Kauffman G L
J Clin Gastroenterol. 1981;3(Suppl 2):45-50.
Gastric mucus, a viscous gel that coats the entire gastric mucosa, is produced by and secreted from the surface epithelial cells. Although 95% water by weight, gel mucus is a polymer of four equal-sized subunits joined by disulfide bridges. Carbohydrate side chains include N-acetylglucosamine, N-acetylgalactosamine, galactose, fucose, neuraminic acid, and sialic acid. At a concentration of about 20 mg/ml, the viscosity begins to rise, and a gel is formed. The thickness of the gel mucus layer is dynamic, and a function of release from surface epithelial cells and mechanical and proteolytic degradation within the lumen. An increase in luminal fluid glycoprotein output has been observed in response to splanchnic and vagal nerve stimulation, topical acetylcholine, prostaglandins, carbenoxolone, and parenteral secretin. Topical prostaglandins and carbenoxolone have been observed to increase mucus gel thickness. Gastric bicarbonate secretion is also thought to be a function of the surface epithelial cell. The magnitude of stimulated gastric bicarbonate secretion is 5 to 10% of maximal acid secretion for a given surface area of mucosa. Stimulants of gastric bicarbonate secretion are carbachol, Ca++, c-GMP, 16-16 dimethyl PGE2, and PGF2 alpha. Inhibitors of gastric bicarbonate secretion include atropine, metabolic inhibitors, acetazolamide, alpha-adrenergic agents, and inhibitors of prostaglandin synthesis. Taken together, these observations lend credence to the hypothesis that an unstirred layer of mucus, rich in bicarbonate, may offer significant protection against acid-peptic mucosal injury by neutralizing luminal acid and thereby providing the apical membrane of the surface epithelial cell with a near neutral pH milieu.
胃黏液是一种覆盖整个胃黏膜的黏性凝胶，由表面上皮细胞产生并分泌。尽管按重量计算95%是水，但凝胶状黏液是由四个大小相等的亚基通过二硫键连接而成的聚合物。碳水化合物侧链包括N-乙酰葡糖胺、N-乙酰半乳糖胺、半乳糖、岩藻糖、神经氨酸和唾液酸。当浓度约为20毫克/毫升时，黏度开始上升并形成凝胶。凝胶状黏液层的厚度是动态的，取决于表面上皮细胞的释放以及管腔内的机械和蛋白水解降解作用。已观察到，对内脏和迷走神经刺激、局部应用乙酰胆碱、前列腺素、甘珀酸和肠外给予促胰液素，管腔内液体糖蛋白输出会增加。已观察到局部应用前列腺素和甘珀酸可增加黏液凝胶厚度。胃碳酸氢盐分泌也被认为是表面上皮细胞的一项功能。对于给定表面积的黏膜，刺激后胃碳酸氢盐分泌量为最大胃酸分泌量的5%至10%。胃碳酸氢盐分泌的刺激物有卡巴胆碱、钙离子、环磷酸鸟苷、16,16-二甲基前列腺素E2和前列腺素F2α。胃碳酸氢盐分泌的抑制剂包括阿托品、代谢抑制剂、乙酰唑胺、α-肾上腺素能药物和前列腺素合成抑制剂。综上所述，这些观察结果支持了这样一种假说，即富含碳酸氢盐的未搅动黏液层可能通过中和管腔内的酸，从而为表面上皮细胞的顶端膜提供接近中性的pH环境，对酸-消化性黏膜损伤提供显著保护。
