co-transport

• co-transporters are a type of carrier protein
• they bind two molecules at a time
• the concentration gradient of one of the molecules is used to move the other molecule against its concentration gradient
• glucose is absorbed into the bloodstream in the small intestine
• in the ileum, the concentration of glucose is too low for glucose to diffuse into the blood. so it's absorbed from the lumen of the ileum by co-transport
• 1. sodium ions are actively transported out of the ileum epithelial cells into the blood by the sodium potassium pump, creating a concentration gradient between the lumen of the ileum and the epithelial cells
• 2. this causes sodium ions to diffuse out of the lumen of the ileum into the epithelial cell, down the concentration gradient. done by the sodium glucose co-transporter proteins
• 3. the co-transporter carries glucose into the cell along with sodium, increasing the concentration of glucose inside the cell
• 4. glucose diffuses out of the cell, into the blood, by facilitated diffusion