WBCs can be divided into two groups: mononuclear cells and polymorphonuclear cells with granular cytoplasm, also known as granulocytes. WBCs are involved in the body's defense mechanisms against infection.
The cell shown in the upper image is a mononuclear cell, in this case a monocyte. The cell shown in the lower image is a granulocyte, in this case a neutrophil. These cells will be presented in much more detail later.