TRANSIENT CELLS OF THE CONNECTIVE TISSUE – 2
In addition to resident cells, connective tissue normally contains several types of transient cells. most of them are white blood cells or leukocytes that originate in the blood. They leave the blood capillaries and venules by diapedesis between the endothelial cells that line the blood vessels and penetrate the connective tissue.
Leukocytes are classified under the microscope according to the shape of their nucleus and the granules present in their cytoplasm.
Polymorphonuclear and mononuclear leukocytes
During leukocyte differentiation in the hematopoietic marrow, their nuclei are initially spherical. At the end of the differentiation process of a group of leukocytes, their nucleus becomes lobulated, that is, the nucleus becomes separated into two or more parts called lobules. The lobules are connected by thin “filaments” of chromatin that are visible with an optical microscope. The lobulated leukocytes are also called polymorphonuclear leukocytes (PMNs), and comprises the blood cells called neutrophils, eosinophils, and basophils.
The other group of leukocytes — the lymphocytes and monocytes – do not have lobulated nuclei. Their nuclei remain spherical in the fully differentiated cells. They are also called mononuclear blood cells.
Granulocytes and Agranulocytes
All leukocytes have granules in their cytoplasm. There are two types of granules: unspecific and specific granules.
Nonspecific granules, also called azurophilic granules (due to their color after staining by stain techniques developed to study blood cells with a light microscope). They are present to varying degrees in all types of leukocytes.
Specific granules are present in neutrophils, eosinophils, and basophils. Each of these cells has characteristic granules, with specific sizes, content, and staining features.
The leukocytes that have specific granules in their cytoplasm is also called granulocyte leukocytes, in contrast to lymphocytes and monocytes, which have only nonspecific granules and are also called agranulocyte leukocytes.