Answer to Question #126897 in Physics for Vida Nkrumah

Question

When a person receives intravenous fluids to help build up blood volume, why is it important for the fluid to be isotonic

Answer 1

If the fluid is not isotonic, it will lead to the blood cells destruction (lysis). This happens because of osmosis – the spontaneous net movement of water molecules through a cell membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.

The most important inorganic solute of the human cell is sodium chloride. Thus, if the not isotonic fluid (for example distilled water) is entered in the blood stream, the water tends to move inside the cells to equalize the sodium chloride concentration inside and outside the cells. But cells had been already in their stable positions. Thus, extra water will destroy the cells membrane.

That’s why we use the isotonic fluid which contains sodium chloride in the same concentration as in the blood cells.