The pleura is a membrane that surrounds the lung and consists of two membranes, the parietal and the visceral, which are continuous in the hilum region of the lung. The parietal and visceral membranes delimit, for each lung, an independent cavity fully lined by the mesothelium. Typically, this pleural cavity is virtual, containing only a thin layer of lubricating fluid (pleural fluid), allowing smooth sliding of these two membranes during respiration, preventing friction between the visceral and parietal mesothelium.
The visceral and parietal pleural membranes are usually held together due to decreased pressure in the pleural cavity.
Metrology is the scientific study of measurement. .The first being the definition of units of measurement, second the realisation of these units of measurement in practice, and last traceability, which is linking measurements made in practice to the reference standards.
