Difference Between Dialysis and Ultrafiltration

The key difference between dialysis and ultrafiltration is that the dialysis is an artificial process of blood filtration that aids patients suffering from kidney failures while the ultrafiltration is one of the three steps of natural blood filtration that occurs in our kidneys.

In order to reduce the threat of the harmful by-products accumulating in our body via metabolic processes, our excretory system functions efficiently and immediately remove them from our body. Through exhalation, some products go out while some go out through our skin via sweating. Other than those methods, kidneys play a big role in the excretory function. Hence, kidneys are responsible for the maintenance of the body homeostasis.

Not only the waste material but also kidneys remove all the other excess substances such as water, glucose, vitamins, etc. Kidneys filter blood and form urine. Urine formation primarily occurs in the nephrons, which are the functional units of the kidneys. Thus, each kidney consists of millions of nephrons. In nephrons, urine formation occurs via ultrafiltration, reabsorption and secretion. However, due to various disease conditions, kidneys can fail to function properly and filter blood. In those medical conditions, the process called dialysis helps patients to purify their blood.

CONTENTS

1. Overview and Key Difference
2. What is Dialysis
3. What is Ultrafiltration
4. Similarities Between Dialysis and Ultrafiltration
5. Side by Side Comparison – Dialysis vs Ultrafiltration in Tabular Form
6. Summary

What is Dialysis?

Dialysis is a process that helps patients suffering from kidney failures. When the kidneys fail to functions naturally and filter blood in order to form urine and excrete waste, various harmful substances such as toxins, drugs, poisons, etc., accumulate within our bodies. It can eventually lead to fatal conditions. In these situations, dialysis is one of the medical processes that can perform to purify blood and aid in the excretory process. Hence, in simple words, dialysis is an artificial way of replacing the kidney functions. Through dialysis, small solute molecules separate from the larger solutes due to the difference in their diffusion rates. It occurs via a semi-permeable membrane.

There are two main types of dialysis namely hemodialysis and peritoneal dialysis. In hemodialysis, an artificial kidney or a dialysis machine is used to purify the blood. On the other hand, peritoneal dialysis does not use a machine. Instead, it uses a dialysate and the membrane lining of our abdomen in order to clean our blood.

What is Ultrafiltration?

Ultrafiltration is one of the three processes occurring in our kidneys during the blood filtration. Thus, it is the first step that takes place at the Bowman’s capsule. Blood filters from glomerulus to the Bowman’s capsule of the nephron through ultrafiltration. The glomerulus is the capillary network that brings blood with waste material into the Bowman’s capsule. Then blood filters under high pressure. Accordingly, most of the substances in the blood (except globular proteins, red blood cells, white blood cells and platelets) enter into the nephron. The afferent arteriole brings blood in while efferent arteriole takes blood out from the glomerulus.

The pressure needed for ultrafiltration develops due to the diameter difference between the afferent (incoming) and efferent (outgoing) capillaries of the glomerulus. The diameter of the efferent arteriole is less than the afferent arteriole, increasing the blood pressure and causing it to be filtered. Likewise, the filtration takes place between the membranes of the capillaries and the inner membrane of the Bowman’s capsule. This phenomenon, where filtration is taking place under high hydrostatic pressure through a semi-permeable membrane is the process of ultrafiltration.

Not only in kidneys but this can also be simulated in external environments to separate substances from a mixture especially in industries in order to purify solution mixtures and concentrate them. Furthermore, the principal of ultrafiltration is used in water purification processes as well.

What are the Similarities Between Dialysis and Ultrafiltration?

• Dialysis and ultrafiltration are two processes that relate to our kidney function.
• In both processes, waste materials in our blood filter out through a semi-permeable membrane.
• Both processes prevent larger molecules to pass through a membrane.
• These processes have industrial applications as well.

What is the Difference Between Dialysis and Ultrafiltration?

Dialysis and ultrafiltration are two important processes. The key difference between dialysis and ultrafiltration is the process. Dialysis is a clinical application that helps patients to clean their blood artificially while the ultrafiltration is a process that occurs naturally during the urine formation in our kidneys. Furthermore, in dialysis, solutes move from high concentration to low concentration along the electrochemical gradient. But in ultrafiltration, the substances travel due to a pressure gradient. Hence, this is another difference between dialysis and ultrafiltration. Moreover, dialysis occurs in a dialyzer or the membrane lining of our abdomen while ultrafiltration takes place between the glomerulus and the Bowman’s capsule of the nephron.

Furthermore, the rate of ultrafiltration depends on the porosity of the membrane and the speed of blood flow (or the pressure created by the blood flow) while the dialysis rate depends on the dialysate flow rate. Thus, this is also a difference between dialysis and ultrafiltration.

Summary – Dialysis vs Ultrafiltration

Dialysis is a treatment that filters and purifies the blood using a machine. It is a medical procedure. On the other hand, ultrafiltration is a natural process that takes place in our kidneys. It occurs between glomerulus and Bowman’s capsule of the nephrons. Therefore, this is the key difference between dialysis and ultrafiltration.

Reference:

1.“Dialysis Overview.” Fresenius Kidney Care. Available here 
2.“Renal Physiology: Glomerular Filtration.” Khan Academy, Khan Academy. Available here  

Image Courtesy:

1.”Patient receiving dialysis 03″By Anna Frodesiak – Own work, (CC0) via Commons Wikimedia  
2.”Physiology of Nephron”By Madhero88 – Own work, (CC BY 3.0) via Commons Wikimedia