How is an isotonic solution defined in terms of osmolarity?

An isotonic solution is defined as one that has the same osmolarity as bodily fluids, such as blood plasma or extracellular fluid. This means that the concentration of solutes in the isotonic solution is equal to that in the bodily fluids. When two solutions have equal osmolarity, there is no net movement of water across a semipermeable membrane, maintaining cell integrity and function.

In this context, maintaining osmotic balance is crucial for homeostasis. If a solution were to have a higher or lower osmolarity compared to bodily fluids, it could result in the movement of water either into or out of cells, potentially causing cellular swelling or shrinkage, which can be detrimental to their function. Therefore, understanding isotonic solutions is vital for medical applications, particularly in intravenous therapy and fluid management.