Science

Difference Between Osmotic Pressure and Oncotic Pressure

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Key Difference

Both these pressures, Osmotic Pressure and Oncotic pressure, are interrelated, one willing to understand both these terms keenly needs to understand the process of Osmosis. Which is the basis of both these pressure and also plays a pivotal role in living organisms, where the transportation of water and other molecules happens across membranes like caterpillars and arteries. Osmosis is the process in which solvent molecules pass through a semipermeable membrane from a less concentrated solution towards the high concentrated solution. Following it, Osmotic Pressure is the minimum pressure required to stop the inward flow of solvent across a semi permeable membrane, on the other hand, Oncotic Pressure aka colloid osmotic pressure, is the type of osmotic pressure in which pressure is applied by albumin and proteins in a blood vessel’s plasma to pull the water into the circulatory system. Osmotic pressure and oncotic pressure here are being discussed with respect to biological movement in the body. Collectively both these terms are referred as ‘Starling Forces’ as they govern the passive exchange of water between the capillary microcirculation and the interstitial fluid.

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Comparison Chart

Osmotic PressureOncotic Pressure
DefinitionOsmotic Pressure is the minimum pressure required to stop the inward flow of solvent across a semi permeable membrane.Oncotic Pressure aka colloid osmotic pressure, is the type of osmotic pressure in which pressure is applied by albumin and proteins in a blood vessel’s plasma to pull the water into the circulatory system.
Measured UsingOsmometerOncometer
FactorsOsmotic pressure is directly proportional to the temperature and the concentration of solute in the solution.Oncotic pressure is directly proportional to the number of colloids in a solution.

What is Osmotic Pressure?

Osmotic Pressure is the external pressure that is required to prevent the inward flow of solvent into the solution separated by the semipermeable membrane. To get the actual sense of this pressure being exerted on solution one should know about the process of osmosis in which solvent molecules pass through a semipermeable membrane from a less concentrated solution towards the high concentrated solution. Pleffers’ Method and Berkeley and Hartley’s Method are the most famous method for determining the osmotic pressure, though now in modern times an apparatus known as Osmometer is also used to determine the osmotic pressure. Osmotic pressure is directly proportional to the temperature and the concentration of solute in the solution, whereas it is inversely proportional to the volume of the solution. Solutions on the basis of atmospheric pressure can be divided mainly into these three types: 1) Isosmotic Solution: The Atmospheric pressure of the solution is equal to the surrounding. 2) Hyperosmotic Solution: The Atmospheric pressure of the solution is higher than the surrounding. 3) Hypoosmotic Solution: The Atmospheric pressure of the solution is lower than the surrounding.

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What is Oncotic Pressure?

Oncotic Pressure aka colloid osmotic pressure, is specifically the type of pressure in biological fluids. Moreover, it is the type of osmotic pressure in which pressure is applied by albumin and proteins in a blood vessel’s plasma to pull the water into the circulatory system. Actually, it is the pressure adding up in the osmolality with the presence of colloids present in a solution. Oncotic pressure is the form of osmotic pressure that is required to prevent the colloidal osmotic flow in body. This pressure plays pivotal role in the maintenance of water balance of bodily tissues. In an animal body, proteins and albumin are responsible for the majority of oncotic pressure as in blood plasma capillaries albumin conducts the 75% the entire oncotic pressure. Oncotic pressure is measured by the oncometer and it is directly proportional to the number of colloids in a solution.

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Osmotic Pressure vs. Oncotic Pressure

  • Osmotic Pressure is the minimum pressure required to stop the inward flow of solvent across a semi permeable membrane, on the other hand, Oncotic Pressure aka colloid osmotic pressure, is the type of osmotic pressure in which pressure is applied by albumin and proteins in a blood vessel’s plasma to pull the water into the circulatory system.
  • Pleffers’ Method and Berkeley and Hartley’s Method are the most famous method for determining the osmotic pressure, though now in modern times an apparatus known as Osmometer is also used to measure the osmotic pressure, whereas oncotic pressure is measured by the Oncometer.
  • Osmotic pressure is directly proportional to the temperature and the concentration of solute in the solution, while oncotic pressure is directly proportional to the number of colloids in a solution.
Harlon Moss

Harlon currently works as a quality moderator and content writer for Difference Wiki. He graduated from the University of California in 2010 with a degree in Computer Science. Follow him on Twitter @HarlonMoss

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