In our day-to-day life we come across many situations like, “this organism is particularly suited to only this environment and our body needs this much of water and salts to stay hydrated”, and all other things.
The reason behind this is hypotonicity.
Generally, a solution is referred to as hypotonic if it has lower concentration of solute on comparing it with other solution.
Here in Hypotonic, Hypo refers to under/ low/ beneath and tonic refers to concentrate of solutions.
The phenomenon of hypotonic solutions leads to Hypotonicity.
What is Hypotonic Solution?
A solution is said to be hypotonic if it contains a small amount of solution comparable to the cytosol of the cell.
Tonicity is the measure of effective osmotic pressure and water permeability through a semi permeable membrane, which is used to measure the response of the cell when immersed in external solutions.
Examples of Hypotonic Solution
In biology, hypotonic solutions can be explained in relation to blood serum.
On considering blood serum, solutions having osmolarity less than 280 m Osm/litre are referred to as hypotonic solutions.
Hypotonic saline, 2.5% dextrose solution, etc are some of the examples of the hypotonic solutions that are hypotonic comparing with blood serum and are regulated as hypotonic intravenous solutions.
Is Water a Hypotonic Solution?
Water is one of the typical examples of hypotonic solution.
Water is generally a solvent and purified or distilled water will be a promising hypotonic on comparing it with other solutes.
Purified distilled water is a comparatively pure and hence it is considered to be hypotonic to any of the aqueous solute.
Effects of Hypotonic Solutions
A. Animal Cells: If the concentration of water is higher outside on comparing inside of the cell, as a result in movement of water from outside into the cell and as a results cell gains water and swells.
On swelling the internal pressure of the cell increases and it leads to rupturing of a cell or hemolysis.
B. Plant Cells: In case of plant cells the cell swells by increasing its volume and pushes the cell against the cell wall and causes turgidity but not lysis because the cell wall protects it from becoming lysed and these cells also do not stay turbid for a longer period.
Animal cell don’t have the capacity to stay turbid as it lacks cell wall.
C. Protists: Tonicity is essential for regulating the life of almost every organisms. Considering the protists such as paramecia and amoebae which are able to retain their structure due to tonicity regulation though they do not have a cell wall or a cytoskeleton.
As these organisms live in a hypotonic environment where continuous water influx occurs which helps the cell to maintain a definite structure and prevent it from cell lysis.
These organisms contain contractile vacuoles which in the sense acts as a specialized organ to retain excess of water from the cell.
D. Mangroves and Marshy Areas: Considering the areas of mangroves and marshy, they have a high hypertonic environment due to high salt content.
A normal plant will not survive in such extreme conditions. However, those plants which exist in marshy areas or mangroves adapted themselves to create a hypertonic condition in their root cells.
As a result, hypotonic condition around the roots in their external environment helps these plants to absorb water from the surroundings.
E. Freshwater Fishes: Aquatic animals living in freshwater or near seawater adapt a condition to regulate osmoregulation.
Due to this condition, salt content in the water is critical for the aquatic life in any water body.
Sea turtles have adapted themselves to a hypertonic environment with the help of their salt glands.
Thus, these adaptations help the aquatic or freshwater or marine animals to survive in critical hypotonic conditions.
F. Humans: When human body loses excess sodium comparing to that of water loss it results in reduced serum osmolarity. Which is relatively known as hypotonic dehydration.
This condition results in influx of water from extracellular to intracellular space which leads to swelling of the cells.
Thus, the imbalance of sodium in the cells leads to many neurological effects such as nausea or vomiting, confusion, edema etc.
Sometimes in most extreme cases it may also lead to unconsciousness, coma or death.
Considering all these cases it is important to understand that hypotonic dehydration which leads to cell swelling and edema are all due to excessive water retention.
This condition occurs if there is an excessive loss of fluid due vomiting, diarrhea or through burns and wounds.
Sometimes it is also due to Addison’s disease, renal tubular acidosis or because of chronic use of diuretics or over use of intravenous hypotonic fluids or regular saline in patients or hypotonia.
The normal range of blood sodium level in our body ranges from 135-145mEq/ L.
Hypotonia is a condition where sodium in our body falls below 135mEq/L.
This condition results in various heart disease, kidney failure etc. Drinking too much of water and decreased intake of salts may lead to this condition.
Why Freshwater Fishes Can't Survive in Seawater?
We know that freshwater fishes cannot survive in sea water.
The fact that these fishes survive in freshwater as they have higher amount of salt concentrations in their body on comparing with lakes and rivers on which they survive.
So, if these fishes are exposed to sea water, due to hypotonic conditions water will be removed from the body of those fishes and which leads them to dehydrate and perish.
Thus, change in salt content of the water body drastically affects the fish population in any water body.
How Cells Regulate in Hypotonic Solution?
Mushrooms which are one species among the fungus, maintain a hypotonic environment around their cell to maintain the influx of water which helps in regulation of turgor pressure.
This helps the cells to remain rigid which also helps in maintaining their erect structure.
These species also utilise this pressure from the cells to transport water throughout their surface.
This is the reason why plants look wilted in appearance if they are not watered for a long time.
Thus, loss of the turgidity in plants results in wilting of the plant or a specified organism.
Again, on rewatering turgor pressure is generated in plants which helps them to retain their structure and their lost shape.
Symptoms of Hypotonicity
Hypotonicity may lead to nausea, vomiting, oedema, headache, Loss of energy which leads to drowsiness and fatigue and sometimes it may also lead to seizures or coma.
Hypotonic Solutions as a Treatment
When our cells are dehydrated, the fluids need to be put back to be intracellular. This condition often happens when a patient develops diabetic ketoacidosis (DKA) or hyper osmolar hyperglycemia.
In such cases the administration of hypotonic solutions rehydrates the cells.
Thus, hypotonic solutions play an important role in maintain all organisms and helps them to adapt a particular environment.
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- Hypotonic versus isotonic maintenance intravenous fluid therapy in hospitalized children: a systematic review. Clin Pediatr (Phila) . 2007 Nov;46(9):764-70.
- Isotonic versus hypotonic saline solution for maintenance intravenous fluid therapy in children: a systematic review. Pediatr Nephrol . 2015 Jul;30(7):1163-72.