addition to causing pain?
vasodilation and increase the blood flow
What kind of control is cerebral blood flow under?
local control
what does it mean when it is said that cerebral blood flow is under local control?
oxygen consumption dictates where in the brain the blood will go
What does it mean when it is said that cerebral blood flow is strongly autoregulated?
it is held constant over a wide range of systemic (mean arterial) blood pressures
At about what pressure does the brain begin to autoregulate the cerebral blood flow?
~60 mmHg
Before sympathetics kick in, at about what pressure would we see the cerebral blood flow start to increase as the mean arterial blood pressure increases?
140 mmHg
What happens when the sympathetics are activated with the cerebral circulation?
the autoregulation is extended and the brain will vasoconstrict prior to the capillaries
As intracranial pressure goes up, what happens to the venous outflow?
it can compress the vein and collapse it,
what does a compressed/collapsed vein in the brain cause?
reduced arterial flow aka the brain suddenly doesn’t have enough blood flow and therefore less o2
What happens when a vein is compressed/ collapses in the brain?
the brain will activate the cardiovascular control centers in the medulla and increase systemic BP, sometimes drastically–> trying to force open the vein so blood can get through
What could increase the intracranial pressure?
hydrocephalus (Increased CSF), cerebral edema, intracranial bleeding, tumor
How is the lateral ventricles connected to the third ventricle?
intraventricular foramen
how is the 3rd ventricle connected to the 4th ventricle?
cerebral aquaduct
how is the 4th. ventricle connected to the cisterna magna?
median aperture
how is the 4th ventricle connected to the arachnoid space?
lateral apertures
What is the first step in the production of CSF?
filtration of serum
The filtration of serum is driven by what two pressures?
hydrostatic pressure and oncotic pressure
There are two types of hydrostatic pressure what are they?
there is one in the capillary (pushed fluid out) and a small one surrounding the capillary (pushes fluid into the capillary)
At the choroid plexus, what could be said about the oncotic pressure inside the capillary and surrounding the capillary?
they are equal and opposite so they cancel each other out
What is the 2nd step of the production of CSF?
modification of the ion composition in the CSF
What ions have equal concentrations in both the plasma and the CSF?
Na+ and HCO3
what is the significance of HCO3 in CSF?
it is critical for controlling the pH of CSF
What ions are found to have higher concentrations in the CSF compared to the plasma?
Mg2+ and Cl- and Co2
what is the increased CO2 in the CSF caused from?
neuronal metabolism
what ions are found to have a smaller concentration in the CSF when compared to the plasma?
K+, Ca2+, protein, and glucose
how is CSF reabsorbed?
by the arachnoid villi
at what pressures will the CSF not be absorbed by the arachnoid villi?
at pressures below 68 mmCSF
what is the normal pressure in the brain?
112 mm CSF
Capillaries in the brain have two components that limit exchange. What are they?
tight junctions between endothelial cells and glial end feet that come into close contact with the blood vessel
What are the four substances that absolutely need to cross the BBB?
H2O, CO2, O2, and free steroid hormones
how does H2O cross the BBB?
via a AQP 4 channel
how does CO2 get out of the CSF?
it is lipid soluble
how does O2 move from the blood vessel into the neuron?
it is lipid soluble
How does glucose cross the endothelial cell?
the 55 K Glut 1 transporter
How does glucose cross the glial end foot?
the 45 K Glut 1 transporter
How does glucose get into the neuron?
using the Glut 3 transporter
What is present in the CSF that keeps the composition of ions in check?
the Na/K/2Cl transporter
How is the expression of the Na/K/2Cl transporter controlled?
by the release of two peptides released from the endothelial cells of the blood vessels–> endothelin 1 and endothelin 3
There are a lot of drugs and chemical that still cross the BBB. How does the brain account for this?
those drugs are moved back to the blood via p-glycoprotein (MDR-1)
the maintenance of the electrolyte composition is particularly related to what ion?
K+
What does it mean when we say we are going to handicap the BBB?
in the 4 regions that need it, the capillaries do not have tight junctions between the endothelial cells
What are the four circumventricular organs?
the posterior pituitary, the area postrema, the OVLT, and the subfornical organ
why does the posterior pituitary need access to the blood?
it releases hormones into the blood
why does the area postrema need access to the blood?
it induces vomiting as a protection mechanism if there is a toxin in the blood
why do the OVLT and subfornical organ need access to the blood?
they both control water/ thirst/ and blood volume control
what is the significance of the sympathetics causing vasoconstriction to happen prior to the capillaries?
it will increase the systemic vascular resistance but it protects the capillaries in the brain and the BBB from damage
What is the net result of the first step of CSF production?
the hydrostatic pressure in the capillary dominates everything and pushes water out into the ventricle
