ARCHITECTURE OF THYROID GLAND - A 3-DIMENSIONAL INVESTIGATION

The three‐dimensional structure of the thyroid gland was investigated by reconstructing three‐dimensional models from serial sections of the rat thyroid, stained with the periodic acid‐Schiff technique to identify the basement membrane. It was found that the follicles were not completely separated from each other by connective tissue, reticular fibers, or basement membranes. At some points, the base of the epithelium of a follicle was in direct contact with the base of the epithelium of an adjacent follicle. An area of contact involved about a dozen follicular cells in each follicle. One follicle usually had two or more areas of epithelial contact. All follicles examined in three dimensions (over 100), showed epithelial contacts, in one‐year‐old as well as in younger rats. The area of contact between parenchyma and stroma, as marked by the basement membrane, consisted of a branching system of anastomosed and partially pinched sacs, within which the epithelia of the follicles were in direct contact. Thus, each follicle can no longer be considered as being completely surrounded by connective tissue or even wrapped by a basement membrane discrete from those of neighbour follicles, and therefore its individuality is essentially due to the fact that it owns a discrete lumen. Copyright © 1968 Wiley‐Liss, Inc.