什么是免疫系统
身体细胞、细胞产物、器官及构造,察觉与摧毁外来入侵的细菌、病毒及癌细胞。免疫力是基於系统发动对抗入侵者的防卫能力。要让系统运作正常,必须能够分辨身体自己的物质(自身)和外界来源的物质(非自身)。分辨失效会造成自体免疫疾病,免疫系统对没有害处的物质(如花粉、动物皮屑)产生过大或不适当的反应,会造成过敏。系统主要细胞像是辨别抗原的淋巴球,以相关的附属细胞(如巨噬细胞将外来物质吞掉并杀死)。淋巴球是在骨髓从干细胞产生,T淋巴球(T细胞)移动到胸腺而成熟,B淋巴球(B细胞)则是在骨髓中成熟。成熟的淋巴球进入血流,许多与附属细胞寄宿在身体各种组织之中,包括脾脏、淋巴结、扁桃腺及肠黏膜。在这些器官和组织之内,淋巴球受限於结缔组织的纤细网状系统,四处输送去接触抗原。T细胞与B细胞受到适当的刺激,会在淋巴组织进一步成熟与倍增繁殖。淋巴组织排出的体液(淋巴液)透过淋巴管搬运到血液。淋巴结沿着淋巴管分布,过滤淋巴,找出里面所含的巨噬细胞和淋巴球有无抗原存在。脾脏有类似的功能,抽取血样检查有无抗原。淋巴球可以在淋巴组织、血液与淋巴之间穿梭,是免疫系统机能的重要元素。亦请参阅immunodeficiency、immunology。
immune system
Cells, cell products, organs, and structures of the body involved in the detection and destruction of foreign invaders, such as bacteria, viruses, and cancer cells. Immunity is based on the system's ability to launch a defense against such invaders. For the system to function properly, it must be able to distinguish between the material of its own body (self) and material that originates outside of it (nonself). Failure to make this distinction can result in autoimmune diseases. An exaggerated or inappropriate response by the immune system to nonharmful substances (e.g., pollen, animal dander) can result in allergies. The system's principal cells include lymphocytes that recognize antigens, and related accessory cells (such as phagocytic macrophages, which engulf and destroy foreign material). Lymphocytes arise in the bone marrow from stem cells with T lymphocytes (T cells) migrating to the thymus to mature and B lymphocytes (B cells) maturing in the bone marrow. Mature lymphocytes enter the bloodstream, and many become lodged, along with accessory cells, in various body tissues, including the spleen, lymph nodes, tonsils, and intestinal lining. Organs or tissues containing such concentrations are termed lymphoid. Within these organs and tissues the lymphocytes are confined within a delicate network of connective tissue that channels them so they come into contact with antigens. T cells and B cells can mature and multiply further in lymphoid tissue when suitably stimulated. Fluid (lymph) draining from lymphoid tissues is conveyed to the blood through lymphatic vessels. Lymph nodes distributed along these vessels filter the lymph, exposing macrophages and lymphocytes contained within to any antigen present. The spleen plays a similar role, sampling the blood for the presence of antigens. The capability of lymphocytes to pass between lymphoid tissue, the blood, and lymph is an important element in the system's functioning. See also immunodeficiency, immunology.
-
什么是D-葡萄糖醇
又称L-山梨糖醇、L-古罗糖醇。为D-葡萄糖分子中的羰基还原而得的糖醇,分子式C6H14O6。广泛存在于蔷薇科属水果(梨、苹果、桃、杏等)中,这些新鲜水果通常含有D-葡萄糖醇5%~10%。此外,红藻含有D-葡萄糖醇13.6%(干重)。在生物体内它是D-葡萄糖和D-果糖之间酶促相互转化的重...
-
什么是威海市
山东省港口城市,省辖市,中国海防要地之一。位于胶东半岛东北端,三面环山,一面临海,港湾内水域广阔,外有刘公岛屏蔽,地势险要。辖1区及乳山县。面积5436平方公里,人口237.46万;其中市区面积408平方公里,人口25.74万。威海城区在明以前,为海滨渔村。汉称石落村。元改称清泉...
-
什么是阜平县
河北省保定地区辖县。抗日革命根据地之一。位于省境中部太行山东麓。面积2480平方公里,人口19.04万。县府驻阜平镇。金明昌四年(1193)始置阜平,治所在今县城。清康熙年间曾移治所王快,后移今治所。县境位于山区,山地约占3/4,山高坡陡,地势险峻,大部海拔千米以上,最高峰...
-
什么是再发新星
爆发变星的一种。一般认为再发新星和新星之间并没有严格的区别,只是有的新星在第一次爆发之后,经过数年或数十年,又发生第二次、第三次甚至更多次的爆发,所以就称这种新星为再发新星。按一般分类法划分的再发新星已发现十二颗。再发新星在银河系中的分布与新星相似...