Chapter 25 - Section 25.6 - Study Guide - Assess Your Learning Outcomes - Page 992: 2

Monosaccharide absorption in the intestinal mucosa primarily occurs through active transport, facilitated diffusion, and secondary active transport. Here's a breakdown of the mechanisms involved: 1. **Active Transport (Sodium-Glucose Cotransporters - SGLTs):** - Active transport is the primary mechanism for the absorption of glucose and galactose. - The apical (luminal) membrane of the enterocytes (cells lining the small intestine) contains sodium-glucose cotransporters (SGLTs), specifically SGLT1. - SGLT1 uses the energy of the sodium ion (Na+) gradient created by the sodium-potassium pump (Na+/K+ ATPase) on the basolateral (serosal) membrane of the enterocytes. - Sodium ions move into the cell along with glucose or galactose molecules against their concentration gradient. - This mechanism ensures that glucose and galactose are efficiently absorbed even when their luminal concentrations are lower than those inside the enterocytes. 2. **Facilitated Diffusion (GLUT Transporters):** - Facilitated diffusion is the primary mechanism for the absorption of fructose. - Fructose is transported into the enterocytes by a facilitated diffusion process involving facilitative glucose transporters, primarily GLUT5. - GLUT5 transports fructose along its concentration gradient, from the lumen into the enterocyte. - Once inside the enterocyte, fructose is converted into fructose-1-phosphate, which is then metabolized further. 3. **Secondary Active Transport (Glucose-Na+ Symport - SGLT1):** - In addition to glucose and galactose absorption via SGLT1, there is a secondary active transport component. - Glucose and galactose that have been transported into the enterocytes via SGLT1 are subsequently transported across the basolateral membrane into the bloodstream. - This process involves a sodium-independent glucose transporter, primarily GLUT2. - GLUT2 allows glucose and galactose to passively diffuse from the enterocytes into the bloodstream, facilitated by the concentration gradient established by SGLT1. It's important to note that these transport mechanisms are essential for maintaining the absorption of monosaccharides in the small intestine. The coordinated activity of these transporters ensures efficient uptake of glucose, galactose, and fructose, which are then transported to the liver via the hepatic portal vein for further processing and distribution throughout the body.

Monosaccharide absorption in the intestinal mucosa primarily occurs through active transport, facilitated diffusion, and secondary active transport. Here's a breakdown of the mechanisms involved: 1. **Active Transport (Sodium-Glucose Cotransporters - SGLTs):** - Active transport is the primary mechanism for the absorption of glucose and galactose. - The apical (luminal) membrane of the enterocytes (cells lining the small intestine) contains sodium-glucose cotransporters (SGLTs), specifically SGLT1. - SGLT1 uses the energy of the sodium ion (Na+) gradient created by the sodium-potassium pump (Na+/K+ ATPase) on the basolateral (serosal) membrane of the enterocytes. - Sodium ions move into the cell along with glucose or galactose molecules against their concentration gradient. - This mechanism ensures that glucose and galactose are efficiently absorbed even when their luminal concentrations are lower than those inside the enterocytes. 2. **Facilitated Diffusion (GLUT Transporters):** - Facilitated diffusion is the primary mechanism for the absorption of fructose. - Fructose is transported into the enterocytes by a facilitated diffusion process involving facilitative glucose transporters, primarily GLUT5. - GLUT5 transports fructose along its concentration gradient, from the lumen into the enterocyte. - Once inside the enterocyte, fructose is converted into fructose-1-phosphate, which is then metabolized further. 3. **Secondary Active Transport (Glucose-Na+ Symport - SGLT1):** - In addition to glucose and galactose absorption via SGLT1, there is a secondary active transport component. - Glucose and galactose that have been transported into the enterocytes via SGLT1 are subsequently transported across the basolateral membrane into the bloodstream. - This process involves a sodium-independent glucose transporter, primarily GLUT2. - GLUT2 allows glucose and galactose to passively diffuse from the enterocytes into the bloodstream, facilitated by the concentration gradient established by SGLT1. It's important to note that these transport mechanisms are essential for maintaining the absorption of monosaccharides in the small intestine. The coordinated activity of these transporters ensures efficient uptake of glucose, galactose, and fructose, which are then transported to the liver via the hepatic portal vein for further processing and distribution throughout the body.