Hypertonic Solution: Definition, Function and Examples of This Essential Fluid for Life

Cells require particular conditions to function correctly.

The temperature, the amount of water, and nutrients must all be correct for a cell to be healthy, and these optimal conditions vary according to the organism.

The amount of fluid inside and outside a cell is a critical condition, and this amount of fluid is often determined by the number of solutes outside the cell.

The solutes are dissolved particles in a solvent and together form a solution. In the body, these solutes are ions like sodium and potassium.

Three solutions can occur in the body based on solute concentration: isotonic, hypotonic, and hypertonic.

  • Isotonic: an isotonic solution is one in which the concentration of solutes is the same inside and outside the cell.
  • Hypotonic: a hypotonic solution is when the concentration of solutes is higher inside the cell than outside it.
  • Hypertonic: a hypertonic solution is where the concentration of solutes is greater outside the cell than inside it. A hypertonic solution contains a higher concentration of solutes compared to another solution.

With a lower concentration or osmolarity, the opposite solution is known as the hypotonic solution. In biology, scientists must describe the contents of cells compared to the environment.

The function of the hypertonic solution

If a cell is placed in a hypertonic solution, the cell will be hypotonic. If the cell’s cytosol is a hypertonic solution, it means that the environment is hypotonic or more weakly concentrated.


This is important because solutes and water tend to flow or diffuse along their gradients. Two-hybrid solutions will eventually become a single solution. The solutions will become isotonic if the answers are separated by a permeable membrane that only allows water to pass through.

Isotonic solutions have equal concentrations, although they can have different volumes. The plasma membrane surrounding cells is a special permeable membrane that separates the cell’s contents from the environment.

The plasma membrane is embedded with particular membrane transport proteins that help transport solutes. It also has special protein channels called aquaporins that allow water to flow freely through the membrane.

The cell must use energy to move solutes in and out of the cell actively. Too many solutes and the cytosol will become a hypertonic solution compared to the environment.

Cells without cell walls can burst in this condition. Too few solutes and the environment will become the hypertonic solution. In this case, the opposite will happen as the water moves out of the cell.

Water moves against the solute concentration gradient, moving from low solute concentration to areas of high solute concentration. In another sense, water moves with the water concentration gradient, from high water concentration to areas of low water concentration.

The organisms that regulate the osmolarity of your cells are known as osmoregulation. Generally, cells try to maintain their cytoplasm as a hypertonic solution compared to the environment.

While this poses some structural issues, it allows water to flow freely through the cell and participate in many of the reactions where it is necessary. If cells were hypotonic, they would eventually lose most of their water to the environment.

Other organisms, osmoconformers, have the same osmolarity as the environment, although the same solutes may be different. This ensures that they neither lose nor gain a lot of water.

Examples of the hypertonic solution

Human kidney

To regulate the amount of water in the body, the human brain has particular proteins called osmoreceptors, which can measure the osmolarity of the environment around the cell.

If the environment becomes a highly hypertonic solution, there is not enough water in the blood to dilute the solutes.

The hypothalamus releases hormones and increases the permeability of the membranes in the kidney. The kidney reabsorbs the water that would have been excreted and adds it back to the bloodstream. Blood becomes more isotonic compared to cells, and standard processes can continue.

Plants in a hypertonic solution

In general, plants prefer to live in hypotonic environments. In a hypotonic environment, plant cells are easily flooded by water, and they can remain upright or rigid due to the pressures exerted on their cell walls by the influx of water.

Plants use this water potential to give their bodies structure and move water from the roots to the top of the plant. However, many plants have adapted to live in hypertonic environments.

Coastal marshes, mangroves, and other brackish waters have a much higher salt content than freshwater. The soil becomes saturated with these salts, creating a much higher solute concentration in the ground.

Most plants would wilt if transplanted into this habitat, but a particular group of plants known as Halophytes has evolved to overcome this obstacle.

By increasing the osmolarity of their roots, plants can change from a hypotonic environment within the cell compared to the environment to a hypertonic solution in the cytosol. This reduces the water potential of the root cells and allows water to enter the cells.

Cells store excess salts in the roots or transport the salts to the leaves, where they can be excreted from the glands.

Osmoregulation of sea turtles

Compared to freshwater, saltwater is a hypertonic solution. This means that for cells to function, they must contain a cytosol that is a more hypertonic solution than saltwater. Sea turtles, for example, live in a much more hypertonic solution than freshwater turtles.

If you place a freshwater turtle in seawater, the hypertonic seawater will dehydrate the turtle. Instead of being hydrated by water, the solute-rich ocean water will draw moisture out of the body to balance the difference in osmolarity.

Sea turtles and other marine animals have developed unique ways to remove excess salts to overcome this obstacle. The salts move from the digestive tract into the bloodstream. When they reach the salt gland, they are released.

This creates an internal environment higher in solutes but does not lose excessive amounts of water to the environment.

Hypertonic solutions

  • 3% saline solution.
  • 5% saline solution.
  • 10% dextrose in water (D10W).
  • 5% dextrose in 0.9% saline solution.
  • 5% dextrose in 0.45% saline solution.
  • 5% dextrose in lactated Ringer.