Morphology of the Haversian canal. An electron microscopic study

Electron microscopic study of the Haversian canal and its content was performed. Four types of wall lining cells were identified: undifferentiated lining cells, resting mature osteoblasts, active osteoblasts, osteoblast-osteocytes which represented different stages in the differentiation process of the fibrilogenetic cell population. The narrow space between the lining cells and the mineralized bone tissue contained randomly oriented collagen fibrils arranged in layers. Such arrangement of the fibrils determined the lamellar model of the osteons prior to their mineralization. The perivascular space contained both poorly differentiated and mature fibrilogenetic cells with numerous cytoplasmic processes as well as collagen fibrils with different orientation. The cells and the fibrils formed networks which were the sites of the metabolic exchange between the blood vessels and the bone tissue. This process was realised in the medium of the interstitial fluid which filled the perivascular space. All these make the perivascular space an important link of the osteon microcirculation.