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
考研
The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune
The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune
admin
2020-01-09
117
问题
The immune system is equal in complexity to the combined intricacies of the brain and nervous system. The success of the immune system in defending the body relies on a dynamic regulatory communications network consisting of millions and millions of cells. Organized into sets and subsets, these cells pass information back and forth like clouds of bees swarming around a hive. The result is a sensitive system of checks and balances that produces an immune response that is prompt, appropriate, effective, and self-limiting.
At the heart of the immune system is the ability to distinguish between self and non-self. When immune defenders encounter cells or organisms carrying foreign or non-self molecules, the immune troops move quickly to eliminate the intruders. Virtually every body cell carries distinctive molecules that identify it as self. The body’s immune defenses do not normally attack tissues that carry a self-marker. Rather , immune cells and other body cells coexist peaceably in a state known as self-tolerance. When a normally functioning immune system attacks a non-self molecule, the system has the ability to remember the specifics of the foreign body. Upon subsequent encounters with the same species of molecules, the immune system reacts accordingly. With the possible exception of antibodies passed during lactation, this so-called immune system memory is not inherited. Despite the occurrence of a virus in your family, your immune system must learn from experience with the many millions of distinctive non-self molecules in the sea of microbes in which we live. Learning entails producing the appropriate molecules and cells to match up with and counteract each non-self invader.
Any substance capable of triggering an immune response is called an antigen. Antigens are not to be confused with allergens, which are most often harmless substances ( such as ragweed pollen or cat hair) that provoke the immune system to set off the inappropriate and harmful response known as allergy. An antigen can be a virus, a bacterium, a fungus, a parasite, or even a portion or product of one of these organisms. Tissues or cells from another individual (except an identical twin, whose cells carry identical selfmarkers) also act as antigens; because the immune system recognizes transplanted tissues as foreign, it rejects them. The body will even reject nourishing proteins unless they are first broken down by the digestive system into their primary, non-antigenic building blocks. An antigen announces its foreignness by means of intricate and characteristic shapes called epitopes, which protrude from its surface. Most antigens, even the simplest microbes, carry several different kinds of epitopes on their surface; some may even carry several hundred. Some epitopes will be more effective than others at stimulating an immune response. Only in abnormal situations does the immune system wrongly identify self as non-self and execute a misdirected immune attack. The result can be a so-called autoimmune disease such as rheumatoid arthritis or systemic lupus erythematosis. The painful side effects of these diseases are caused by a person’s immune system actually attacking itself.
Which of the following best expresses the main idea of this passage?
选项
A、An antigen is any substance that triggers an immune response.
B、The basic function of the immune system is to distinguish between self and non-self.
C、One of the immune system’s primary functions is the allergic response.
D、The human body presents an opportune habitat for microbes.
答案
B
解析
主旨题。全文第一段引出了免疫系统的工作原理,并在第二段主要讨论了该系统如何区分自身细胞和外来细胞这一能力,在最后一段重点阐述了免疫功能中抗原的活动情况。因此,正确答案是[B]。选项[A][C][D]在文中均有涉及,但并非全文围绕的中心话题。
转载请注明原文地址:https://kaotiyun.com/show/X7e4777K
0
考研英语二
相关试题推荐
Geneticengineeringholdsgreatpotentialpayoffsforfarmersandconsumersbymakingcropsresistanttopests,diseases,andev
Howcanacompanyimproveitssales?Oneofthekeystomoreeffectivesellingisforacompanytofirstdecideonits"salesst
Einstein,likeothergreatphysicistsbeforehim,workedoutnewtheoriesthatchallengeour______conceptoftheuniverse.
EveryspringmigratingsalmonreturntoBritishColumbia’sriverstospawn.Andeveryspringnewreportsdetailfreshdisasters
WholesalepricesinJulyrosemoresharplythanexpectedandatafasterratethanconsumerprices,【1】thatbusinesseswerestill
WholesalepricesinJulyrosemoresharplythanexpectedandatafasterratethanconsumerprices,【1】thatbusinesseswerestill
WilltheEuropeanUnionmakeit?Thequestionwouldhavesoundedstrangenotlongago.Noweventheproject’sgreatestcheerlead
In1999,thepriceofoilhoveredaround$16abarrel.By2008,ithad【1】the$100abarrelmark.Thereasonsforthesurge【2】fro
Scientistsoftenstruggletocommunicatethefindingsofresearch.Oursubjectmattercanbetechnicalandnoteasilydigestedb
随机试题
以企业产品商标或服务商标为对象所实施的战略是()
这上面的夜的天空,奇怪而高,我生平没有见过这样的奇怪而高的天空。他仿佛要离开人间而去,使人们仰面不再看见。然而现在却非常之蓝,闪闪地目夹着几十个星星的眼,冷眼。他的口角上现出微笑,似乎自以为大有深意,而将繁霜洒在我的园里的野花草上。这里主要采用了什么修
确定糖苷中糖的连接位置,可采用将糖苷进行
降低退票费是惠民之举,铁路部门的确走出了一大步,但铁路部门不必过分和过早期待公众的欢呼。降低退票费,与公众对铁路部门期待还有很远的差距。公众不会满足于退票费的降低,他们希望的是垄断部门能够狠下心来废除一切貌似合理的收费。当这种诉求不再成为奢望,人们自然会热
按照服务内容的不同,物流服务项目可分为()。
某业主与某施工单位签订了施工总承包合同,该工程采用边设计边施工的方式进行,合同的部分条款如下:××工程施工合同书(节选)一、协议书(一)工程概况
五笔字型输入法属于()。
2006年实际建设占用耕地占当年实际减少耕地的比重是()。全年总用水量占全年水资源总量的比重是()。
单击命令按钮时,下列的执行结果为 PrivateSubCommand1_Click() DimxAsInteger,yAsInteger x=86:y=29 CallProc(x,y) Printx;y End
要使标签中的文本靠右显示,应将其Aligment属性设置为
最新回复
(
0
)