[Electron microscopic study of mesothelial cells in the diaphragm peritoneum of human fetus using the freeze-fracture replica method].

Electron microscopy of mesothelial cells from the diaphragm peritoneum of human fetuses was conducted using the freeze-fracture replica method. The results were as follows: 1) Numerous vesicles were found in single or cluster forms. The latter type was often fused with large vacuoles and opened to the free surface of the cell as secretory granules. 2) On the fractured faces of plasma and nuclear membranes, different numbers of intramembraneous particles and exocytic pores were seen on the PF surface of the plasma membrane. The diameter of the exocytic pores averaged 43 nm, and their maximum number was 26/microns2. 3) Neighboring cells were conjoined by cytoplasmic processes which were seemed to form three-dimensional intertwinings. 4) The microvilli of the mesothelial cells were grouped into three morphological classes, i.e. fork-like microvilli, bulbous ending microvilli, and stick-like microvilli. In addition, the contrast between the present investigation and the results of fine section studies on the diaphragm peritoneum of human fetus is discussed.