Figure 514

Fibroblasts in connective tissue. Photomicrograph of a connective tissue specimen fixed with glutaraldehyde, embedded in plastic, and stained with H&E. Thin strands of fibroblast cytoplasm (arrow/5) belonging to a few preferentially oriented cells can just barely be recognized between collagen fibers. In routine H&E-stained, paraffin-embedded preparations, it is usually impossible to distinguish the attenuated and poorly preserved fibroblast cytoplasm from the collagen fibers. Typically, only the nuclei of these cells are evident. x600.

replicating population of cells that have a particularly close physical relationship with the overlying epithelium. They are believed to interact with the epithelium in normal renewal and differentiation in the adult organism (epithe-lial-mesenchymal interaction).

The myofibroblast displays properties of both fibroblasts and smooth muscle cells

The myofibroblast is an elongate, spindly connective tissue cell not readily identifiable in routine H&E preparations. With the TEM, the myofibroblast displays typical cytologic characteristics of the fibroblast along with characteristics of smooth muscle cells. In addition to rER and Golgi profiles, the myofibroblast contains bundles of longitudinally disposed actin filaments and dense bodies similar to those observed in smooth muscle cells (Fig. 5.16). As in the smooth muscle cell, the nucleus often shows an undulating surface profile, a phenomenon associated with cell contraction. The myofibroblast differs from the smooth muscle cell in that it lacks a surrounding basal lamina (smooth muscle cells are surrounded by a basal or external lamina). Also, it usually exists as an isolated cell, although its processes may contact the processes of other myofibroblasts. Such points of contact exhibit gap junctions, indicating intercellular communication.

The myofibroblast is implicated in wound contraction, a natural process that results in closure of a wound in which

Myofibroblast Tem
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