On the membrane of the epithelial cell adjacent to the blood the sodium-potassium pump removes sodium from the epithelial cell lowering its concentration inside the epithelial cell.On the membrane adjacent to the lumen the co-transport protein allows the passage of sodium into the cell by co-transport.Sodium enters the cell down its concentration gradient but draws in amino-acids or glucose through the transport protein along with the sodium ions.This increases the concentration of glucose and amino acids inside the epithelial cell. Glucose and amino acids then diffuse through a carrier protein from the epithelial cell into the blood down their concentration gradient by facilitated diffusion.