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