Understanding Blood Cells: Types, Functions & Composition

A blood cell may be any of several different types of cells found in the blood. Each blood-cell type performs a specific set of functions. The blood cells only comprise 45 percent of the total volume of blood with plasma comprising the remaining 55 percent.

Erythrocytes

• Erythrocytes are also known as red-blood cells and are the most common type of blood cell in the body, with about five million cells in each cubic millimeter (mm^3) of blood. Their primary function is to carry oxygen from the lungs to the various other cells in the body.

Leukocytes

• Leucocytes are also called white-blood cells and are typically found in a concentration of 6,000/mm^3. Their main function is to attack foreign cells that they find in the body. The white-blood cell count can rise dramatically when the body is fighting an infection.

Granulocytes

• Granulocytes have granules in their cytoplasm and are a type of leukocyte. They specialize in engulfing and digesting foreign particles.

Agranulocytes

• Agranulocytes actually have some granules in their cytoplasm, despite the name. This group of leukocytes plays multiple important roles in the body's immune system.

Thrombocytes

• Thrombocytes, also known as platelets, typically have a density in the blood of 250,000/mm^3. Their main function is to clot the blood by releasing clotting factors such as serotonin and fibrin.