The fine structure of connective tissue: I. The fibroblast

Abstract

The fine structure of fibroblasts of regenerating tendon, granulation tissue and various other tissues was studied by electron microscopy. The cells were identified as fibroblasts with the light microscope, and then ultrathin sections were prepared for electron microscopy. Fibrcblasts, particularly proliferating ones, are difficult to preserve adequately, swelling and disruption of mitochondria occurring frequently. The findings reported in this paper are based only on the study of adequately preserved material. Fibroblasts as seen by electron microscopy are elongated spindle-shaped or stellate cells, with a slightly indented nucleus. In the resting cell the cytoplasm may taper off into long slender processes. Both resting and proliferating cells contain ergastoplasm (rough-surfaced vesicles of the endoplasmic reticulum), but this is more abundant in proliferating cells. The ergastoplasm sometimes contains an electron dense substance and it may be distended. The periphery of the cell is free of ergastoplasm, but often contains fine filaments. A large Golgi apparatus was always seen in proliferating fibroblasts. Dense, osmiophilic, stellate bodies in the cytoplasm are typical of the fibroblast. Small granules or globules occur in the Golgi region, and somewhat larger ones are found in the periphery of the cytoplasm. Most of the granules resemble secretory granules. Others look like ingested material, or like structures described as lysosomes. A puzzling structure encountered in the Golgi area is a spindle-shaped body containing filamentous material, which stains intensely with phosphotungstic acid.