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blood
References & Edit History Related Topics
Images & Videos
Blood plasma
Observe a red blood cell as it travels from the heart to the lungs and other body tissues
Function of red blood cells explained
Gloved hands hold a blood sample tube above a rack of vials in a laboratory, illustrating blood analysis in human body science.
Close-up of a medical blood bag filled with red blood, showing attached tubes and connectors against a blurred background.
Illustration of a blood vessel with a cutaway view showing red blood cells, white blood cells, platelets, and plasma, each labeled to highlight the main components of blood. Close-up illustration of multiple human red blood cells with their characteristic disc shape, floating against a red background. Diagram of the hemoglobin tetramer showing two alpha and two beta subunits, each in a different color, with four heme groups labeled, each containing a central iron atom for oxygen binding.
Learn about sickle cell anemia and blood behavior in sickle cell patients
Labeled illustration of a macrophage showing its internal organelles and the process of engulfing and digesting bacteria, with bacteria drawn outside and inside the cell as it undergoes phagocytosis.
At a Glance
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blood summary
Quizzes
Superficial arteries and veins of face and scalp, cardiovascular system, human anatomy, (Netter replacement project - SSC)
The Human Body
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blood: References & Edit History

Additional Reading

Further information on human blood is found in the textbooks Marshall A. Lichtman et al. (eds.), Williams Hematology, 9th ed. (2016); and Ronald Hoffman et al. (eds.), Hematology: Basic Principles and Practice, 6th ed. (2013). Shauna C. Anderson and Keila Poulsen (eds.), Anderson’s Atlas of Hematology (2013), offers a complete set of color photomicrographs of blood cells. The biochemical mechanisms involved in bleeding and blood clotting are covered in Victor J. Marder et al. (eds.), Hemostasis and Thrombosis: Basic Principles and Clinical Practice, 6th ed. (2013).

The Editors of Encyclopaedia Britannica

Article Contributors

Primary Contributors

  • C. Lockard Conley
  • Robert S. Schwartz
    Professor of Medicine, Tufts University, Boston; former Chief, Division of Hematology-Oncology, New England Medical Center.
  • The Editors of Encyclopaedia Britannica
    Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.

Other Encyclopedia Britannica Contributors

Article History

Type Description Contributor Date
Invalidated site: Hektoen International - Anne McLaren, transfusion, transplantation, and the nature of blood. Nov 06, 2026
Add new Web site: Interesting Facts - Mosquitos May Prefer a Certain Blood Type. Aug 07, 2026
Add new Web site: Johns Hopkins Medicine - Facts About Blood. Apr 13, 2026
Cross-references added. Nov 07, 2025
Add new Web site: Biology LibreTexts - Blood. Sep 22, 2025
Cross-references added. Apr 18, 2025
Add new Web site: Thompson Rivers University - Human Biology - Blood. Mar 27, 2025
Add new Web site: MSD Manual - Consumer Version - Overview of Blood. Jul 22, 2024
Media added. Mar 12, 2024
Media added. Feb 22, 2024
Add new Web site: Hektoen International - Anne McLaren, transfusion, transplantation, and the nature of blood. Nov 02, 2023
Add new Web site: Khan Academy - Components of blood. Oct 13, 2023
Add new Web site: Cleveland Clinic - Blood. Aug 13, 2023
Add new Web site: Healthline - Blood Typing. Mar 31, 2023
Add new Web site: Openstax - Anatomy and Physiology 2e - An Overview of Blood. Oct 20, 2022
Add new Web site: University of Rochester Medical Center - Health Encyclopedia - Facts about blood. Apr 04, 2022
Media added. Oct 24, 2020
Add new Web site: Idaho Public Television - Blood. Jul 19, 2018
Add new Web site: National Center for Biotechnology Information - What does blood do? Mar 29, 2018
Media added. Jul 07, 2017
Bibliography revised and updated. Jul 07, 2017
Cross-references added. Jul 07, 2017
Media added. Apr 29, 2016
Add new Web site: WebMD - Blood. Feb 20, 2013
Add new Web site: Untamed Science - Blood. Sep 12, 2012
Add new Web site: Science Kids - Fun Science and Technology for Kids - Health Facts. Mar 16, 2012
Added new Web site: How Stuff Works - Health - How Artificial Blood Works. Jul 31, 2008
Added new Web site: How Stuff Works - Health - Most Common Blood Types. Jul 31, 2008
Added new Web site: How Stuff Works - Health - How Blood Works. Jul 31, 2008
Added new Web site: The Franklin Institute - Blood. May 14, 2008
Added new Web site: The Nemours Foundation - For Teens - Blood. May 09, 2008
Added new Web site: The Nemours Foundation - For Parents - Blood. Apr 23, 2008
Bibliography revised. Jan 25, 2007
Article revised and updated. Jan 25, 2007
Added new Web site: The Franklin Institute Online - The Heart: An Online Exploration. Jun 06, 2006
Added new Web site: Lifeblood. May 31, 2006
Article revised. Feb 16, 2001
Article revised. Jul 26, 1999
Article added to new online database. Jul 20, 1998
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