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

Cells require very specific conditions in order to function properly.

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 both inside and outside a cell is a condition that is very important, and this amount of fluid is often determined by the amount 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.

There are three types of solutions that 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 both inside and outside the cell.
  • Hypotonic: a hypotonic solution is one in which the concentration of solutes is higher inside the cell than outside it.
  • Hypertonic: a hypertonic solution is one 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.

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

Function of the hypertonic solution

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

This is of great importance because solutes and water tend to flow or diffuse along their gradients. Two mixed solutions will eventually become a single solution. If the solutions are separated by a permeable membrane that only allows water to pass through, the solutions will become isotonic.

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

The plasma membrane is embedded with special 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 actively move solutes in and out of the cell. 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 areas of low solute concentration to areas of high solute concentration. In another sense, water moves with the water concentration gradient, from areas of high water concentration to areas of low water concentration.

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

While this poses certain structural problems, 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 exact 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 special proteins called osmoreceptors, which can measure the osmolarity of the environment around the cell.

If the environment becomes a highly hypertonic solution, it is because 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 normal processes can continue.

Plants in 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.

Seaside marshes, mangroves, and other brackish waters have a much higher salt content than fresh water. The soil becomes saturated with these salts, creating a much higher concentration of solute in the soil.

Most plants would wilt if transplanted into this habitat, but a special 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 fresh water, salt water is a hypertonic solution. This means that for cells to function, they must contain a cytosol that is a more hypertonic solution than salt water. Sea turtles, for example, live in a much more hypertonic solution compared to 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 water out of the body to balance the difference in osmolarity.

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

This creates an internal environment that is 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.