In this review we discuss mucus, the viscoelastic secretion from goblet or mucous producing cells that lines the epithelial surfaces of all organs exposed to the external world. Mucus is a complex aqueous fluid that owes its viscoelastic, lubricating and hydration properties to the glycoprotein mucin combined with electrolytes, lipids and other smaller proteins. Electron microscopy of mucosal surfaces reveals a highly convoluted surface with a network of fibers and pores of varying sizes. The major structural and functional component, mucin is a complex glycoprotein coded by about 20 mucin genes which produce a protein backbone having multiple tandem repeats of Serine, Threonine (ST repeats) where oligosaccharides are covalently O-linked. The N- and C-terminals of this apoprotein contain other domains with little or no glycosylation but rich in cysteines leading to dimerization and further multimerization via SS bonds. The synthesis of this complex protein starts in the endoplasmic reticulum with the formation of the apoprotein and is further modified via glycosylation in the cis and medial Golgi and packaged into mucin granules via Ca^2 + bridging of the negative charges on the oligosaccharide brush in the trans Golgi. The mucin granules fuse with the plasma membrane of the secretory cells and following activation by signaling molecules release Ca^2 + and undergo a dramatic change in volume due to hydration of the highly negatively charged polymer brush leading to exocytosis from the cells and forming the mucus layer. The rheological properties of mucus and its active component mucin and its mucoadhesivity are briefly discussed in light of their importance to mucosal drug delivery.

在这篇综述中，我们讨论了粘液，粘液是杯状或粘液产生细胞的粘弹性分泌物，位于暴露于外界的所有器官的上皮表面。粘液是一种复杂的水性流体，由于其粘弹性，润滑性和水化特性，归功于糖蛋白粘蛋白与电解质，脂质和其他较小蛋白质的结合。粘膜表面的电子显微镜检查显示高度曲折的表面具有各种尺寸的纤维和孔网络。粘蛋白是主要的结构和功能成分，是由约20个粘蛋白基因编码的复合糖蛋白，产生的蛋白主链具有多个丝氨酸，苏氨酸的串联重复序列（ST重复序列），其中寡糖是共价O-连接的。通过S S键。该复合蛋白的合成从内质网开始，形成脱辅基蛋白，然后通过顺式和内侧高尔基体中的糖基化进一步修饰，并通过Ca ^{2 +}桥接反式寡糖刷上的负电荷将其包装成粘蛋白颗粒高尔基 粘蛋白颗粒与分泌细胞的质膜融合，并通过信号分子激活后释放Ca ²⁺并且由于高度带负电荷的聚合物刷的水合作用导致体积发生巨大变化，从而导致细胞胞吐并形成粘液层。鉴于粘液及其对粘膜药物传递的重要性，简要讨论了粘液及其活性成分粘蛋白的流变特性。