Colonic pericryptal fibroblast sheath: replication, migration, and cytodifferentiation of a mesenchymal cell system in adult tissue. II. Fine structural aspects of normal rabbit and human colon.

Abstract

Summary The colonic pericryptal fibroblast sheath is a self-renewing population of mesenchymal cells which maintains intimate contact with the base of the epithelium as it and the epithelium. migrate synchronously from their germinative zones to the surface of the crypt. The fine structural appearance of the fibroblast changes during the migration from that of an undifferentiated cell at the lower part of the crypt to that of a mature fibrocyte engaged in protein synthesis at the upper part of the crypt. The change in functional appearance is correlated with the appearance of a wide collagen table under the surface epithelium. The shingling of the fibroblasts creates a complete sheath around the lower portion of each crypt. This cellular sheath is fenestrated under the free surface where only delicate, stellate processes of the fibrocytes maintain close contact with the epithelial basal lamina. The fenestrated appearance of the pericryptal fibrocyte processes in the zone of cellular differentiation, which subtends the fully differentiated absorptive epithelium, may shed some light on the nature of the epithelial basal complex and the role of the pericryptal sheath and the collagen table in fluid transport across colonic mucosa. The constant maintenance of intimate fibroblast-epithelial contact throughout the crypt is additional reason to suppose that a well ordered system of epithelial-mesenchymal interaction is involved in normal structure, renewal, and function of colonic mucosa.