Three-dimensional observation of the rat endocrine pancreas by a scanning electron microscope

A three-dimensional observation was performed on chemically digested rat pancreata and vascular corrosion casts of it with a scanning electron microscope. The Langerhans islets were sporadically situated in the exocrine tissue and were surrounded by the fibrous capsule, which was so tough that it could not be chemically digested easily. This capsule was considered to play different roles in the collection of the endocrine cells in a functional unit, in the prevention of secreted hormones spreading into the adjacent exocrine and stromal tissue, in the support of the microvascular structure, and in the protection for the islet cells from the pancreatic enzymes, which are leaking into the stromal spaces physiologically. The microvascular structure of the islet, disclosed by the corrosion vascular casts, showed afferent vessels branching into the capillaries at the periphery of the islet and entering the core of it by a twisted course. These findings were considered to be related to the islet cell distribution, that is, A and D cells are at the periphery of the islet and B cells at the center of it. This might support the existence of a hormonal regulating mechanism among endocrine cells. In addition, the efferent vessels from the islet that communicate to the vascular network of the exocrine tissue might suggest that the endocrine system also regulates the exocrine function in a circulatory dynamic state.