ULTRASTRUCTURAL OBSERVATION OF ARTERIOLAR CALCIFICATION IN A SUBMANDIBULAR SALIVARY-GLAND

Foci of calcification were found ultrastructurally in the wall of an a rteriole of a specimen of chronic submandibular sialadenitis. They wer e seen in the basement membrane surrounding the smooth muscle cells, w here some of them were associated with vesicles and membraneous debris , and in a macrophage. Calcium and phosphorus were detected microanaly tically in the calcifications, which contained needle-shaped crystals. The calcifications in the basement membrane may have started in vesic les released from smooth muscle cells and those in the macrophage may have arisen by heterophagy. Matrix vesicles appear to be of significan ce in arteriolar calcification and macrophages may offer protection ag ainst it.