Review of scanning electron and light microscopic methods in microcirculation research and their application in pancreatic studies.

The methods reviewed here include: scanning electron microscopy (SEM) of vascular corrosion casts, SEM of intact tissue, SEM of HCl-collagenase treated tissues, light microscopy (LM) of India ink or silicon rubber injected tissues, with stereomicrography, LM of tissue stained by perfusion with hematoxylin, and a correlative study of intravital microscopy with SEM of vascular corrosion casts or LM of India ink-injected tissue. The last technique allowed for both the examination of the microvascular architecture and blood flow in a particular tissue area. This paper shows that an adequate understanding of the microvasculature of the pancreas can only be gained when a variety of SEM techniques, together with other LM and TEM techniques are employed in a coordinated fashion. The intralobular arterioles of the pancreas supply the islets of Langerhans, exocrine acini, and duct system. Blood leaving the islets flows into the capillaries in the exocrine region through the insulo-acinar portal system and insulo-ductular portal system, although some fraction of the blood drains through venules into nearby veins. Thus, these studies in the pancreas indicate that the islets of Langerhans are situated in the center of the pancreatic microcirculatory bed so that the insular secretions are transferred in high concentrations through short vascular routes to the exocrine region of both the duct system and acini, presumably to act upon these structures.