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:

• Understand that blood is a connective tissue with “formed elements” (cells and platelets) in a fluid matrix (plasma.
• Understand the morphology and function of red blood cells or erythrocytes and the role of the spectrin membrane skeleton in maintaining their biconcave shape and flexibility.
• Understand the relative numbers of the various types of white blood cells or leukocytes in the blood of normal adults and know the major functions of each type.
• Understand that all leukocytes display cell motility and function in secretion, phagocytosis, etc. primarily in the extracellular matrix of tissues after migrating across the blood vessel wall (diapedesis).
• Be able to recognize and find neutrophils, eosinophils, basophils, monocytes, and platelets in a blood smear.
• Understand and recognize the compartments and tissues in blood marrow.
• Understand the developmental sequence and recognize the intermediate cells in the formation of red blood cells and the three types of granulocytes.
• Be able to recognize megakaryocytes and understand how platelets are formed and released.

Let's go straight to a blood smear.