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.