首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Importance of Vitamins Vitamins, which come in many different types all of which are quite diverse in chemical configuration
Importance of Vitamins Vitamins, which come in many different types all of which are quite diverse in chemical configuration
admin
2011-01-15
20
问题
Importance of Vitamins
Vitamins, which come in many different types all of which are quite diverse in chemical configuration and function, can be any of several organic substances that are separated into water-soluble and fat-soluble groups. Originally defined as organic compounds obtainable in a normal diet and capable of maintaining life and promoting growth, vitamins are differrent from carbohydrates, fats, and proteins in function, as well as in the quantities in which organisms require them. So critical are vitamins to a body’s essential strength and health that if they are absent from the diet or not properly absorbed by an organism, a specific deficiency disease may develop.
The term vitamin originated from "vitamine," a word first used in the early 19th century to designate a group of compounds considered vital for life (though the term "accessory food factor" sometimes is used interchangeably to refer to these substances). Like other nutrients, vitamin consumption is imperative to keep our bodies functioning properly, and if there is a lack of vitamin consumption, the body will fail to react in a way that’s considered healthy. Lack of vitamin A will result in various disorders that most commonly involve the eye and the tissues around it. One of the earliest symptoms of vitamin A deficiency is nyctalopia, the medical term for night blindness, which causes a visual failure to adapt quickly from light to darkness and an inability to see in the dark. This aspect of vision is normally dependent on rhodopsin, a protein found in the eye that maintains itself only in the presence of vitamin A; in the lack of vitamin A, rhodopsin will malfunction.
These earlier symptoms are quite harmless but the side effects can become increasingly serious if not treated early on. If the deficiency is severe and persists, especially in malnourished infants and children, a condition known as xerophthalmia--when the eyes are sensitive to light, the secretion of lubricating tears is stopped, and the eyelids become swollen and develop pus -- may develop. Furthermore, the mucous surfaces of the eye may become eroded, allowing infection to set in, thus leading to ulceration and other destructive changes of the cornea and other structures of the eye, resulting eventually in blindness.
A Early signs of vitamin A deficiency may also be reflected in changes in the membranes of the mouth, throat, and respiratory and genito-urinary passages where the lining membranes become malnourished and dry and lose their cilia, the tiny hairlike projections that normally help in clearing away foreign particles. B The natural immune system is weakened and if insufficient intake of vitamin A is prolonged, the skin may become dry and rough. C Vitamin A deficiency may also result in defective bone and teeth formation and in poor general growth.D
However, an excessive intake of vitamin A can also cause severe damages to the body causing a symptom called "hypervitaminosis A", which happens when a person takes in more than 150 milligrams of vitamin A over a long period of time; the vitamins are stored in the liver and can reach dangerous level because the A vitamins are not employed to make the bodies stronger, but rather, stored as toxic material. Excessive amounts of vitamin A can cause nausea, dryness of skin, blurred vision, drowsiness, and bone pain.
Vitamin A can be found in all animal livers, in milk products, and in many yellow and green leafy vegetables which contain carotenes, chemically related substances that are converted to vitamin A in the body. There are various other vitamins that the human body needs in order to survive; the excessive intake of vitamin A, or the lack of intake of other vitamins, causes detriment to the human body--at all times, moderation is key.
According to the paragraph 4, which of the following is true of cilia?
选项
A、Cilia are tiny extensions of membranes that normally provide help in clearing the membranes.
B、The term "cilia" refers to the hair lining of membranes that prevent foreign matter from entering our body.
C、The tiny projections in the lining membranes are known as cilia and they block incoming foreign matters.
D、Cilia are part of the lining membranes of the mouth and throat, and they help preventing external particles from entering our body.
答案
C
解析
转载请注明原文地址:https://jikaoti.com/ti/m8lYFFFM
0
托福(TOEFL)
相关试题推荐
MorseCodeMorsecodeisbeingreplacedbyanewsatellite-basedsystemforsendingdistresscallsatsea.Itsdotsanddashesh
MorseCodeMorsecodeisbeingreplacedbyanewsatellite-basedsystemforsendingdistresscallsatsea.Itsdotsanddashesh
ClassifythefollowinginformationasreferringtoAadoptedthewritingsystemfromanothercountryBusedorganicmaterialst
Inthelastdecadearevolutionhasoccurredinthewaythatscientiststhinkaboutthebrain.Wenowknowthatthedecisionshu
TheEvolutionaryMystery:CrocodileSurvivesA.Eventhoughcrocodileshaveexistedfor200millionyears,they’reanything
Theuniversityhasproduceda______toinformstudentsaboutthedifferentaccommodationoptionsavailable.SperrinHalls
Theuniversityhasproduceda______toinformstudentsaboutthedifferentaccommodationoptionsavailable.Thisisthemoste
Theuniversityhasproduceda______toinformstudentsaboutthedifferentaccommodationoptionsavailable.Mealsareincluded
Atthestartofthetutorial,thetutoremphasisestheimportanceof【25】
随机试题
对蛛网膜下腔出血病因的诊断,最有意义的辅助检查是
完成估价报告后,应及时将估价报告交付给()。
如图7-8所示,两电路相互等效,由图(b)可知,流经10Ω电阻的电流IR=1A,由此可求得流经图(a)电路中10Ω电阻的电流I等于()。
统计推断的方法主要包括()。I.参数估计Ⅱ.假设检验Ⅲ.线性回归Ⅳ.逻辑推理
不属于银行内部资源分析的研究开发分析的是()。
下列关于我国资本市场B股的说法中,正确的是()。
1965年,美国测验专家伊贝尔(L.Ebel)根据长期的经验提出用鉴别指数评价项目性能的标准,鉴别指数D为(),说明该项目差,必须淘汰。
“勤学如春起之苗,不见其增,日有所长;辍学如磨刀之石,不见其损,年有所亏。”下列与此反映的哲理相似的是()
(1)确定目标市场(2)数据分析(3)针对性修改产品包装(4)产品上市(5)市场调查
乡、民族乡、镇的国家机构分为()。
最新回复
(
0
)