Blood is a tissue in which highly specialized cells are suspended in a fluid matrix called plasma. Blood serves to transport many diverse substances, from gases, nutrients, and wastes to information bearing molecules such as hormones and antibodies. Histologically, blood is sometimes classified as a specialized form of connective tissue. In stained blood smears, one can quickly distinguish between the oxygen bearing erythrocytes without nuclei and the basophilic, nucleated leukocytes which perform diverse roles in bodily defense. Recognition of the cell types, particularly leukocytes, and the significance of their relative numbers are frequently important in medical diagnoses. Blood in adults is produced in bone marrow and an examination of marrow reveals immature forms of the various blood cells and platelet-producing cells.

Learning Objectives for this unit:

• 
  Learn and identify all types of mature blood cells and platelets by their morphological characteristics.
• Recognize precursors of various blood cells.
• Understand the process of blood cell formation, hemopoiesis, in bone marrow.
• Recognize the structural features and significance of bone marrow

Let's go straight to a blood smear.