A study of calcification in the leg tendons from the domestic turkey

Details are presented of the structure and the spatial and temporal sequence of calcification within leg tendons obtained from the domestic turkey, Meleagris gallopavo. Histological and ultrastructural examination of the tissues reveals the development of large tendonoblasts, disposed in columns parallel to tendon long axes. Maturing cells are characterized by organelles active in protein synthesis, few mitochondrial granules, and an extensive system of processes. Deposition of mineral in the extracellular tissue spaces appears initially associated with small vesicular structures located between collagen fibrils. As calcification progresses, mineral is associated predominantly with collagen. Electron diffraction and electron probe microanalysis indicate that the mineral is a poorly crystalline hydroxyapatite having a Ca/P molar ratio ranging between 0.9 and 1.5. Following decalcification and staining of tissue sections, vesicular structures retain integrity by uptake of lead and uranium salts while collagen stains only poorly. Implications of these results are discussed with respect to the physicochemical and biological events of vertebrate calcification.