Osmosis and tonicity
How it works
- If the extracellular fluid has lower osmolarity than the fluid inside the cell, it’s said to be hypotonic—hypo means less than—to the cell, and the net flow of water will be into the cell.
- In the reverse case, if the extracellular fluid has a higher osmolarity than the cell’s cytoplasm, it’s said to be hypertonic—hyper means greater than—to the cell, and water will move out of the cell to the region of higher solute concentration.
- In an isotonic solution—iso means the same—the extracellular fluid has the same osmolarity as the cell, and there will be no net movement of water into or out of the cell.