The ultrastructural morphology and possible functional significance of mesothelial microvilli

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Abstract
The serosal surfaces of major organs and tissues of the body cavities have been examined by scanning electron microscopy following fixation and critical point drying. The micrographs show that these surfaces are covered with microvilli and that the population is most dense on tissues that move about most actively in the body cavities. Radiating from the sides of the microvilli are many fine strands (150 Å, average diameter) which interconnect with each other and adjacent microvilli. Transmission electron microscopic studies of material treated with thorium dioxide at low pH or stained with ruthenium red, reveal these strands to be (1) polyanionic in nature and (2) to arise from a surface glycocalyx which coats the microvilli and intervillar surfaces. It is proposed that the serosal microvilli, together with their glycocalyx, harbor a layer of serious exudate and thereby create a slippery cushion designed to protect the thin mesothelium from frictional damage.