Difference between Osmosis and Dialysis

Key Difference: Osmosis is a type of diffusion, where molecules mix through a semi-permeable membrane to a more concentrated solution from a more dilute solution.  Dialysis is a medical process that helps perform the functions of a kidney when the kidneys are no longer able to work.

There are certain processes that happen in a human body which are necessary for the survival of the human. Osmosis, diffusion, respiration, etc. are a few of these processes. Osmosis takes place inside the cells, where cells absorb and diffuse nutrients by passing them through a semipermeable membrane. The kidney is an organ that performs the important job of maintaining equilibrium in the body by filtering blood and liquid in the body and separating excess water and waste from it. It also functions as a part of the endocrine system. Dialysis is a medical procedure that is required when the kidneys are no longer able to function properly.

 Osmosis is a type of diffusion, where molecules mix through a semipermeable membrane to a more concentrated solution from a more dilute solution. A semi-permeable membrane is a barrier that only allows certain substances to pass through blocking all others. A cell wall is a semi-permeable membrane as it allows water and certain substances diluted in water to pass through. Osmosis requires water in order to be able to pass through the membrane. The transport of substances is also to equalize the solution concentration on both sides of the membrane. Osmosis can also refer to a physical process in which solvents moves across a semi-permeable membrane, which effectively separates the solvent from the solute resulting in two different solutions of different concentrations. This is known as reverse osmosis.

Osmosis is divided into three stages: hypotonic, isotonic and hypertonic. In hypotonic, the external solution is less concentrated than the internal solution, while in hypertonic, the external solution is more concentrated than the internal solution. Isotonic is the equilibrium that is reached when both the solutions have the same concentration. Osmosis is used by various cells and organisms in order to achieve equilibrium. Cells also use osmosis in order to acquire nutrients and energy form water-based solutions into the cell. The cell membranes act as a semi-permeable  passage, allowing large and polar molecules, such as ions, proteins, and polysaccharides to pass through while blocking non-polar and/or hydrophobic molecules such as lipids, small molecules like oxygen, carbon dioxide, nitrogen, nitric oxide, etc. The permeability of the cell membrane depends on solubility, charge, or chemistry, as well as solute size.

The word "osmosis" is derived from words "endosmose" and "exosmose", coined by French physician René Joachim Henri Dutrochet. A practical example of osmosis is a cell, when placed in a high concentrated solution (salt water), will release water from the cell to the medium around it, resulting it in shrinking. However, if it is placed in a lower concentration solution such as fresh water, the cell will absorb the water and grow bigger. Osmosis is also the primary way that plants acquire water and necessary nutrients for survival from the ground. The process of absorbing water from the soil is osmosis.

Dialysis is a medical process that helps perform the functions of a kidney when the kidneys are no longer able to work. The term has been derived from the Greek word ‘dialusis’ meaning “dissolution”. The term has been made by combining ‘dia’ meaning “through” and ‘lysis’ meaning “loosening or splitting”. It is an artificial replacement when the kidney functions are lost, which can be gradual or instant. Dialysis helps by separating the waste and excess water from the blood. It can also be used partially for people that are applicable for a kidney transplant. Dialysis is used when a person experiences around 85-90% loss of their kidney function.

The purpose of the dialysis is to maintain the equilibrium of the body. It does this by removing waste, salt and excess water to keep them from building up in the body, maintains a certain level of chemicals and nutrients (i.e. potassium, sodium, chloride, calcium, phosphorus, magnesium and sulfate) in the body and also helps control the blood pressure. The kidney is also part of the endocrine system and produces erythropoietin and calcitriol, which help in the production of the red blood cells and bone formation, respectively. The first working dialysis machine was developed in 1943 by Dutch physician, Dr. Willem Kolff. However, the first success story happened in 1945. The machine was made using sausage casings, beverage cans, a washing machine and other objects that were available at that time.

Dialysis uses principles such as diffusion and ultrafiltration of fluid across a semi-permeable membrane. In dialysis, the blood flows to one side of a semi-permeable membrane and a dialysate flows by the opposite side. The semi-permeable membrane has tiny holes that allow substances from the blood to diffuse through the membrane to the dialysate. The clean blood is then reinserted back into the body. There are five types of dialysis, of which three are primary and two are secondary. The primary ones are hemodialysis, peritoneal dialysis and hemofiltration, while the secondary ones are hemodiafiltration and intestinal dialysis.

In hemodialysis, the patient’s blood is pumped through the blood compartment of a dialyzer and the other compartment has the dialysate. These are divided by synthetic hollow fibers, which act as the semipermeable membrane. The cleaned blood is then returned back to the body. This is a 3-5 hour process and must be done three times a week. In peritoneal dialysis, the blood is cleaned inside the body itself through a tube that is placed inside the peritoneal cavity in the abdomen. The cavity is filled with dialysate through a surgically placed catheter, where it remains and cleans the arteries and veins. The extra fluid and waste is then removed through the same catheter and discarded. Each exchange takes around an hour to an hour and half and the dialysate must be changed four to five times a day. Hemofiltration is a similar process to hemodialysis, but instead of dialysate it is done by using pressure. Hemodiafiltration is a combination of hemodialysis and hemofiltration. In intestinal dialysis, the patients diet is supplemented with soluble fibers or the patient is required to consume around 1 – 1.5 liters of non-absorbable solutions of polyethylene glycol or mannitol every fourth hour.





Dialysis is the process of removing waste and excess water from the blood when the kidney is no longer able to perform these duties.

Osmosis is the movement of particles or solvent molecules through a partially permeable membrane into a high concentration area from a low concentration area.


There are two main types of dialysis: Internal and external. The process of filtering the blood can happen internally through Peritoneal dialysis or externally via Hemodialysis. Both use machines in order to perform the jobs of the kidneys.

Osmosis occurs primarily with water and cells. If the medium that surrounds the cell has higher water concentration, the cell will absorb the water.


Dialysis helps perform the job of the kidneys when it is unable to perform such duties. It helps maintain the body's internal equilibrium of water and minerals along with separating waste from the blood.

Osmosis allows cells to absorb many nutrients that are available in the water.


Requires water along with other fluids to perform its duty.

Requires water.

Concentration Gradient

Maintains or establishes a new concentration gradient.

Moves down concentration gradient


Requires external energy and pressure from machines.

Passive, as no external energy is needed.


Hemodialysis, Peritoneal dialysis, Hemofiltration, Hemodiafiltration and Intestinal dialysis.

Reverse Osmosis, Forward Osmosis

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