The mechanism of the sodium-potassium pump

• Firstly, sodium ions are actively transported out of epithelial cells via the sodium-potassium pump using a specific carrier protein in the epithelial cell-surface membrane.
• Since sodium ions leave the epithelial cells, there is a much higher concentration of sodium ions inside the lumen of the intestine than inside the epithelial cells.
• Due to the sodium ion concentration gradient established between the lumen of the intestine and the epithelial cells, sodium ions diffuse into the epithelial cells through a co-transport protein within the cell-surface membrane. As they diffuse, they bring glucose or amino acid molecules with them.
• Once glucose or amino acids have moved into the epithelial cells via co-transport, they will move into the blood plasma via facilitated diffusion.
• Co-transport of glucose and amino acids is an indirect form of active transport - the sodium ion concentration gradient powers the movement of glucose and amino acids into cells, instead of ATP energy directly.