维生素 A 是构成视网膜感光色素的主要成份。如果机体缺乏维生素 A,会出现眼睛角膜和结膜干燥、发炎。此外,维生素 A 还有两个重要作用:1.稳定组织上皮细胞的细胞膜,维持皮肤的粘膜的结构完整。呼吸道的气管、支气管内膜也是一种上皮组织,可以防御细菌、病毒的侵袭,是人体防止呼吸道感染的一道坚强屏障。机体若缺乏维生素 A,这道屏 Vitamin A is the main component of retinal pigment. If the body lacks vitamin A, there will be dry and inflamed eyes, cornea and conjunctiva. In addition, vitamin A has two important roles: 1. Stabilize the cell membrane of epithelial cells and maintain the structural integrity of the skin’s mucous membranes. Respiratory trachea, bronchial lining is also an epithelial tissue that can prevent bacteria, viruses, invasion, is the body to prevent a strong barrier to respiratory infections. If the body lacks vitamin A, this screen