Discovery Fit & Health
Since every part of the human body gets its nutrients from blood, blood truly is the most vital component of human life, and the also the part of the body that's most commonly tested for disease. Your blood has two main components: plasma and formed elements. There are three kinds of formed elements: white blood cells, red blood cells and platelets. The formed elements float in the plasma, which is the liquid part of blood. Plasma circulates throughout the body, carrying not only blood cells, but also other nutrients, vitamins, electrolytes, proteins, hormones and more. Plasma is responsible for distributing all these things where they're needed.
The formed elements also have important jobs to do. Red blood cells contain the protein hemoglobin, which helps them carry oxygen from the lungs throughout the body. The red blood cells also remove carbon dioxide from the body using the enzyme carbonic anhydrase. Red blood cells comprise more than 90 percent of the formed elements in your blood.
White blood cells, also known as leukocytes, are an important part of your immune system. They help your body fight infection by traveling throughout the blood to the site of the problem -- if your blood tests high for white blood cells, you probably have an infection.
Platelets are blood-clotting agents that form in the bone marrow. Platelets don't reproduce, and instead are formed when megakaryocytes, or very large cells, break up into smaller pieces. To help your blood clot, platelets contain a variety of chemicals, including those that help blood vessels repair themselves and those that attract more platelets. Platelets last about 10 days, but more are produced all the time.
A scanning electron microscope image from normal circulating human blood. (Photographers Bruce Wetzel/Harry Schaefer, courtesy National Cancer Institute)
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