isosmotik

Isosmotic, also written isosmotik, describes a condition in which two solutions have equal osmolarity, the total concentration of osmotically active particles. This concept is commonly used in physiology, medicine and chemistry to compare a test solution with body fluids or another reference solution. Osmolarity is typically expressed in milliosmoles per liter (mOsm/L) or milliosmoles per kilogram (mOsm/kg).

It is important to distinguish osmolarity from tonicity. Tonicity refers to the effective osmotic pressure that drives water movement across a semi-permeable membrane. A solution can be isosmotic to plasma yet not be isotonic if it contains permeant solutes that cross cell membranes, altering the actual water balance. Conversely, a truly isotonic solution exerts no net water movement across cells because its effective osmolality matches that of the intracellular environment under the given membrane conditions.

Common examples include normal saline (0.9% NaCl), which has an osmolarity around 308 mOsm/L and is isosmotic to human plasma, making it broadly isotonic in clinical use. Ringer’s lactate is another isosmotic IV fluid. Dextrose 5% in water (D5W) is often described as isosmotic at administration, but once glucose is metabolized by cells, the solution becomes hypotonic.

In clinical and research settings, isosmotic comparisons help guide fluid therapy, osmoregulation studies, and the design of experiments that involve cell volume regulation and solute transport. See also isotonic, osmolarity and osmolality.