When there is more fluid than normal in the pleural cavity, it is called a pleural effusion. Pleural effusion can occur in both adults and children.

The upper respiratory system includes the nose, pharynx, throat, sinuses, and larynx, which are responsible for taking in air from outside the body, warming it, and filtering it before it enters the lungs. Meanwhile, the trachea, bronchial tree, alveoli, pleura, and lungs of the lower respiratory system are responsible for filtering air and exchanging gases. Therefore, each part has certain functions.