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The word “hyperosmotic” comes from two Greek words: “hyper,” which means “excess,” and “osmos,” which means “thrust” or “push.” A solution that exerts more thrust or pushes through a membrane is referred to as hyperosmotic.
To fully comprehend this concept, we must first comprehend that a solution is created by combining two components, namely a solute and a solvent. Sugar is the solute and water is the solvent in an aqueous sugar solution, for example.
(1) of, pertaining to, or characterised by an elevated osmotic pressure (usually higher than the physiological level);
(2) a state in which the total amount of permeable and impermeable solutes in a solution is larger than that of another solution.
What is Hyperosmotic?
In each system, the quantity of solute in a solution eventually dictates the direction of solvent flow. It is a well-known fact that a concentration difference causes the formation of a concentration gradient, which pushes the migration of molecules from a higher concentration to a lower concentration.
Osmosis is a phenomenon that happens when a concentration gradient causes the solvent (water) molecule to flow through a semi-permeable membrane.
As a result, a hyperosmotic solution is one that has a greater concentration of solute than a comparable solution. Seawater, for example, is hyperosmotic when compared to freshwater or tap water. A freshwater cell gets caught to a hyperosmotic environment when it is placed in a beaker with seawater.
The osmolarity of a solution is the number of solute molecules per volume or weight of the solution. The osmotic pressure exerted by a solution is controlled by its osmolarity. This is especially significant in biological systems when two solutions are separated by a membrane that is typically semi-permeable.
As a result, osmolarity can influence the flow of molecules in a biological system across a biological membrane. Maintaining cellular homeostasis requires the flow of molecules across the biological membrane. As a result, osmolarity is important for cellular homeostasis.
The osmolarity of human serum is kept within a narrow range of 285–295 mOsm/kg. Isotonicity refers to the fact that the majority of human body cells share a comparable osmolarity. Hypertonic and hypotonic fluids are defined as having greater or lower osmolarity than human serum, respectively.
The growth of osmotic pressure, which finally culminates in the creation of osmotic stress in a biological system, is caused by a variation in osmolarity. The pressure or push provided to the solvent molecules to prevent them from passing through the membrane is known as osmotic pressure.
It is critical to recognise at this point that tonicity and osmolarity are not the same thing and should not be confused. Isotonic solutions are not always isosmotic, and vice versa. In the same way, a hyperosmotic solution isn’t always a hypertonic solution. To comprehend this, we must first comprehend the idea of tonicity.
Only non-penetrating solutes have tonicity, which is always dependent on the comparative solution. An isotonic sucrose solution for a mammalian cell will be isotonic, whereas a hypotonic sucrose solution for a plant cell will be hypotonic.
This is because sucrose cannot permeate through a mammalian cell because it lacks transporters, but sucrose can permeate through a plant cell since transporters are present. As a result of sucrose’s non-permeability in mammalian cells, the isotonicity of isotonic sucrose solution in mammalian cells.
It’s crucial to remember that tonicity is governed only by non-penetrating solutes to grasp this. Hypotonic solutions have a lower concentration of non-penetrating solutes than hypertonic solutions. A 5 percent dextrose solution with no non-penetrating solutes is a classic example of a hypotonic solution.
Water movement occurs when a cell is put in a hyperosmotic yet hypotonic solution, such as 10% dextran. As a result, a solution might be hyperosmotic and hypotonic at the same time.
When the extracellular fluid’s osmolarity exceeds that of the intracellular fluid, the cell is said to be exposed to a hyperosmotic environment and will undergo hyperosmotic stress. When the extracellular fluid has a greater osmolarity, it causes water to flow out of the cell, causing cell shrinkage and finally dehydration.
A cell’s exposure to hyperosmotic fluid can be extremely harmful to it. Such cells will have to cope with water efflux, which will disturb a variety of cellular functions, including DNA synthesis and repair, protein translation and degradation, and mitochondrial dysfunction. The cell shrinks and the nucleus convexes as a result of the hyperosmotic state.
Apoptosis, which leads to cell death, is induced by cell shrinkage. When the extracellular fluid’s osmolarity is less than that of the intracellular fluid, the cell is said to be in a hypoosmotic environment. There will be an influx of water/solvent in such an atmosphere.
Physiological Importance of Hyperosmotic Property
The human body is very adaptable to such changes, and in order to do so, cells engage in osmo-adaptive reactions, in which they attempt to adjust to such changes and restore homeostasis. Failure to re-establish homeostasis, on the other hand, frequently leads to a sick or inflammatory state in the body.
Osmolarity imbalances may be harmful to cells and biological processes, and can even lead to illness. The kidney, in conjunction with the antidiuretic hormone arginine vasopressin (AVP) produced by the posterior pituitary, regulates osmolarity homeostasis in the human body.
The release of AVP from the pituitary gland is triggered by an increase in plasma osmolarity. AVP then works on the kidney, increasing the distal tubule’s membrane permeability and therefore increasing tubular reabsorption of water from the kidney. The kidney controls both the quantity of solute and water in the urine.
