Question

If the sodium ion concentration outside the cell increases, and the CFTR channel is open, in what direction will chloride ions and water move across the cell membrane?

A) Chloride ions will move out of the cell, and water will move into the cell.
B) Both chloride ions and water will move out of the cell.
C) Chloride ions will move into the cell, and water will move out of the cell.
D) Both chloride ions and water will move into the cell.
E) The movement of chloride ions and water molecules will not be affected by changes in sodium ion concentration outside the cell.

Answer 1

Chloride ions and water both will move out of the cell in response to an increased sodium ion concentration outside the cell, facilitated by open CFTR channels, aligning with principles of electrochemical gradients and osmosis.

Step-by-step explanation:

B) Both chloride ions and water will move out of the cell. This is due to the increase in the concentration gradient of sodium ions outside the cell and the function of CFTR channels.

When the sodium ion (Na+) concentration outside a cell increases, it creates a higher osmotic pressure in the extracellular fluid (ECF). Because body fluids strive to maintain neutrality in charge, an increase in Na+ concentration can drive the movement of chloride ions (Cl−) to balance the charge. If the CFTR channel is open, as indicated in the question, chloride ions will tend to move from areas of lower Na+ concentration (inside the cell) to higher Na+ concentration (outside the cell) following the electrochemical gradient.

As Cl− moves out, it increases the osmolality of the ECF further. Water tends to follow ions to maintain osmotic balance. Therefore, water will move out of the cell into the ECF, where the concentration of ions is higher. This movement follows the basic principles of osmosis, which states that water moves from areas of lower solute concentration to higher solute concentration until equilibrium is reached.