We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.
Biology

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is Oncotic Pressure?

Mary McMahon
By
Updated: May 21, 2024
Views: 79,375
Share

Oncotic pressure is a form of pressure in the circulatory system which encourages water to cross the barrier of the capillaries and enter the circulatory system. In patients with low oncotic pressure, fluid will tend to accumulate in the tissues, resulting in edema. This phenomenon is part of a complex interconnected system which is designed to keep the body in a state of homeostasis, working together with hydrostatic pressure to keep the level of fluids in the blood stable.

The walls of the circulatory system are semi-permeable. Fluids can pass across these membranes, but larger materials such as proteins, also known as colloids, cannot. Hydrostatic pressure is the force which pushes fluids over this membrane and out of the circulatory system, while oncotic pressure is the force which brings fluids back into the circulatory system. When these two forces are in balance, there is no net loss or gain of fluid from the circulatory system. When they are not, a patient can develop medical problems.

Oncotic pressure occurs as a result of osmosis. When fluids move across the membrane of the capillaries due to hydrostatic pressure, they leave behind a concentration of solutes which were too big to cross the membrane. Fluids tend to flow from areas of low concentration to areas of high concentration, which means that when the solute level rises as fluid leaves the capillaries, fluids are pulled across the membrane and into the capillaries to balance the concentration of the solution on both sides of the barrier.

Sometimes, oncotic pressure may be referred to as colloid osmosis or colloid osmotic pressure, referencing the process and solutes involved. A number of things can influence oncotic pressure, including the amount of colloids in the blood. People with imbalanced concentrations of colloids in their blood may be at risk of low oncotic pressure. Individuals suffering from dehydration or an excess of fluids can also develop imbalances in their oncotic pressure as their bodies cannot compensate quickly enough.

Several equations involve oncotic pressure, and there can be medical situations in which it is useful to understand this phenomenon. Doctors and nurses generally learn about oncotic pressure, among a wide variety of other topics, in coursework which covers basic anatomy and physiology, and their studies may include familiarization with equations which involve the various forces which keep the circulatory system flowing evenly and maintain the balance of fluids in the body.

Share
All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All The Science researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By anon1005466 — On Sep 03, 2021

Great explanation. Thank you.

By anon230805 — On Nov 21, 2011

This helped me a lot! Thank you!

By calpat — On Feb 02, 2011

The terms hydrostatic and oncotic pressure are new to me. The only pressure I had ever heard of concerining the human body, is blood pressure. Everyone is always talking about having high blood pressure these days.

All three have to do with the circulatory system though, which makes me wonder if blood pressure is related in some way to the other two.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
Share
https://www.allthescience.org/what-is-oncotic-pressure.htm
Copy this link
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.