Mast cells are

Mast cells

Mast cells are - like macrophages, lymphocytes and eosinophils - in demand when something goes wrong in the connective tissue. Quite a few of them are present in healthy connective tissue as they stand on guard and monitor the local situation. The cytoplasm of mast cells is filled by numerous large vesicles. Mast cells discharge the contents of these vesicles if they come in contact with antigens, for example, proteins on the surface of an invading bacterium or, in allergic reactions, in response to antigens found, for example, on the surface of pollen grains.

The most prominent substances contained in the vesicles are heparin and histamine. They increase blood flow in close by vessels and the permeability of the vessel walls to plasma constituents and other white blood cells. By facilitating access to the area, mast cells facilitate an immune response to the antigen which triggered the release histamine and heparin.

Other connective tissue cells

Lymphocytes and plasma cells

Lymphocytes are usually small cells (6 - 8 µm). Their nuclei are round and stain very dark. The cytoplasm forms a narrow rim around the nucleus and may be difficult to see. There are many of them in the connective tissue underlying the epithelia of the gastrointestinal tract but usually much fewer in other connective tissues. Again, this situation may change - in this case with immunological reactions. Some lymphocytes may differentiate into plasma cells. Plasma cells are lymphocytes which produce antibodies. To accommodate the necessary organelles for this function the size of the cytoplasm increases dramatically and the cells become basophilic. Plasma cells can occasionally be spotted in the loose connective tissue present in sections.
Like eosinophilic cells and monocytes, lymphocytes are white blood cells.

Eosinophilic cells

Eosinophilic cells are typically rounded or oval, large cells, which contain large amounts of bright red granules in their cytoplasm. They originate, like the monocytes, in the bone marrow. They enter connective tissues early in inflammatory reactions, where they phagocytose antigen-antibody complexes. Their numbers in healthy connective tissue vary with location, but a few of them can usually be found.

Mesenchymal cells

During development, mesenchymal cells give rise to other cell types of the connective tissue. A small number of them may persist into adulthood. Mesenchymal cells are smaller than fibrocytes and difficult to detect in histological sections. They may regenerate blood vessels or smooth muscle which have been lost as a consequence of tissue damage.

Suitable Slides

sections of  tongue, skin, mesenteryor other sections containing epithelia and / or loose connective tissue - toluidine blue, cresyl violet

Mast Cells, Tongue - toluidine blue and Mesentry, Rat  - cresyl violet Mast cells are relatively frequent in the connective tissue benath the epithelium and between the muscle fibres of the tongue. In most connective tissue cells and the muscle fibres only the nucleus is stained by the toluidine blue. The cytoplasm of the mast cells is however filled with dark, blue / violet grains which represent their secretory vesicles. At low magnification mast cells stand out as large, dark dots among smaller and lighter stained nuclei and among the very weakly stained remaining connective tissue components. Draw a few mast cells in situ and label both the mast cells and some of the surrounding tissue components.