What are the four main components of blood?

Blood has four components: plasma, red blood cells, white blood cells and platelets. Plasma is the liquid component of blood, in which the other three components are suspended. Red blood cells comprise about 40 percent of the blood's volume, while plasma makes up more than half of the volume.

The other two components, white blood cells and platelets, make up a small fraction of the total volume of blood. There are five main types of white blood cells, which are responsible for fighting infection in the body: neutrophils, lymphocytes, monocytes, eosinophils and basophils. Blood contains about one platelet for every 20 red blood cells; platelets assist in the clotting process of the blood.