Final answer:
The sodium cotransport transports sodium ions and glucose molecules from the GI lumen into the cell via symport proteins in a process known as secondary active transport.
Step-by-step explanation:
The sodium cotransport or coupled transport acts to transport sodium ions and glucose molecules from the GI lumen into the cell. This process is known as Symport, which is a form of secondary active transport. Sodium and glucose both bind to symport proteins on the apical surface of the cell and are transported in the same direction. Sodium moves down its electrochemical and concentration gradient into the cell, thereby providing the energy needed to transport glucose against its concentration gradient.
The sodium-glucose symporter is a prime example of this process, enabling the influx of both sodium ions and glucose molecules into the cell. Subsequently, sodium is then actively pumped out of the cell, while glucose exits the cell by facilitated diffusion to enter the interstitial space. This transport mechanism is an example of coupled or symport transport, where two substances are moved in the same direction. Sodium ions move down their electrochemical gradient, while glucose is transported against its concentration gradient.