Merck Manual

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Overview of Blood Disorders

By

David J. Kuter

, MD, DPhil, Harvard Medical School

Reviewed/Revised Sep 2023
VIEW PROFESSIONAL VERSION

Some blood disorders cause the number of cells in the blood to decrease:

Other blood disorders cause the numbers of blood cells to increase:

Other blood disorders affect proteins within the blood cells or blood plasma Plasma The main components of blood include Plasma Red blood cells White blood cells Platelets read more Plasma (the liquid portion of the blood):

Blood flows to every cell in the body and is important to the health and function of all of the body's organs.

Blood cells are produced in the bone marrow, and many blood proteins are made in the liver or the blood cells themselves. Blood cells and blood proteins provide the following functions:

  • Red blood cells contain hemoglobin, which carries oxygen to every part of the body.

  • White blood cells and antibodies fight infections and cancers.

  • Platelets and blood clotting factors make bleeding stop or prevent bleeding from occurring.

NOTE: This is the Consumer Version. DOCTORS: VIEW PROFESSIONAL VERSION
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