Diffusion and Red Blood Cells

NewsGuard 100/100 Score

Animals breathe in oxygen, following which it must be delivered to all the organs in the body. This process involves red blood cells and diffusion.

Credit: eyeretina/Shuttertstock.com

Red blood cells

Red blood cells (RBCs) are a type of blood cell whose role is to transport oxygen from the lungs to the peripheral tissues of the body. Oxygen diffuses from the alveoli of the lungs into the RBCs, where it binds to hemoglobin. One molecule of hemoglobin can bind four molecules of oxygen (O2).

The partial pressure of oxygen determines the affinity of hemoglobin for oxygen. In the lungs, the partial pressure of oxygen is high, and hemoglobin has a high affinity for oxygen. In other tissues, the partial pressure of oxygen is lower, and hemoglobin releases its oxygen molecules.

This difference in affinities is important for oxygen to be delivered where it’s needed. Red blood cells have the shape of a flattened disk, generating a broad surface area for the diffusion of oxygen. Since their only purpose is carrying oxygen throughout the body, they lack many typical cell structures, including a nucleus.


Red blood cells are filled with hemoglobin. Hemoglobin is a globular protein comprised of four polypeptide chains with an iron-binding group called heme on each chain. The heme group has affinity for oxygen and when oxygen is present it is red, but when it lacks oxygen it is bluish. Hemoglobin also binds waste carbon dioxide for its return to the lungs, but this does not occur at its heme binding site.

Fetal hemoglobin

A developing fetus receives oxygen through the mother’s blood supply. Fetal hemoglobin has a higher affinity for oxygen than maternal blood, in order for oxygen to be successfully transferred from maternal red blood cells through the placenta to fetal red blood cells.

The reason that fetal hemoglobin has a greater affinity for oxygen is that it lacks an ability to interact with 2,3-bisphosphoglycerate (2,3-BPG), which in adult cells reduces the affinity for oxygen. The difference is due to a single amino acid change in the 2,3-BPG binding pocket.

Diffusion within RBCs

The rate at which RBCs can exchange oxygen and carbon dioxide is a measure of the fitness of the cells. In order to exchange gases, the cells undergo a number of steps including gas permeation across the cell membrane and hemoglobin binding. In the case of CO2, the molecules are converted to HCO3- ions and H+ ions.

The HCO3- ions are transported by the anion exchanger, AE1, and the H+ ions are buffered by hemoglobin. Cytoplasmic diffusion within the cell links all of these processes. The efficiency of gas exchange depends on protein-facilitated membrane transport, including transport of HCO3- ions by AE1 and membrane protein-assisted gas permeation.

The flattened shape of RBCs is believed to facilitate gas exchange by increasing the surface area to volume ratio and reducing the path-length for cytoplasmic diffusion, and thereby reducing delays introduced by cytoplasmic diffusion. However, these advantages have been found to be modest.

Further Reading

Last Updated: Feb 26, 2019

Dr. Catherine Shaffer

Written by

Dr. Catherine Shaffer

Catherine Shaffer is a freelance science and health writer from Michigan. She has written for a wide variety of trade and consumer publications on life sciences topics, particularly in the area of drug discovery and development. She holds a Ph.D. in Biological Chemistry and began her career as a laboratory researcher before transitioning to science writing. She also writes and publishes fiction, and in her free time enjoys yoga, biking, and taking care of her pets.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Shaffer, Catherine. (2019, February 26). Diffusion and Red Blood Cells. News-Medical. Retrieved on May 21, 2024 from https://www.news-medical.net/life-sciences/Diffusion-and-Red-Blood-Cells.aspx.

  • MLA

    Shaffer, Catherine. "Diffusion and Red Blood Cells". News-Medical. 21 May 2024. <https://www.news-medical.net/life-sciences/Diffusion-and-Red-Blood-Cells.aspx>.

  • Chicago

    Shaffer, Catherine. "Diffusion and Red Blood Cells". News-Medical. https://www.news-medical.net/life-sciences/Diffusion-and-Red-Blood-Cells.aspx. (accessed May 21, 2024).

  • Harvard

    Shaffer, Catherine. 2019. Diffusion and Red Blood Cells. News-Medical, viewed 21 May 2024, https://www.news-medical.net/life-sciences/Diffusion-and-Red-Blood-Cells.aspx.


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Harvard neuroscientist seeks to capture synapse-level connectome data from a mouse brain