Image: human blood. Hematoxylin and eosin staining.
Erythrocytes: it is the most abundant cell type in the blood. In most mammals, erythrocytes lack a nucleus. Erythrocytes are specialized in transporting oxygen and carbon dioxide.
Neutrophils: they are the most abundant granular leukocytes (60 - 70 % of leukocytes). Neutrophils can be easily recognized by their multilobed nucleus. They show azurophilic granules and many specific granules with lysozimes, complement activators and colagenases. Neutrophils are major players in the defense of bacteria infections.
Lymphocytes: they are the second most abundant leukocytes (20 - 30 % of leukocytes). They are small cells, with some cell size variability. Lymphocytes A and T are the two major types of lymphocytes. Both are involved in the immune responses.
Monocytes: they are large cells with a kinda-shaped nucleus. Monocytes contribute to the defense response of the organism. They exit the blood stream, move to the infection or damaged region, and become macrophages.
Eosinophils: they are granular leukocytes (2 - 5 % of leukocytes) with a bi-lobed nucleus and showing many granules in the cytoplasm, which are strongly staining with acid dyes like eosin. The granules contain basic substances, such as the mayor basic protein and eosinophilic cationic protein. Eosinophils are involved in the defense against parasite infections. They also release histaminases
Basophils: they are the less abundant (about 0.5 % of leukocytes) and the smallest leukocytes. They show a slightly lobed nucleus. Basophils show many specific granules in the cytoplasm that are stained with basic dyes, such as hematoxylin. The granules contain heparin and histamine. They also show receptors for immunoglobulin E, which suggests a cooperation with mastocytes in the defense responses.
Plaquetas: son pequeñas porciones de citoplasma sin núcleo. Su principal misión es cooperar en la aglutinación y coagulación sanguínea. Están presentes en los mamíferos, pero no en los vertebrados inferiores. Se forman mediante desgajes del citoplasma de unas células denominadas megacariocitos que se encuentran en la médula ósea.