Question

Blood is isotonic with (a) \(0.9 \%(\mathrm{w} / \mathrm{v})-\mathrm{NaCl}\) solution (b) \(0.9 \mathrm{M}-\mathrm{NaCl}\) solution (c) \(0.9 \mathrm{M}-\mathrm{NaCl}\) solution (d) \(9.0 \%(\mathrm{w} / \mathrm{v})-\mathrm{NaCl}\) solution

Short answer

Blood is isotonic with option (a) 0.9% (w/v) NaCl solution.

Step-by-step solution

Understanding Isotonic Solutions

A solution is considered isotonic with blood when it has the same osmotic pressure as blood plasma. This means that the concentration of solutes in the solution is similar to that of blood plasma to prevent osmosis, or the movement of water into or out of cells. A commonly known isotonic solution with blood is 0.9% (w/v) NaCl, which has the same solute concentration as blood plasma.

Analyzing the Options

Option (a) is a 0.9% (w/v) NaCl solution, which means that there are 0.9 grams of NaCl in 100 mL of solution. This is the typical concentration of a saline solution that is isotonic with blood. Option (b) and (c) are both 0.9 M (molar) solutions, which would be much higher in concentration compared to a 0.9% w/v solution, and thus are hypertonic. Finally, option (d) is a 9.0% (w/v) NaCl solution, which is ten times more concentrated than the isotonic solution and hence hypertonic as well.

Identifying the Isotonic Solution

Based on the known isotonic concentration for blood (0.9% w/v NaCl), only option (a) matches this criterion. Therefore, blood is isotonic with a 0.9% (w/v) NaCl solution.

Key concepts

Osmotic Pressure

Osmotic pressure is a fundamental concept in the study of biological systems and the chemistry of solutions. It refers to the pressure that is required to stop the osmotic flow of water across a semi-permeable membrane. Osmosis is the movement of water from an area of lower solute concentration to an area of higher solute concentration, and osmotic pressure effectively measures the tendency of water to move into a solution.

A solution that is isotonic with human blood has an osmotic pressure that matches that of the blood plasma, meaning there is no net flow of water into or out of the body's cells. This is essential in medical applications because incorrect osmotic pressures can cause cells to shrink or swell, leading to serious health issues.

Saline Solution

A saline solution is a mixture of salt, usually sodium chloride (NaCl), in water and has many medical uses, notably in IV fluids to hydrate patients. The concentration of NaCl in a standard isotonic saline solution is 0.9% (w/v), which stands for weight/volume. This means there are 0.9 grams of NaCl in every 100 milliliters of water.

A saline solution with this concentration is isotonic to human blood plasma, making it safe for infusion as it does not alter the cells' environment. Preparing such a solution requires precise measurement to ensure that the concentration matches the osmotic pressure of blood plasma for it to be effective and safe for use in medical treatments.

Hypertonic

When comparing solutions, the term 'hypertonic' is used to describe a solution that has a higher solute concentration than another solution, typically referring to biological fluids. If a solution is hypertonic relative to blood plasma, it has a higher osmotic pressure. As a result, when cells are exposed to a hypertonic solution, water will move out of the cells to balance the concentration difference, causing the cells to shrink.

Examples given in the exercise options (b), (c), and (d) illustrate hypertonic solutions to blood plasma. A 0.9M or 9.0% (w/v) NaCl solution is significantly more concentrated than the isotonic 0.9% (w/v) NaCl solution and thus would draw water out of the cells, leading to cellular dehydration.

NaCl Concentration

The concentration of sodium chloride (NaCl) in a solution has direct implications on its isotonicity, osmotic pressure, and its effect on cells. NaCl is the primary salt used in saline solutions because its ionic components, sodium and chloride, are also primary electrolytes in human blood plasma. A correct NaCl concentration is crucial for maintaining the balance of fluid inside and outside of the body's cells.

The 0.9% (w/v) NaCl concentration noted in option (a) reflects the proper ratio needed to maintain an isotonic condition, where the solution's osmotic pressure mimics that of blood. This crucial balance allows for safe intravenous administration as it ensures normal cell function without disrupting the osmotic equilibrium.

Blood Plasma

Blood plasma is the liquid component of blood in which blood cells are suspended. It contains water, electrolytes, nutrients, waste products, and various proteins. The osmotic balance of blood plasma is tightly regulated because it influences the entire circulatory system, including the health and functioning of red blood cells and other cellular components. Osmotic pressure must be maintained to ensure that cells neither gain nor lose excess water.

Isotonic saline solutions, which have the same NaCl concentration as blood plasma (0.9% w/v), are often used in medical settings to replenish fluids without altering the osmotic balance. This is because the introduction of an isotonic solution into the bloodstream does not change the osmotic gradient across cell membranes, allowing for the safe transfer of water and electrolytes.