How does tonicity affect cells in the human body?

Tonicity refers to the relative concentration of solutes in a solution compared to another solution, particularly with respect to cells. It plays a crucial role in the movement of fluids in and out of cells through osmosis, which is the process where water moves across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration.

When cells are placed in solutions of different tonicities—such as hypertonic, hypotonic, or isotonic—their volume and shape can change significantly. In a hypertonic solution, water moves out of the cells, causing them to shrink (crenation). In a hypotonic solution, water enters the cells, leading to swelling or possibly bursting (lysis). On the other hand, in an isotonic solution, there is no net movement of water, and the cells maintain their normal shape and size.

Understanding how tonicity affects the movement of fluids in and out of cells is essential for IV technicians, as it directly influences the selection of intravenous fluids and the management of patient hydration and electrolyte balance.