visceral pleural and parietal pleural

 Both the visceral and the parietal pleura play an important role in fluid homeostasis in the pleural space. A pleural effusion represents a disturbance of this equilibrium, probably because of both increased production and decreased resorption. Low oncotic pressure (e.g., in hypoalbuminemia), elevated pulmonary capillary pressure, increased permeability, lymphatic obstruction, and diminished negative intrapleural pressure are all pathophysiological components that lead to the clinically relevant and distinguishing features of a pleural effusion—transudate vs. exudate. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6647819/#:~:text=The%20most%20common%20causes%20of,the%20further%20diagnostic%20work%2Dup.