Lymphocytes:

1. Classified: Small / medium / large. 
2. Medium and large lymphocytes -> In fibrous connective tissue, occasionally in circulation bloodstream. 

Monocytes/Phagocytes:

1. Largest of formed elements. 
2. Cytoplasm -> abundant and relatively clear. 

Granulocytes:

Neutrophils :

1. Contain fine cytoplasmic granules (light microscope)
2. Also called polymorphonuclear (PMN) (variety of nuclear shapes)

Eosinophils:

1. Large granules, prominent nucleus (divided into two lobes)

Basophils:

1. Pale nucleus (usually hidden by granules)

Lymphocytes:

1. Destroy cancer cells, cells infected by viruses, and foreign invading cells. 
2. Antigens to activate other cells of the immune system. 
3. Coordinate the actions of other immune cells, secrete antibodies and serve in immune memory.

Monocytes:

1. Differentiate into macrophages (large phagocytic cells), digest pathogens, dead neutrophils, and the debris of dead cells.
2. Like lymphocytes, they also present antigens to activate other immune cells.

Granulocytes:

Neutrophils :

1. Destroy bacteria and release chemicals that kill / inhibit the growth of bacteria.

Eosinophils:

1. Destroy allergens and inflammatory chemicals, and release enzymes that disable parasites.

Basophils:

1. Secrete histamine -> increases tissue blood flow (dilate blood vessels)
2. Secrete heparin (anticoagulant that promotes mobility of other WBCs by preventing clotting)

They protect the body from infection and foreign cells.