Q.Explain what it means for two solutions to be isotonic, and explain, using osmosis, why an intravenous fluid given to a patient must be isotonic with blood plasma rather than distinctly hypotonic or hypertonic.

[!TLDR] Isotonic solutions have equal osmotic pressure, so no net osmotic water flow occurs across a cell membrane; an IV fluid not isotonic with blood would shrink or burst blood cells by osmosis. [!ANSWER] IV fluids must be isotonic with blood plasma …

Two solutions are isotonic when they have equal osmotic pressure at the same temperature, which means no net osmotic flow of solvent occurs between them if they are brought into contact across a semipermeable membrane (such as a red blood cell's membrane). If an intravenous fluid were markedly hypotonic (lower osmotic pressure) relative to blood plasma, water would flow by osmosis from the fluid into the blood cells, causing them to swell and potentially burst (haemolysis). If the fluid were markedly hypertonic (higher osmotic pressure), water would instead flow out of the blood cells into the surrounding fluid, causing them to shrink and shrivel (crenation). Both outcomes damage the cells and can be medically dangerous, which is exactly why intravenous fluids (such as normal saline) are care …

Define isotonic solutions via equal osmotic pressure, then reason through what osmosis would do to a blood cell if the …

Do not describe the danger only in one direction (e.g. only mentioning bursting) — both a hypotonic fluid (cell swelling/bursting) and a hypertonic fluid (cel …