An Introduction to Hypotonic Solution

Tonicity refers to a solution's relative solute concentration in comparison to another solution. A hypotonic solution is a type of tonicity. It is one in which the concentration of soluble chemicals outside the cell is less than that inside the cell.

In a hypotonic solution, the solute concretion is always smaller than the cell. There is less solvent because there is a high concentration of solute inside the cells (water).

What is Hypotonic Solution?

Hypo denotes low, hence a hypotonic solution is one that has a higher water content than solute concentration. A solution is a molecularly dispersed mixture of one or more compounds in a sufficient quantity of dissolving solvent. A solute is a dissolved material in a solution. What enters and leaves the cell is regulated and controlled by the cell membrane. A selectively permeable membrane is a membrane that enables certain materials to pass through but not others.

In a hypotonic solution, the solute concretion is always smaller than the cell. There is less solvent because there is a high concentration of solute inside the cells (water).

Osmosis is a process in which water passes through a semipermeable membrane from a high concentration to a low concentration. The fact that the solute concentration is low in this solution implies that the solvent concentration is high. Water flows from the outside to the inside of the cell.

Hypertonic and Hypotonic Solution

A hypertonic solution is one in which the concentration of solutes in the solution is higher than the concentration of the cell in the solution. Saltwater is an example of a hypertonic solution. Whereas a hypotonic solution is a solution that has more water outside the cell. Water then travels into the cell from the solution.

Both animal and plant cells have been shown to be affected by hypertonic and hypotonic solutions. Hypertonic solution has a higher solute content and less water than a cell. There is a net migration of water from inside to outside the cell because the concentration of water is higher within the cell. Osmosis allows water to leave the cell. The loss of water causes the cells in a hypertonic solution to shrink. The animal cell will shrivel up in a hypertonic solution. This is known as crenation. The plant cell becomes less stiff in a hypertonic solution, which is known as plasmolysis.

In a hypotonic solution, The water enters the cell due to high solute concentration inside the cell. The water is more in this hypotonic solution and solute concentrations are low.

Hypotonic solution

Image: Hypotonic solution

Hypotonic Solution Example

Hypotonic solutions involve distilled and clean water. Hypotonic solutions include 0.45 per cent saline and 5% dextrose in water (this is technically isotonic, but once the dextrose is absorbed, it operates on the body as if it were hypotonic).

When Cells are Placed in a Hypotonic Solution

A hypotonic solution contains a lower concentration of solutes and a higher concentration of solvent. Water fills a cell through osmosis when it is placed in a hypotonic solution. Due to the lack of a cell wall, animal cells enlarge and explode.

During hypotonic solution, the animal cell ruptures. This is called hemolysis. The plant cell would load up and become much stiffer in a hypotonic solution, and this is known as turgor pressure. The plant cell has a cell wall that exerts reverse pressure on the cell membrane.

Administration of Hypotonic Solution

Hypotonic solutions are frequently employed to dilute extracellular fluid and rehydrate cells in individuals with hypertonic fluid imbalances, as well as to treat gastric fluid loss and dehydration caused by severe diuresis. This type of solution contains no calories or other electrolytes, but it does contain free water, salt, and chloride. The cell has a low amount of extracellular solute and wants to shift into the cell to utilise standard osmosis. This promotes cell swelling, which can result in the cell bursting or lysing.

0.45 percent saline (1/2 NS), 0.225 percent saline (1/4 NS), and 0.33 percent saline (1/3 NS) are hypotonic solutions. When a cell is dehydrated and fluids must be reintroduced, hypotonic solutions are used. This happens when a patient develops diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemia.

When we talk about Intravenous (IV) fluids, we usually mean that the water wants to exit the intravascular region and enter the Red Blood Cells (RBCs). The most common cause of giving 0.45 percent salinity is real dehydration, which occurs when the body loses solely water and no electrolytes (this is different from fluid volume deficit, when the body loses both water and electrolytes). The body already has a normal amount of electrolytes in dehydration. Therefore, there is no need to add extra to the IV solution. Only some of the patient's water needs to be refilled.


A hypotonic solution has the feature that it has a low solute concentration as compared to the cell. This causes cell swelling, and this property is used in some clinical trials to treat patients. This type of solution is provided intravenously and helps to regain the normal state of the cell and body. This article helps to understand the properties of the hypotonic solution and its meaning. It has provided all the information regarding hypotonic solutions with examples.

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FAQs on Hypotonic Solution

1. What are hypotonic considerations?

The hypotonic solution is used in clinical trials to treat dehydration in the body. Although these solutions hydrate cells, they may deplete fluid in the circulatory system. DKA (hyperosmolar hyperglycemia) is treated by shifting fluid from the venous system into the cells and interstitial spaces. These can promote hypovolemia and hypotension. These can lead to vascular collapse, watch for volume deficit, older people may experience disorientation or dizziness. Because of the risk of hypovolemia, never administer to those with high ICP, liver disease, trauma, or burns.

2. What are the objectives of IV Solutions?

Fluid and electrolyte abnormalities are corrected and/or prevented via IV fluid injection. It is critical to understand the correct ordered solution, the reasons for its use, and how to identify and correct infusion-related problems. Hypotonic, isotonic, and hypertonic solutions are among the many options available. The hypotonic solution has a lower solute concentration as compared to the cell. These solutions are used to regain hydration in the body. The cells in the hypotonic solution burst due to water moving inside the cell. 

3. How can you tell whether a solution is hypotonic?

A solute and a solvent are present in the solution. A liquid and water make up a solvent. A solution is created when a solid solute dissolves in a liquid solvent. To determine if a solution is hypotonic or not, we must first determine the solute concentrations by adding a cell with a known concentration of solute. And the solute concentration should be high from the solution. When the cell is swollen in this solution, the presence of water movement indicates that the solution is hypotonic. 

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