首页
登录
职称英语
It was once believed that the brain was independent of metabolic processes o
It was once believed that the brain was independent of metabolic processes o
游客
2025-02-25
9
管理
问题
It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discov- ered that the production and release in brain neurons of the neurotransmitter serotonin(neurotransmitters are compounds that neurons use to transmit signals to other cells)depend directly on the food that the body processes.
Our first studies sought to determine whether the increase in serotonin observed in rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled with blood-tryp-tophan increases. In later studies we found that injecting insulin into a rat’s bloodstream also caused parallel elevations in blood and brain tryptophan levels and in serotonin levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood trypto- phan level and the concentrations of tryptophan serotonin in the brain increased after the meal.
Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell. Since protein contains tryptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryp- tophan to the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood con- centration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein in the meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided to the brain. Thus the more protein in a meal, the less serotonin subsequently produced and re- leased. [br] The authors’ discussion of the "mechanism that provides blood tryptophan to the brain cells"(lines 44-45)is meant to
选项
A、stimulate further research studies.
B、summarize an area of scientific investigation.
C、help explain why a particular research finding was obtained.
D、provide supporting evidence for a controversial scientific theory.
E、refute the conclusions of a previously mentioned research study.
答案
C
解析
作者为什么要讨论“色氨酸进入脑细胞的机制”?A.激励继续研究。无。B.总结科学研究。无。C.正确。解释为何会有一特殊观测结果。这一特殊结果即第三段一开始surprisingly的内容。D.支持一有争议论点。无。E.驳斥一个前面的研究结论。第三段举一特例并不是为了将前面观点驳倒,只是给一个补充说明而已。
转载请注明原文地址:https://tihaiku.com/zcyy/3971984.html
相关试题推荐
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
LinandMarkeachattemptindependentlytodecodeamessage.Iftheprobability
Inaprobabilityexperiment,GandHareindependentevents.Theprobabilitytha
Inaprobabilityexperiment,GandHareindependentevents.Theprobabilitytha
A、provingthatthermoregulationistheprimarymeansbywhichmetabolicratesar
HAPLESS:A、guaranteedB、entirelyindependentC、eagerD、fortunateE、elatedD
随机试题
WhichofthefollowingitalicizedpartsindicatesaCAUSE?A、Hesucceededbyhard
Well-to-doparentsareincreasinglyoptingtosendtheirchildrentosingle-
Outof________revenge,hedidhisworsttoblackenhercharacterandruinher
ThecityfinallywonapprovalforalimitedspeedcameraprograminJuneaft
(2016年)证实银行存款期末余额是否真实存在,审计人员可以实施的审计程序有:A
在建筑材料的力学性质中,处于一对相反性质的是下面所列选项中的()。A.抗拉
(2017年11月)()是当人们生病或受到伤害后,由国家或社会提供医疗服务或经
迎送悲欢多少事,悠悠渡水几今朝。古城苏州,向来不缺尘封的________故事,再
A.腹水为漏出液 B.腹水为血液 C.腹水介于渗出液与漏出液之间 D.腹水
(2021年真题第2批)施工变更是指( )由双方当事人依法对合同内容所进行的修
最新回复
(
0
)