Question

Figure 3.22 A doctor injects a patient with what he thinks is isotonic saline solution. The patient dies, and autopsy reveals that many red blood cells have been destroyed. Do you think the solution the doctor injected was really isotonic?

Short answer

No, the solution the doctor injected was likely not isotonic. The destruction of many red blood cells suggests that the solution might have been hypotonic, causing water to move into the cells, resulting in them swelling and bursting.

Step-by-step solution

Understand Normal Cellular Behavior in Isotonic Solutions

In an isotonic solution, the amount of solute (in this case, saline) is equal both inside and outside the cells. As a result, there is no net movement of water into or out of the cells, so they maintain their usual shape and functioning.

Evaluate Red Blood Cell Damage

It is mentioned that many of the patient's red blood cells were destroyed. This points to the conclusion that the solution injected was not isotonic. The change in cell composition implies a net movement of water either into or out of the cells.

Analyze the Likely Solution Concentration

Given the destruction of the red blood cells, it can be inferred that the solution was likely hypotonic, which means it had a lower solute concentration compared to the inside of the blood cells. In this situation, water would have flowed into cells to maintain equilibrium, causing them to swell and eventually rupture, leading to their destruction.

Key concepts

Cellular Osmoregulation

Understanding cellular osmoregulation is essential to comprehend how cells maintain their internal environment. This process involves the regulation of water and solute concentrations to preserve a cell's fluid balance.

In isotonic solutions, cells are in perfect harmony with their surroundings, as the solute concentration outside the cell is equal to that inside. Thus, cells in an isotonic environment neither gain nor lose water and remain stable, supporting their various functions.

However, cells can encounter environments that challenge their regulation abilities. In the given exercise, the red blood cells did not maintain their usual shape, implying that osmoregulation was compromised due to an imbalance. Such an imbalance can have severe effects, as we see in the patient's unfortunate outcome.

Hypotonic Solution Effects

In hypotonic solution effects, the concentration of solutes is lower outside the cell compared to the inside. This causes water to rush into the cell, following osmosis principles, to equalize solute concentrations on both sides of the cell membrane.

The influx of water increases the internal pressure, leading to cell swelling. While some cells can manage minor swelling, others, such as red blood cells, are more susceptible to bursting, a process known as hemolysis.

This was likely what occurred in the exercise's scenario, where the injected solution must have been hypotonic, resulting in the catastrophic destruction of the patient’s red blood cells. Understanding these effects is crucial for medical practices and the formulation of intravenous solutions.

Red Blood Cell Tonicity

The concept of red blood cell tonicity relates to osmoregulation but specifically focuses on the cell’s ability to maintain its shape and volume in response to the tonicity of its environment.

Red blood cells have a characteristic biconcave shape that helps them function efficiently in oxygen transport. In isotonic solutions, they retain this shape. However, in hypotonic solutions, the tonicity is offset—too much water enters, making them swell and potentially rupture. Conversely, in hypertonic solutions, water exits the cell, causing them to shrivel.

In the medical context, maintaining correct red blood cell tonicity is vital. The autopsy results in the exercise hinted at a hypotonic solution that disrupted this balance, emphasizing the importance of administering the correct solution type to patients.