umen Epithelium Interstitial space 糖的吸收 A DIGESTION OF STARCH IN LUMEN B DIGESTION OF OLIGOSACCHARIDES AT BRUSH BORDER Carbohydrates Lumen toplasm a-Amylase Lactase Lactase splits lactose Both monomers are Amylopectin ansported via SGLTI bb△ Lactose The three monosaccharide SGLT1 Terminal Adjacent a-1,6 linkage Adjacent Terminal products of carbohydrate a-14 link a-1,4 link(branching)a-1A link a-1.link Glucoamylase (also known as maltase) digestion- glucose, galactose Cannot be at removes glucose 2 Na. by amylase by amylase monomers for transport and fructose-are absorbed by the small intestine in a two-step process(两步机制) involving bb.b √bb bbb their uptake across the apical Maltotriose a-Limit dextr Maltotriose ol maltose membrane into the epithelial cell wb Sucrase-isomaltase is actually SGLT1 and their coordinated exit across Maltose the basolateral membrane splits sucrose, as well as maltose and maltotriose 2 Nae GLUT5 The Na/glucose transporter 1 C ABSORPTION OF MONOSACCHARIDES (SGLT1)is the membrane protein Sucrase-isomaltase responsible for glucose and SGLT1 o Sucrose galactose uptake at the apical Galactose○ G| ucose○ ③ O Maltose membrane. the exit of all three b Glucoseo 2 Na( GLUT2 O monosaccharides across the ◆2K basolateral membrane uses a GLUT2 O SGLT facilitated sugar transporter GLUT5 b Fructose (GLUT2) O Maltose Maltotriose The isomaltase moiety splits a-limit dextrins, as wellas糖的吸收 Carbohydrates The three monosaccharide products of carbohydrate digestion— glucose, galactose, and fructose—are absorbed by the small intestine in a two-step process（两步机制）involving their uptake across the apical membrane into the epithelial cell and their coordinated exit across the basolateralmembrane. The Na/glucose transporter 1 (SGLT1) is the membrane protein responsible for glucose and galactoseuptake at the apical membrane. The exit of all three monosaccharides across the basolateralmembrane uses a facilitated sugar transporter (GLUT2)