Question

When a patient suffering from dehydration was admitted to a hospital, the doctor started him on an intravenous therapy with an isotonic saline solution. Why was he not treated with a solution of normal water?

Short answer

The patient was treated with an isotonic saline solution instead of normal water to prevent water from rushing into cells via osmosis, which could cause the cells to swell and potentially burst. An isotonic solution has the same concentration of solutes as the patient's blood, which enables hydration without disrupting the body's equilibrium.

Step-by-step solution

Understand the Concept of Osmosis

Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. So, in the context of the body, cells are surrounded by a semi-permeable membrane and have a certain concentration of salts.

Understand the Effect of Pure Water

When pure water is introduced into the bloodstream, it will have a higher water concentration than the cells. As a result, via osmosis, water will rush from the higher concentration (bloodstream) to the lower concentration (cell), causing swollen and potentially bursting cells.

Explain the Use of Isotonic Saline Solution

An isotonic saline solution has the same concentration of salts as the body's cells and blood. Introducing this into the bloodstream will not disrupt the balance of water concentration, avoiding any harms related to osmosis. Cells remain stable as there is no net movement of water.