Merck Manual

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Overview of Blood

By

Ravindra Sarode

, MD, The University of Texas Southwestern Medical Center

Reviewed/Revised Jan 2024
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Overview of the Blood
VIDEO

Blood is a complex mixture of

The body contains about 5 to 6 quarts (about 5 liters) of blood.

Blood performs various essential functions as it circulates through the body:

  • Delivers oxygen and essential nutrients (such as fats, sugars, minerals, and vitamins) to the body's tissues

  • Carries carbon dioxide to the lungs

  • Carries waste products to the kidneys for elimination from the body

  • Transports hormones (chemical messengers) to allow various parts of the body to communicate with each other

  • Carries components that fight infection and stop bleeding

  • Carries components that stop bleeding

Once blood is pumped out of the heart, it takes 20 to 30 seconds to make a complete trip through the circulation and return to the heart.

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