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您请求的操作仅限于组中的用户:==天然屏障== #[[皮肤]]#*通常阻止入侵的微生物,除非它被物理破坏(例如,由节肢动物载体,损伤,静脉导管,手术切口)。许多粘膜浸没在具有抗菌特性的分泌物中(例如,宫颈粘液、前列腺液和含有溶菌酶的泪液,溶菌酶可分裂细菌细胞壁中的乳杆菌酸链,特别是在革兰氏阳性生物体中)。局部分泌物还含有免疫球蛋白,主要是IgG和分泌性IgA,它们可以防止微生物附着在宿主细胞上,以及结合铁的蛋白质,铁对许多微生物都是必需的。如果入侵的微生物到达气管支气管树,纤毛粘膜上皮将它们从[[肺解剖|肺]]运送出去。咳嗽也有助于清除细菌。如果微生物到达肺泡,肺泡巨噬细胞和组织组织细胞将它们吞噬。这些防御可以被大量生物体、空气污染物(如香烟烟雾)、对保护机制的干扰(如气管内插管、气管造口术)或先天缺陷(如囊性纤维化|囊性纤维化)所克服。胃肠道屏障包括胃酸的pH值和胰腺酶、胆汁和肠道分泌物的抗菌活性。#*蠕动和上皮细胞的正常丢失会清除微生物。如果蠕动减慢(例如,由于颠茄或鸦片生物碱等药物),这种清除被延迟并延长某些感染,例如症状性志贺氏菌病。 #* Compromised GI defense mechanisms may predispose patients to particular infections (eg, achlorhydria predisposes to salmonellosis). #* Normal bowel flora can inhibit pathogens - alteration of this flora with antibiotics can allow overgrowth of inherently pathogenic microorganisms. #GU tract #* Barriers include the length of the urethra (20 cm) in men, the acid pH of the vagina in women, the hypertonic state of the kidney medulla, and the urine urea concentration. #* The kidneys also produce and excrete large amounts of Tamm-Horsfall mucoprotein, which binds certain bacteria, facilitating their harmless removal.Merck Manuals Professional Version. Host Defense Mechanisms Against Infection. http://www.merckmanuals.com/professional/infectious-diseases/biology-of-infectious-disease/host-defense-mechanisms-against-infection. (Last Accessed: 19.6.2020)

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