The urine output might have a low osmolarity (50 mOsm/L) or a high osmolarity (1200-1400 mOsm/L) depending on the body fluid state. When the body has an overabundance of water and the extracellular fluid has a low osmolarity, low osmolarity urine is produced. The urine is hypoosmotic in this situation.
Hyperosmotic urine, on the other hand, is formed when the body is dehydrated and the extracellular fluid has a high osmolarity. Higher osmolality in body fluids causes the pituitary to produce AVP, which promotes tubular water reabsorption from the kidney.
As a result of water reabsorption, the amount of water in the urine output is decreased, resulting in highly concentrated urine, also known as hyperosmotic urine. Osmolarity changes have also been linked to the initiation of inflammatory processes in the body.
Hypernatremia, heat stroke, diabetes, tissue burns, dehydration, asthma, cystic fibrosis, and uremia have all been linked to high extracellular fluid osmolarity. TNF, IL1, IL6, IL8, and IL18 are pro-inflammatory cytokines that have been linked to hyperosmotic stress-related diseases.
Consider the following example: The tubular fluid in the kidneys is:
1. When it’s at the start of the Henle loop, it’s iso-osmotic (to plasma).
2. When it’s at the end of the loop, it’s hyperosmotic (to plasma).
3. When it departs the loop, it becomes hypo-osmotic (to plasma).
Therapeutic Applications of Hyperosmotics
In the treatment of glaucoma, hyperosmotic drugs are utilised. Glaucoma is a vision or ophthalmic disease in which the intraocular pressure rises (IOP). A rise in IOP, along with impaired vision, is a very unpleasant condition for the patient.
Hyperosmotic drugs lower IOP by creating an osmotic gradient between the blood and intraocular fluid compartments, causing ophthalmic fluid to flow into the bloodstream. When glaucoma does not react to carbonic anhydrase inhibitors given topically or systemically, this treatment strategy is chosen. Hyperosmotic drugs, on the other hand, have a short duration of effectiveness and might cause systemic adverse effects.
IOP is raised in glaucoma due to the presence of vitreous fluid in the eye. The osmolality of the intravascular fluid rises when hyperosmotic drugs are administered (hyperosmolarity).
The ocular barrier, on the other hand, prevents these substances from penetrating into the vitreous fluid. The osmotic gradient is created as a result of this. As a result, fluid from the vitreous outflow enters the vascular fluid. As a result, the patient’s IOP is lowered due to the reduced quantity of vitreous fluid.
The use of hyperosmotic drugs in glaucoma patients has been shown to result in a 3-4 percent decrease in IOP. Molecular weight, dosage, concentration, rate of administration, route of administration, excretion rate, distribution, and ocular penetration are all parameters that influence the effectiveness of these drugs.
Glycerin, urea, isosorbide, mannitol, and other hyperosmotic are examples of hyperosmotic used in glaucoma treatment. These agents can be used topically, intravenously, or orally. However, systemic (parenteral) or oral administration of these drugs may have undesirable side effects.
Hyperosmotic drugs are often used to treat eye illnesses, such as glaucoma, as well as their dosage and possible adverse effects.
Hyperosmotic drugs are also used to improve vision in individuals with corneal edoema, where the agents produce temporary dehydration to reduce the cornea’s oedematous state. Hyperosmotic drugs are also used to treat cerebral edoema, in addition to ocular edoema.
Hyperosmotic drugs can also be used as a plasma volume expander in the treatment of hypovolemic bleeding.
An efficient plasma expander has been reported to be a combination of 7.5 percent sodium chloride and 6 percent dextran-70. This combination of hyperosmotic drugs (NaCl and dextran) has also been shown to decrease acute hypotension and head injury mortality.
The use of a hyperosmotic drug has been shown to have fast cardiovascular effects, including an increase in cardiac parameters such as arterial pressure, cardiac output, plasma volume, cardiac contraction, mean circulatory systemic pressure, and oxygen supply and consumption.
Hyperosmotic Stress in Plants
Plants, like mammals, are susceptible to physiological disturbances caused by hyperosmotic stress. Hyperosmotic stress is a common manifestation in plants as a result of hyperosmotic conditions (when the osmolarity outside is higher than the inside of the cell).
High salt concentrations in the soil, as well as dryness, are the typical culprits. When this happens, the plants respond by changing their genetic expression, producing intracellular osmolytes, and active endocytosis, as well as ion sequestration through vacuolar transport, to counteract the water outflow and subsequent decrease in cell volume.
If the severe disturbance is not corrected quickly, the plant cell may perish due to a loss of turgor pressure and the collapse of the plasma membrane.
- Hyperosmotic stress response: comparison with other cellular stresses. Pflugers Arch . 2007 May;454(2):173-85.
- Response to hyperosmotic stress. Genetics . 2012 Oct;192(2):289-318.
- Hyperosmotic phase separation: Condensates beyond inclusions, granules and organelles. J Biol Chem . Jan-Jun 2021;296:100044.