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
52
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
WhentheAmericaneconomywasrunningfulltilttwoyearsago,fewplaceswereasbreathlesslydelightedasSeattle.Itsportwa
Youshouldn’thavewritteninthe______sincethebookbelongstothelibrary.
Overthepastdecade,manycompanieshadperfectedtheartofcreatingautomaticbehaviors-habits-amongconsumers.Thesehabits
WholesalepricesinJulyrosemoresharplythanexpectedandatafasterratethanconsumerprices,【1】thatbusinesseswerestill
WholesalepricesinJulyrosemoresharplythanexpectedandatafasterratethanconsumerprices,【1】thatbusinesseswerestill
Readthefollowingtextandanswerquestionsbyfindinginformationfromtherightcolumnthatcorrespondstoeachofthemarked
In1999,thepriceofoilhoveredaround$16abarrel.By2008,ithad【1】the$100abarrelmark.Thereasonsforthesurge【2】fro
Thebattletopreventoratleastslowglobalwarminghasintensifiedinthepastyearasscientistshavelearnedmoreaboutthe
Runningmaybethesinglemosteffectiveexercisetoincreaselifeexpectancy,accordingtoanewreviewandanalysisofpastre
随机试题
张某,女,男性,62岁,于3年前长一小肿块,没有在意,近1年肿物渐大,质软,并伴有心悸、心烦,失眠易出汗,偶尔有手指颤动,眼睛干涩,身体疲倦,舌质红,偶有舌体颤动,脉弦数。
患者男,35岁。因左上前牙反复肿胀、疼痛6个月,加重1周人院。查体见左上颌前庭沟丰满,可扪及乒乓球样感,有轻压痛。左、右上颌中切牙、左上侧切牙及尖牙I~Ⅱ度松动,变色。硬腭部未见膨隆。影像学结合临床诊断为左上颌肿物,需行口内进路肿物摘除术。术后患者术区
()属于不得认定为工伤或者视同工伤。
政府财务会计应准确完整反映政府预算收入、预算支出和预算结余等预算执行信息。()
下列说法不正确的有()。
下列关于社会政策的对象描述正确的是()。
罗杰斯的“以学生为本”“让学生自发学习”“排除对学习者自身的威胁”的教学原则属于()(济宁高新)
Ⅳ个进程共享M台打印机(其中N>M),假设每台打印机为临界资源,必须独占使用,则打印机的互斥信号量的取值范围为()。
求下列极限:[*]【*】
一副扑克牌(去掉2张王牌),每人随意摸2张牌,至少有多少人才能保证他们当中一定有两个人所摸2张牌的花色情况是相同的?
最新回复
(
0
)