Mast cell (connective tissue, human)

Electron microscopy. Mast cells (mastocytes) are frequently found perivascularly or perineurally within the connective tissue. A detail of this mast cell shows granules varying in shape and size. These membrane-bound vesicles (so-called compound granules) show a metachromatic reaction in light microscopy and ultrastructurally a granule exhibits a heterogeneous content (different with species). The internal substructure is composed of osmiophilic short parallel stalks (1) in a granular substance appearing in cross-sections as scroll-like or whorl-like figures (2). Scroll-like as well as whorl-like substructures are common in human mastocytes. At thin arrows (↓) the boundaries of some granules. These granules contain among others heparin, histamine, enzymes such as superoxide dismutase, beta-hexosaminidase, tryptase, factors such as neutrophil- and eosinophil-chemotactic factors, vasoactive mediators.