Observations on the Surface Cells of the Mouse Omentum as Studied With the Phase-Contrast and Electron Microscopes

Abstract

The conformation and fine structure of the cells covering the surface of the normal, or control, omentum are described. Some of the observations are of particular interest in the light of past controversies concerning the apposition and potentialities of mesothelial cells. Both macrophages and mesothelial cells compose the surface layer of the milky spots. The mesothelial cells, which are contracted, are in the majority, macrophages being interspersed among them. Openings occur between the cells on the milky spots thus exposing the underlying cells or collagen fibers to the surface. No basement membrane appears beneath any of the cells covering the omentum. The surface cells of the netlike areas of the omentum are flattened, tenuous mesothelial cells that appose each other by adjoining or overlapping. The possible significance of the milky spots and their surface modification in relation to the reticuloendothelial system is discussed. Whether the surface macrophages function as sessile phagocytes or migrate in response to stimulation must be determined by experimental studies. Macrophages and mesothelial cells being close neighbors on the omental surface makes this an advantageous region for comparing their reaction to various stimuli.