White Blood Cells (WBCs)

• Leukocytes, or white blood cells (WBCs), are found circulating within the blood vessels of the cardiovascular system and scattered throughout peripheral tissues
• Leukocytes are divided into two groups based on the presence or absence of cytoplasmic granules

  • granular leukocytes, or granulocytes
  • agranular leukocytes, or agranulocytes
• Lymphopenia means too few lymphocytes, lymphocytosis means too many lymphocytes
• When body cells are infected or damaged, they release chemicals into the interstitial fluids that attract leukocytes
• The attraction to chemical stimuli is called chemotaxis
• Crossing the endothelial lining of a capillary by squeezing between adjacent endothelial cells in a process called diapedesis or emigration