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Cerebral Blood Flow and Metabolism
N/A
36
Anatomy
Graduate
02/15/2012

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Cards

Term
Brain metabolism is based almost entirely on the oxidation of what?
Definition
Glucose oxidized to CO2
Term
Minor amounts of glucose are used in what processes?
Definition
Anaerobic glycolysis, production of glycoproteins and glycolipids, synthesis of neurotransmitters glutamate, GABA, and acetylcholine
Term
What is the majority (50-60%) of glucose metabolism used for in the brain?
Definition
Maintenance of membrane potentials, primarily via Na/K ATPase pumps
Term
Slightly less than half (~40%) of glucose metabolism has what function in the brain?
Definition
Basic cellular metabolism not related to functional activity
Term
What is the result of a disruption in glycolytic energy stores?
Definition
Slow depolarization of membranes bringing them closer to threshold, increasing sensitivity (leads to seizures)
Term
What cells form the major interface for metabolic processing of glucose in the brain?
Definition
Astrocytes
Term
How do astrocytes interact with glucose?
Definition
Responsible for the transfer of glucose from the blood to neurons, form the primary brain reservoir for glycogen
Term
What compound is used to monitor glucose uptake in the brain through the use of PET scans?
Definition
2-deoxyglucose labelled with 18-Flourine
Term
In the absence of glucose, what alternative metabolic precursor acts as a carbohydrate source that can be utilized for energy?
Definition
Mannose, though levels are usually low and it is absorbed slower than glucose
Term
Starvation, diabetes, and low carbohydrate diets may induce the use of what other alternative energy source?
Definition
Ketone bodies and free fatty acids from lipid metabolism, acetone is primary byproduct
Term
What stimulates the release of lactate at the synaptic junction by astrocytes?
Definition
Glutamate
Term
What is the primary regulator of cerebral blood flow?
Definition
Via tone of vascular smooth muscle controlled primarily by autoregulatory mechanisms and mediators (though there is some innervation as well)
Term
The majority (~2/3) of vascular resistance is attributed to what structures in cerebral blood flow?
Definition
Pial vessels via smooth muscle regulation
Term
The major homeostatic mechanisms regulating cerebral circulation are what?
Definition
Metabolic, myogenic, neurogenic
Term
Under normal circumstances, cerebral blood flow is directly coupled with what homeostatic mechanism?
Definition
Metabolism - increased neuronal activity is accompanied by vasodilation and increased blood flow via metabolic adenosine, NO, and CO2 levels
Term
NO modulates cerebral vessels particularly in the release of what neurotransmitter?
Definition
Glutamate
Term
Some autoregulatory mechanisms, particularly in intracerebral arterioles, are mediated by what cells?
Definition
Astrocytes via coupling through gap junctions and their cellular domains
Term
What is the most potent physiologic cerebral vasodilator, capable of initiating changes in seconds?
Definition
CO2 rapid crossing the blood-brain barrier
Term
Why does a rapid increase in CO2 cause vasodilation?
Definition
Reduction in pH of the perivascular fluid leads to vsodilation, possibly through NO and prostaglandin mediated mechanisms
Term
Hypercapnia means what?
Definition
Increased CO2 -> vessels dilate
Term
Hypocapnia means what?
Definition
Decreased CO2 -> vessels constrict
Term
How does the cerebral vessel response to increased oxygen (hypoxemia) differ from hypercapnia?
Definition
Much slower vasodilation response, is independent of baroreceptors and chemoreceptors
Term
The tight relationship between metabolism to blood flow (observable via MRI and other imaging methods) implies what relationship?
Definition
Blood flow increases reflect neural activity
Term
What is the primary myogenic mechanism that impacts cerebral blood flow?
Definition
Arterial blood pressure
Term
What is the most abundant perivascular neurotransmitter?
Definition
Acetylcholine
Term
What effect does hypothermia have on cerebral circulation?
Definition
Reduces cerebral oxygen metabolism and blood flow at a rate of 5-7% per degree Celsius.
Term
When is cerebral perfusion pressure regulated?
Definition
Never, except in cases of brain trauma, disease, or hypertension
Term
What is the anatomical basis for the blood brain barrier?
Definition
Capillary endothelial cells and their tight junctions, perviascular cells, a basement membrane, and astrocyte processes
Term
What is the most significant antomical basis for the blood brain barrier?
Definition
Capillary endothelial cells in brain tissue
Term
Who do capillaries found in the brain differ from capillaries seen elsewhere in the body?
Definition
Contains endothelial cells with tight junctions between them and much more restrictive system transport.
Term
What substances are freely allowed through the blood brain barrier?
Definition
Gases, lipid soluble substances, and water pass freely, electrolytes and glucose pass slowly and are often transport mediated
Term
What substances are barred from passed the blood brain barrier?
Definition
Plasma proteins and large organic molecules
Term
Why is the fetus or newborn susceptible to CNS effects of drugs that would not normally effect adults?
Definition
Blood brain barrier is not fully developed
Term
What factors are capable of altering the blood brain barrier?
Definition
Direct trauma, chemical toxins, tumors, severe hypertension, sever hypercapnia
Term
What are the consequences of a disrupted blood brain barrier?
Definition
Cerebral edema, disrupted ionic balance, may require slow functional recovery
Term
Do brain tumors have a blood brain barrier?
Definition
Frequently do not, though slow growing tumors may keep it intact
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