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Blood
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Blood

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Summary

Your blood is made up of liquid and solids. The liquid part, called plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets.

Red blood cells (RBC) deliver oxygen from your lungs to your tissues and organs. White blood cells (WBC) fight infection and are part of your immune system. Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones. Red blood cells live about 120 days, and platelets live about 6 days. Some white blood cells live less than a day, but others live much longer.

There are four blood types: A, B, AB, or O. Also, blood is either Rh-positive or Rh-negative. So if you have type A blood, it's either A positive or A negative. Which type you are is important if you need a blood transfusion. And your Rh factor could be important if you become pregnant - an incompatibility between your type and the baby's could create problems.

Blood tests such as blood count tests help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working. Problems with your blood may include bleeding disorders, excessive clotting and platelet disorders. If you lose too much blood, you may need a transfusion.

NIH: National Heart, Lung, and Blood Institute

Start Here

  • Blood (For Parents) (Nemours Foundation) Also in Spanish
  • Blood Basics (American Society of Hematology)
  • Blood Donation FAQs (America's Blood Centers)
  • Blood Tests From the National Institutes of Health (National Heart, Lung, and Blood Institute) Also in Spanish

Diagnosis and Tests

  • What You Need to Know About Blood Testing From the National Institutes of Health (National Library of Medicine) Also in Spanish

Related Issues

  • Cord Blood Testing and Banking From the National Institutes of Health (National Library of Medicine) Also in Spanish
  • Diversity in Blood Types (American Red Cross)

Specifics

  • Blood Types (For Parents) (Nemours Foundation)
  • Facts About Blood and Blood Types (American Red Cross)

Videos and Tutorials

  • Red blood cell production Video (Medical Encyclopedia) Also in Spanish

Test Your Knowledge

  • Play the Blood Typing Game (Nobel Foundation)

Clinical Trials

  • ClinicalTrials.gov: Blood Cells From the National Institutes of Health (National Institutes of Health)

Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)

  • Article: Staphylococcus aureus LukMF' targets neutrophils to promote skin and soft tissue...
  • Article: Potential therapeutic roles of natural killer cells in acute myeloid leukemia:...
  • Article: CAR-T cell therapy in brain malignancies: obstacles in the face of...
  • Blood -- see more articles

Reference Desk

  • Biology of Blood (Merck & Co., Inc.) Also in Spanish
  • Hematology Glossary (American Society of Hematology)

Find an Expert

  • Find a Hematologist (American Society of Hematology)
  • National Heart, Lung, and Blood Institute From the National Institutes of Health

Children

  • What's Blood? Video (Nemours Foundation) Also in Spanish

Teenagers

  • Blood Video (Nemours Foundation) Also in Spanish
  • Blood Types (Nemours Foundation) Also in Spanish

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Blood

MEDICAL ENCYCLOPEDIA

  • Arterial stick
  • Blood typing
  • Capillary sample
  • Cord blood testing
  • Red blood cell production
  • Venipuncture

Related Health Topics

  • Bleeding
  • Bleeding Disorders
  • Blood Clots
  • Blood Count Tests
  • Blood Disorders
  • Blood Transfusion and Donation
  • Platelet Disorders
  • Rh Incompatibility

National Institutes of Health

The primary NIH organization for research on Blood is the National Heart, Lung, and Blood Institute

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The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.

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