In vivo microscopy of the exocrine pancreas

Light microscopic studies of the living acinar pancreas, although limited in number, have revealed valuable information concerning dynamic aspects of microvascular and parenchymal structure and function. For example, it has been found that: 1) the living organ in anesthetized animals can be imaged with a resolution approaching the limit of the light microscope; 2) blood flow through individual capillaries in the exocrine pancreas is intermittent; 3) blood flow through these capillaries is regulated locally by smooth muscle precapillary sphincters and within individual capillaries by endothelial cells which are spontaneously contractile as well as responsive to vasoactive substances; and 4) the formation and release of zymogen granules occurs within 45-90 minutes in acinar cells stimulated with pancreozymin. This paper reviews these studies and some of the methods used to obtain them.