What is a membrane consisting of two layers which are kept moist and allow surfaces to slide smoothly over each other during the act of breathing in the respiratory system?

Answer 1

PLEURA

Each lung is enclosed in a serous pleural sac consisting two continuous membrane called visceral and parietal pleura. The two layers are continuous with each other around the hilum of the lung and enclose a potential space between them known as the pleural cavity. The pleura are lined by mesothelium. The visceral pleura invest all the surfaces of the lung forming their shiny outer surface and the parietal pleura lines the pulmonary cavities. The pleural cavity contains a layer of serous pleural fluid, which lubricates the pleural surfaces and allows the layers of pleura to slide smoothly over each other during respiration. Its surface tension also provides the cohesion that keeps the lung surface in contact with the thoracic wall.

The visceral pleura or pulmonary pleura closely covers the lung and is adherent to all its surfaces, including the surfaces within the horizontal and oblique fissures. The visceral pleura dip into the lung fissures so that the lobes of the lung are also covered with it. The visceral pleura are continuous with the parietal pleura at the hilum of the lung.

The parietal pleura line the pulmonary cavities. The parietal pleura consists of four parts

1. Costal pleura- covers the internal surfaces of the thoracic wall.( ribs and intercostals spaces)

2. Mediastinal pleura- covers the lateral aspects of the mediastinum.

3. Diaphragmatic pleura- covers the superior or thoracic surface of the diaphragm on each side of the mediastinum

4. Cervical pleura (pleural cupula or dome of pleura)- extends from the superior thoracic aperture into the root of the neck, forming a cup shaped pleural dome over the apex of the lung.

The pleural cavity is the potential space between the layers of pleura and contains a capillary layer of serous pleural fluid, which lubricates the pleural surfaces and allows the layers of pleura to slide smoothly over each other during respiration.