Formed by thin membrane that forms a double layer of protection
Visceral layer — layer covering the organs
Parietal layer – lines the outer walls
Mesothelium – body cavities are lined by a single layer of flat cells – the mesothelium mesothelial cells
Normally separated by a thin layer of fluid 1- 12 ml
In the absence of disease the fluids within a body cavities are limited to a insignificant lubricating layer that can not be aspirated. Therfore the mere presence of a fluid in any of the body cavities, and especially a quantity of fluid sufficient for tapping, indicates a PATHALOGIC PROCESS.