第一节概述一、消化和吸收的概念人体进行新陈代谢不仅要从外界摄取氧气,还要从外界摄取各种营养物质。食物中的营养物质包括蛋白质、脂肪和糖类,这些营养物质一般都是难于溶解的大块物质,不能为机体所利用。必须先在消化道内经过分解,变成结构简单的小分子物质如氨基酸、甘油、脂肪酸、葡萄糖等,才能透过消化道粘膜的上皮细胞进入血液循环,供机体利用。食物在消化道内的分解过程称为消化;经过消化后的 Section I Overview First, the concept of digestion and absorption The body’s metabolism not only from the outside world to take in oxygen, but also from the outside world intake of various nutrients. Nutrients in food include proteins, fats and sugars, which are generally large, hard-to-dissolve substances that can not be used by the body. Must be digested in the digestive tract, into a simple structure of small molecules such as amino acids, glycerol, fatty acids, glucose, etc., through the epithelial cells of the mucous membrane of the digestive tract into the blood circulation for the body to use. The decomposition of food in the digestive tract is called digestion; after digestion