Ultrastructural observation of arteriolar calcification in a submandibular salivary gland.

Foci of calcification were found ultrastructurally in the wall of an arteriole of a specimen of chronic submandibular sialadenitis. They were seen in the basement membrane surrounding the smooth muscle cells, where some of them were associated with vesicles and membraneous debris, and in a macrophage. Calcium and phosphorus were detected microanalytically in the calcifications, which contained needle-shaped crystals. The calcifications in the basement membrane may have started in vesicles released from smooth muscle cells and those in the macrophage may have arisen by heterophagy. Matrix vesicles appear to be of significance in arteriolar calcification and macrophages may offer protection against it.