The mucosa of the gastrointestinal tract, eyes, nose, lungs, cervix and vagina is lined by epithelium interspersed with mucus-secreting goblet cells, all of which contribute to their unique functions. This mucus provides an integral defence to the epithelium against noxious agents and pathogens. However, it can equally act as a barrier to drugs and delivery systems targeting epithelial passive and active transport mechanisms. This review highlights the various mucins expressed at different mucosal surfaces on the human body, and their role in creating a mucoid architecture to protect epithelia with specialized functions. Various factors compromising the barrier properties of mucus have been discussed, with an emphasis on how disease states and microbiota can alter the physical properties of mucus. For instance, Akkermansia muciniphila, a bacterium found in higher levels in the gut of lean individuals induces the production of a thickened gut mucus layer. The aims of this article are to elucidate the different physiological, biochemical and physical properties of bodily mucus, a keen appreciation of which will help circumvent the slippery slope of challenges faced in achieving effective mucosal drug and gene delivery.

胃肠道，眼睛，鼻子，肺，子宫颈和阴道的粘膜上衬有散布着粘液分泌杯状细胞的上皮，所有这些都有助于它们的独特功能。该粘液为上皮提供了针对有害物质和病原体的不可或缺的防御力。但是，它同样可以成为针对上皮被动和主动转运机制的药物和输送系统的障碍。这篇综述重点介绍了在人体不同粘膜表面表达的各种粘蛋白，以及它们在创建粘液样结构以保护具有特殊功能的上皮细胞中的作用。已经讨论了损害粘液屏障特性的各种因素，并着重于疾病状态和微生物群如何改变粘液的物理特性。例如，Akkermansia muciniphila是一种瘦肉个体的肠道中含量较高的细菌，会诱导肠粘液层增厚。本文的目的是阐明身体粘液的不同生理，生化和物理特性，对此的敏锐理解将有助于避免在实现有效粘膜药物和基因递送方面所面临的挑战。