What is an Isotonic solution?

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A solution is a mixture of two or more  substances. It has a solvent and a solute. Depending on the concentrations there are different kinds of solutions and their applications differ too. Isotonic solutions have the same salt concentration as the surrounding blood cells. So an isotonic solution will have no effect on the surrounding cells. The cells will not gain or lose water if place in isotonic solution.  The normal Saline solution which is 0.9% NaCl is isotonic with blood and is used in patients suffering from dehydration or if they can't take any liquids or food.


What is a Solution?

A mixture of two or more substances blended homogenously is called a solution. The substance in which other substances are dissolved is called as solvent and the substances which are dissolved are called as solutes. A solution can be present in any of three states: solid, liquid and gas form which is decided by the substances mixing in the solution along with the temperature and pressure conditions.


What are the Different types of Solutions?

In general solutions are categorized into:

  • Hypertonic solution: This is the solution having higher concentration of solute
  • Hypotonic solution: It’s that solution which has lower concentration of solute
  • Isotonic solution: These are two solutions having similar solute concentration



What is Osmosis?

So as to understand the working of isotonic solutions in detail it is necessary to first understand the process of osmosis. Many times two solutions with different concentrations are separated by various membranes like cell membrane which are semi permeable, water molecules start moving from the higher concentration region to the lower concentration region and this process is continuous till the two solutions reach equilibrium of concentration. This process is called as osmosis. One of the most visible examples of semi permeable membrane is skin because the skin allows permeability of water but is very impermeable to almost all solutes.



What are Isotonic Solutions?

A solution which has the same concentration as present in the blood or cells of body is an Isotonic solution. Such cells neither absorb water nor lose any water molecule. Saline solution is a common example of isotonic solution. The tonicity or concentration is important in the medical field as it directly affects the living cells. When cells are placed in higher concentration solution, the cell is bound to swell and at one time ruptures letting the water molecule move to a solution with lower concentration. Similarly, when a living cell is placed in a solution with less concentration(hypertonic solution), it shrinks  as the water molecule move out. This is the reason vaccines are administered in isotonic solutions to balance the fluid level. A person swimming in the sea for a long time can experience the effects of being in a hypertonic solutionand tend to loose lot of water which may even can result in death. 



How are sports drink associated with these solutions?

Sports drinks are made keeping in view the properties of hypertonic, hypotonic and isotonic solutions in mind. The sports drink which are hypertonic solutions comprise of excess solutes like sugar and salts than the body. These drinks are very useful for the body as they replenish our body with more glucose. On the other hand, the hypotonic solutions or sports drinks have solutes in lower concentration as compared to the cells in the body, due to which when you drink such sports drinks the cell walls of the body will gain more fluid. Sports drinks are used by athletes to help them keep hydrated without adding extra glucose to their drinks. Isotonic supplements in the form of tablets and vitamin pills are available in the market which help the body in absorbing vitamins better than the traditional tablets.



Why should Animal cells be Isotonic?

Animal cells do not have a cellwall like plants cells but do have a plasma membrane which helps in maintaining an equilibrium in ionic concentrations of the plasma.The cell has to maintain an isotonic concentration as this is the only way to keep its cell shape and helps the cell from shrinking(also known as crenation) which will occur if the solution is hypertonic or the cell can burst if the cell contents are hypotonic. The plasm membrane is permeable and performs an important task of keeping the cell alive by maintaining an isotonic environment.



How do Marine animals survive in Salt Water?

The sea water is hypertonic to the extracellular fluid of many of the marine vertebrates. These marine animals overcome the problem of hypertonicity by pumping out the salt water which they accomplish by taking sea water continuously and expelling the ions from their gills thus removind the salt. Sea birds which spend long time away from fresh water also have adapted a similar mechanism.They take in salt water and process it to remove the salt. Some of the birds have salt glands which extract the salt from the body and expel it through their nostrils.


For more information on related topics. click on the links below:

Uses of hypertonic solutions 

What is Osmoregulation

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