Defence Against Disease | 抵抗疾病的防御机制

📚 Defence Against Disease | 抵抗疾病的防御机制

The human body is constantly exposed to pathogens, including bacteria, viruses, fungi and protists. Disease occurs when a pathogen enters the body, multiplies and causes damage. The immune system provides a multi-layered defence that can be divided into non-specific and specific responses. This article summarises the key concepts required for Cambridge A-Level Biology.

人体持续暴露于细菌、病毒、真菌和原生生物等病原体。当病原体进入人体、繁殖并造成损害时，疾病就会发生。免疫系统提供多层次的防御，可分为非特异性应答和特异性应答。本文总结了剑桥A-Level生物课程需要掌握的关键概念。

1. Introduction to Defence Systems | 防御系统概述

Defence mechanisms are broadly classified into non-specific (innate) and specific (adaptive) immunity. Non-specific defences act immediately against any pathogen, whereas specific defences are slower but target particular antigens. The two systems work together to prevent infection and to destroy pathogens that have entered the body.

防御机制大致分为非特异性（先天）免疫和特异性（适应性）免疫。非特异性防御立即对任何病原体起作用，而特异性防御虽然较慢，但针对特定抗原。两个系统协同工作，以预防感染并消灭已进入体内的病原体。

Key barriers include physical, chemical and cellular components. The first line of defence includes the skin and mucous membranes, while the second line includes phagocytes, inflammation and antimicrobial proteins. Specific immunity involves lymphocytes known as B cells and T cells.

关键屏障包括物理、化学和细胞成分。第一道防线包括皮肤和黏膜，第二道防线包括吞噬细胞、炎症和抗菌蛋白。特异性免疫涉及称为B细胞和T细胞的淋巴细胞。

2. Non-Specific Barriers: Skin and Mucous Membranes | 非特异性屏障：皮肤和黏膜

The skin is the largest organ and provides an effective physical barrier. Its outer layer, the epidermis, is made of tightly packed keratinised cells that are difficult for pathogens to penetrate. Sebum secreted by sebaceous glands contains fatty acids that lower pH and inhibit microbial growth.

皮肤是最大的器官，提供有效的物理屏障。表皮外层由紧密排列的角质化细胞组成，病原体难以穿透。皮脂腺分泌的皮脂含有脂肪酸，可降低pH并抑制微生物生长。

Mucous membranes line the respiratory, digestive and reproductive tracts. They secrete sticky mucus that traps pathogens. Ciliated epithelial cells in the trachea move mucus upwards towards the throat, where it is swallowed or coughed out. In the stomach, hydrochloric acid destroys many pathogens.

黏膜覆盖呼吸道、消化道和生殖道内表面。它们分泌黏稠的黏液以捕获病原体。气管中的纤毛上皮细胞将黏液向上推向咽喉，然后被吞咽或咳出。在胃中，盐酸可杀死许多病原体。

Chemical defences include lysozyme, an enzyme found in tears, saliva and sweat that breaks down bacterial cell walls. In addition, normal flora on the skin and gut compete with pathogens for space and nutrients, acting as a further biological barrier.

化学防御包括溶菌酶，这是一种存在于泪液、唾液和汗液中的酶，可破坏细菌细胞壁。此外，皮肤和肠道中的正常菌群与病原体竞争空间和营养物质，形成进一步的生物屏障。

3. Phagocytosis and Inflammation | 吞噬作用和炎症

If pathogens breach the first line of defence, phagocytes such as neutrophils and macrophages carry out phagocytosis. The phagocyte recognises the pathogen, engulfs it by endocytosis, and encloses it in a phagosome. Lysosomes fuse with the phagosome to form a phagolysosome, where digestive enzymes and reactive oxygen species destroy the pathogen.

如果病原体突破第一道防线，中性粒细胞和巨噬细胞等吞噬细胞会进行吞噬作用。吞噬细胞识别病原体，通过内吞将其包裹，并封入吞噬体。溶酶体与吞噬体融合形成吞噬溶酶体，其中的消化酶和活性氧物质将病原体消灭。

Inflammation is a local response to tissue damage or infection. Damaged mast cells release histamine, which causes vasodilation and increases capillary permeability. This results in redness, heat, swelling and pain. Increased blood flow delivers more phagocytes to the infected area.

炎症是对组织损伤或感染的局部反应。受损的肥大细胞释放组胺，引起血管扩张并增加毛细血管通透性。这导致红、热、肿、痛。血流增加将更多吞噬细胞运送到感染区域。

Cytokines and other signalling molecules attract phagocytes by chemotaxis. If a pathogen enters a cell, that cell may release interferons, which diffuse to neighbouring cells and make them more resistant to viral replication. These responses are still non-specific.

细胞因子和其他信号分子通过趋化作用吸引吞噬细胞。如果病原体进入细胞，该细胞可能释放干扰素，干扰素扩散

Published by TutorHao | A-Level Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）