Blood
(Canadian Campbell 2nd ed, Concept 42.4 & Fig 42.19)

Blood is a tissue in which the extracellular matrix, the plasma, is a liquid. The cellular components are the erythrocytes and the leucocytes, the former outnumbering the latter 600 to 1. Erythrocytes, or red blood corpuscles, contain the respiratory pigment hemoglobin and have an orange tint when seen under the microscope; leucocytes, or white cells are colorless. Remember, however, that you are studying stained slides.

Erythrocytes:

Note the enucleated erthrocytes in a stained slide of human blood. Human erythrocytes are all very close to 7.2mm in diameter. Their size remains constant so that these cells can be used as built-in scales for estimating the size of other cells. Again, the main function of erythrocytes is to transport oxygen throughout the body.

Leucocytes:

Leucoytes contain no pigment and are colorless in unstained preparations. They usually do not have a constant shape because of their capacity of amoeboid movement. They are differentiated from the erythrocytes by the following characteristics: they are larger, they possess nuclei in all vertebrates, hemoglobin is not present in their cytoplasm and they are capable of migration into other tissues of the body. Collectively, the leucocytes function to fight infection. The leucocytes may be divided into two main groups, the granulocytes (neutrophils) which have granules in their cytoplasm and the agranulocytes (lymphocytes and monocytes) which do not. Neutrophils comprise 65-75% of the total leucocytes in the blood, while lympocytes are lower at 20-25% and monocytes lower still, at 3-6% of the total.

Examine the following stained blood smears:

• Human Blood
  • Neutrophil
  • Lymphocyte
  • Monocyte