Difference Between Osmosis and Dialysis

The main difference between osmosis and dialysis is that the osmosis is the movement of water across a semi-permeable membrane whereas the dialysis is the separation of excess water and smaller molecules from the blood. 

Osmosis and dialysis are two methods involved in the movement of molecules across membranes. Furthermore, the osmosis mainly occurs through the plasma membrane while the dialysis is a medical procedure that substitutes the normal function of the kidney. Moreover, both osmosis and dialysis can be performed artificially in the laboratory.

Key Areas Covered

1. What is Osmosis
     – Definition, Process, Importance
2. What is Dialysis
     – Definition, Process, Importance
3. What are the Similarities Between Osmosis and Dialysis
     – Outline of Common Features
4. What is the Difference Between Osmosis and Dialysis
     – Comparison of Key Differences

Key Terms

Dialysis, Endosmosis, Exosmosis, Intermittent Hemodialysis (IHD), Kidney, Osmosis, Peritoneal Dialysis (PD), Semi-Permeable Membrane,

What is Osmosis

Osmosis is the movement of water molecules across a semi-permeable membrane through a potential gradient. Since osmosis mainly occurs in the cell during the uptake and removal of water from the cell, water molecules move across the plasma membrane, which is semi-permeable. The movement occurs from a higher water potential to the lower water potential. Based on the direction of movement of water into the cell, osmosis can be divided into two types as endosmosis and exosmosis.

Figure 1: Effect of Different Solutions on Blood Cells

• Endosmosis – It is the movement of water into the cell, which occurs when the cell is placed in a hypotonic solution. Hypotonic solutions have a higher water potential when compared to the cytosol. But, sometimes, due to the excess filling of water into the cell, animal cells, which lack a cell wall, may break open.
• Exosmosis – It is the movement of water out of the cell, which occurs when the cell is placed in a hypertonic solution. Hypotonic solutions have a lower water potential when compared to the cytosol. Due to the loss of too much water, the cell may shrink.

The water movement only remains until the two water potentials become equal on both sides of the cell membrane.

What is Dialysis

Dialysis is the main process in the body to remove excess water and solutes from the body. Generally, the kidney is the organ responsible for the removal of excess water, ions, metabolic wastes, and toxins. It filters around 180 L of fluid per day. This means dialysis is applicable when the kidneys fail to perform their normal function. It is also called renal replacement therapy (RRT). A person with 85-90% lost kidney function is eligible for dialysis. The two main types of dialysis are:

• Intermittent Hemodialysis (IHD) – In hemodialysis, blood circulates out of the body with the help of a catheter that passes through a filter. The filter can perform a similar function to the kidney, removing excess water, solutes as well as toxins from the blood. The dialyzed blood enters the body through a vein. Hemodialysis should be performed three times per week.
  

  Figure 2: Hemodialysis

• Peritoneal Dialysis (PD) – In PD, a sterile dialysate solution is inserted into the peritoneal cavity through a tube. This solution is rich in glucose, minerals. The peritoneal cavity is surrounded by the peritoneum, which is semi-permeable. The dialysate absorbs wastes through the peritoneum by diffusion. The high glucose concentration in the dialysate causes osmotic pressure, which in turn moves fluids from blood to the peritoneal cavity. This procedure can be repeated several times per day.

Similarities Between Osmosis and Dialysis

• Osmosis and dialysis are two methods of movement of fluids across semi-permeable membranes.
• Both are involved in the movement of molecules through a gradient.
• Hence, they are passive transportation methods.
• Water molecules move in both processes.
• Both are natural processes that can also be performed under laboratory conditions.

Difference Between Osmosis and Dialysis

Definition

Osmosis refers to a process by which water molecules of a solvent tend to pass through a semi-permeable membrane from a less concentrated solution to a more concentrated one while dialysis refers to the clinical purification of blood as a substitute for the normal function of the kidney. This is the basic difference between osmosis and dialysis.

Mechanism

Mechanism of action is another difference between osmosis and dialysis. Osmosis is the diffusion of water molecules while dialysis can occur through either diffusion or filtration.

Type of Molecules

Furthermore, water molecules move in osmosis while water molecules, solutes, metabolic wastes, and toxins move in dialysis.

Type of Semi-permeable Membranes

One other difference between osmosis and dialysis is the type of the membrane involved in these processes. Osmosis occurs through the cell membrane while dialysis can occur through the peritoneum.

Types of Solvents Involve in

Moreover, cytosol and extracellular fluid are involved in osmosis while blood and dialysate are involved in dialysis.

Types

The two types of osmosis are endosmosis and exosmosis while the two main types of dialysis are hemodialysis and peritoneal dialysis.

Conclusion

Osmosis is the movement of water molecules through a potential gradient of water across the cell membrane. On the other hand, dialysis is a medical procedure, which substitutes the normal function of the kidney by filtering out excess water, solutes, and metabolic wastes from the blood. The main difference between osmosis and dialysis is the mechanism and importance.

Reference:

1. “Osmosis.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 19 Sept. 2017, Available Here
2. Nordqvist, Christian. “Dialysis: All You Need to Know.” Medical News Today, MediLexicon International, 17 July 2018, Available Here

Image Courtesy:

1. “Osmotic pressure on blood cells diagram” By LadyofHats – did it myself based on [1], [2] ,[3] and [4]. (Public Domain) via Commons Wikimedia 
2. “Hemodialysis-en” By GYassineMrabetTalk✉This W3C-unspecified vector image was created with Inkscape. – Own work from Image:Hemodialysis schematic.gif. (CC BY 3.0) via Commons Wikimedia