How Is Osmosis Used in Kidney Dialysis?

Dialysis device with rotating pumps.
Dialysis machine (Image: Andrei Malov/iStock/Getty Images)

Kidney Function

Kidney dialysis is used to replace normal kidney function when the kidneys have become damaged and no longer function properly. The kidneys help control the levels of certain dissolved minerals called electrolytes as well as help filter out waste products (metabolites) that are created by cells using energy. This helps the body maintain stable amounts of compounds such as sodium, potassium and calcium in the blood as well as remove potentially toxic compounds. These toxic compounds are filtered out of the blood and then concentrated by the kidneys into urine, which allows them to be excreted fromt he body. When the kidneys fail, dialysis can be used to take over that function.

Osmosis

Osmosis is a chemical process by which dissolved chemicals will migrate from an area of high concentration to one of low concentration. Essentially if you dissolve something in a liquid, the dissolved compounds (called solutes) will spread out until there is an equal concentration of solute everywhere. Sometimes osmosis works by movement of the solutes until concentration is even everywhere throughout the liquid. However, sometimes osmosis works by having more of the dissolving liquid (called the solvent) move to an area of concentrated solute (to dilute the solute), because this also equalizes the concentration of dissolved solutes.

Osmosis and Dialysis

Kidney dialysis machines use osmosis to take over the filtering function of the kidneys. Dialysis machines use a semi-permeable membrane, which is a membrane through which some small molecules can pass (such as water, salts, and metabolites) but through which larger objects (such as proteins and blood cells) cannot. Dialysis machines take the blood and place a semi-permeable membrane between the blood and a large volume of a liquid called the dialysis solution. Osmosis causes the metabolites to flow out of the blood, through the membrane, and into the dialysis solution, which is continuously replaced. The membrane also allows electrolytes to pass through so that the blood can get rid of extra electrolytes. Consequently, dialysis machines use the power of osmosis to get toxins out of the blood and replace the filtering function of the kidneys.

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