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26 Cards in this Set

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  • Back
if cerebral bloodflow is inhibited, how long will it take to lose consciousness? have irreversible damage?
10 seconds. 3-5 minutes
circulation through the brain depends upon what?
perfusion pressure (difference between mean arterial pressure and the intracranial pressure) and the resistance to flow.
what is the functional perfusion pressure of the brain?
the mean arterial blood pressure, but under certain pathological conditions, the venous pressure and the intracranial pressure may raise, thus reducing the effective perfusion pressure
cerebrovascular resistance depends upon what factors? what about functionally?
viscosity of blood and vascular factors such as vessel diameter, length, and number of connecting vessels. functionally only the diameter of the vessels matter
autoregulation keeps a constant CBF as long as the mean blood pressure does not drop to what? how does it accomplish this?
60 mmHg or less, it accomplishes this by dilating the blood vessels in the brain over various BP ranges.
when the blood pressure is too high, what does autoregulation do?
constricts vessels to regulate CBF
autoregulation of CBF is important for protection from and against what?
against extracranial cerebrovascular disease, increased intracranial pressure, and decreased cardiac output. protection from changes in perfusion pressure due to changes in body posture
physiologically, what is the major regulator of CBF?
pCO2 in blood and cerebral tissues
increased pCO2 will do what to the CBF?
increase it via vasodilation
how do temperature and oxygen affect CBF?
not as much as CO2 does, but increasing PO2 generally decreases CBF and vice versa, while significantly increasing temp will increase CBF and vice versa
cerebral vein blood is what compared to the bulk of venous blood
less oxygenated
oxygen to the brain is primarilly used for what?
synthesis of ATP, the brain cannot perform anaerobic metabolism like most other organs
does oxygen demand of the brain ever change?
no, not even during sleep
high energy consumption of the brain seems to be related to what?
transport of ions to maintain electrical potentials, synthesize NT, enzyme replacement, and structural replacement
what is the energy equation for the brain?
glucose + O2 -> CO2, H2O, pyruvate and lactate
the glucose dependence of the CNS is due to what?
the blood brain barrier will not allow other substances in, not from an inability of the neural tissue to metabolize other things
what does the brain do in states of hypoglycemia?
it uses any available free glucose, then switches to the small amount of stored, slow moving glycogen stored in the glia. free amino acids are used next (especially aspartate and glutamate). Finally protein and lipid are degraded, but by this time irreversible damage will have occured.
what is insulin's effect on the brain in terms of glucose uptake?
none, but if hypoglycemia is due to increased insulin, the brain must compete with the muscles and liver for the glucose, thus intensifying the problem
cerebral metabolic rate will fall when what occurs?
brain function is impaired, before the metabolic rate is reduced by half, a coma will ensue
how can seizures cause brain damage?
the high energy demand of all those firing neurons complicated by possible ischemia due to lack of respiration leads to depletion of energy from the brain
what compound can be used as a partial substitute for glucose in the brain during periods of starvation and suckling?
ketone bodies
what molecule is used to image metabolism in humans for PET scans?
how do PET scans and autoradiograms of cerebral blood flow give an indication of metabolic activity?
autoregulation alters CBF in response to changes in local metabolism of tissues, BUT note that they do not correlate perfectly
locations of epileptic foci and tumors in the brain usually show what in terms of CBF and GU (glucose uptake)?
increases in both
give a clinically important example of when the small dissociation between GU and CBF is important?
dead tissue has no metabolic activity, but blood will flow through it, thus these levels maybe checked in damage heart tissue to determine the most appropriate surgery
how does BOLD fMRI work?
apparently when brain activity increases, GU increases, but O2 uptake from blood actually declines, thus there are reduced hemoglobin concentrations in veins draining metabolically active areas, and there is a magnetic difference between oxy hemoglobin and hemoglobin and this shows up on MRI