Blood is a liquid in humans and many animals. There are about 5 litres of blood in the human body.[1] Blood is pushed through the organism by the heart. It brings nutrients and oxygen to the tissues of the body. It also takes away waste and carbon dioxide from tissues.[2]
Blood is made up of blood plasma and various cells. These include red blood cells, white blood cells and platelets. Platelets help blood to clot. Hemoglobin is in red blood cells. White blood cells help fight infections and heal wounds.
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