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
2024-01-12
26
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] According to the passage, an injection of insulin was most similar in its effect on rats to an injection of
选项
A、tyrosine.
B、leucine.
C、blood.
D、tryptophan.
E、protein.
答案
D
解析
给老鼠打一针胰岛素,相当于给它打一针:文中胰岛素、色氨酸都是促进血清素分泌的。∴D正确。色氨酸。
转载请注明原文地址:https://tihaiku.com/zcyy/3357423.html
相关试题推荐
Themetabolicrateofsharksislowcomparedwiththeratesofmostotherfishes
ThepsychologistWilliamJamesbelievedthatfacialexpressionsnotonlyprovide
Inthe1950’sastronomersweredividedbetweenthosewhobelievedtheuniverseb
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Untilrecentlymostastronomersbelievedthatthespacebetweenthegalaxies
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
Itwasoncebelievedthatthebrainwasindependentofmetabolicprocesseso
随机试题
Whichofthefollowingstatementsisthebesttitleforthepassage?[originalte
Workersinbigfirmsreceiveasubstantialpartoftheirpayintheformof____
JusticeDepartment’sdecisiontofireitseightemployeeshas______.[originalte
[originaltext]Cleanairisimportanttogoodhealth.Iftheaircontainsim
Forthispart,youareallowed30minutestowriteashortessayentitledCr
与意志的自制力相反的品质是()A.受暗示性 B.优柔寡断 C.执拗 D.
下列出版专业技术职务中,属于中级职务的是()。A.一级校对 B.技术设计员
谈到大数据时,有一则故事经常被引用:一位男顾客到一家连锁店投诉,因为该店竟然给他
己知某基础面积A=4X2m2,埋深h=1.5m,外加荷载F=900kN,地
()是社会经济制度变革的根本原因。A.生产力的发展 B.生产关系的变化 C.
最新回复
(
0
)