The ultrastructure of vesicle-containing cells and ER-cells of human peritoneum.

In 16 human specimens the mesothelial cells of the diaphragmatic peritoneum and the pelvic parietal peritoneum were observed by transmission electron microscopy and freeze fracture replica. There were two types of cells i.e. the vesicle-containing cells and ER-cells. The former were found only in the diaphragmatic peritoneum and contained numerous cytoplasmic vesicles. These vesicles could be alone or in clusters. The clustered vesicles were often fused to form large vacuoles which opened on the free surface of the cell, into the intercellular space, or through the basement membrane, or sometimes became secretory particles on the free surface of the cells. Some vesicles were also observed in the microvilli. The latter were only found in the pelvic parietal peritoneum and contained abundant endoplasmic reticulum. The vesicle-containing cells seemed to absorb the material from the peritoneal cavity. The ER-cells contained abundant endoplasmic reticulum and Golgi apparatus, and showed high synthetic activity, possibly related to the production of peritoneal fluid.