Morphology and physiology of salivary myoepithelial cells.

Myoepithelial cells, which occur in many but not all exocrine glands, are usually quite conspicuous in salivary glands. Their contractile nature seems established beyond doubt, and the morphological similarities to smooth muscle cells are close enough to suggest that they contract by a similar, if not the same, mechanism. Morphologically speaking, they seem to possess a dual autonomic innervation, but, functionally speaking, the sympathetic control seems usually to be more important that the parasympathetic. While their contraction undoubtedly causes a transitory increase in the rate of delivery of saliva to the oral cavity, the principal function of the cells seems to be to prevent distension of the endpieces during secretion. This is achieved partly by providing support for the endpiece and partly by a widening and shortening of the intercalated ducts, which has the effect of lowering the outflow resistance.