OBJECTIVE: To determine the ultrastructure, relative density, and location of lamellar bodies in the various regions, structures, cells, and intercellular matrix in normal human peritoneum; to carry out engineering analysis of the role of lamellar structures in serosal lubricancy and deduce what effect this system may have on the process of peritoneal dialysis. DESIGN: Five samples of normal human parietal peritoneum obtained at elective operation were fixed in a tannic acid-glutaraldehyde mixture and submitted to examination by transmission electron microscopy. Detailed analysis using reconstruction of serial electron micrographs and tracings of montages were employed in determining location, and disposition, density, and geometric patterns of lamellar bodies in all levels of the peritoneal membrane. RESULTS: Lamellar profiles were found in greatest density enmeshed in surface microvilli and in mesothelial cytoplasm. Lamellar bodies were frequently observed capping the external portion of mesothelial junctional complexes, and within intercellular junctions. Lamellar bodies were also encountered in macrophages, both in the peritoneal cavity and submesothelial tissue, and also in fibroblasts. Lamellar bodies were present in low density in the matrix ground substance of submesothelial connective tissue, in blood vessel walls between smooth muscle, in endothelial cell cytoplasm, and in vascular lumina. CONCLUSIONS: Three-dimensional analysis of lamellae on mesothelial surfaces indicates that an arrangement of constantly changing microscopic spheres and cylinders would act at "ball and roller bearings" among the microvilli for the lubrication of opposing surfaces. The entrapment of fluid in lamellar bubbles, which in normal peritoneum fill the microvillous layer, would, if maintained in peritoneal dialysis, constitute a stagnant layer of considerable stability and inertia.

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