3.2. Pleural Reflections
The term 'reflection' simply refers to the pleura extending to specific parts of the thoracic cavity; it's another term for the boundaries of the pleura. There are specific reflections for both the parietal and visceral pleural layers.
Key fact: the parietal pleural layer extends further than the visceral pleural layer.
The reflections of the pleurae are not fully symmetrical due to the asymmetrical nature of the thoracic cavity and diaphragm. For example, as the pleural layers descend at the most anterior anterior aspect of the lungs on the left side, they deviate laterally at the fourth costal cartilage to accomdoate the cardiac notch. Take a look at the reflections in the accompanying diagram.
The Visceral Pleural is Shorter
Why is the visceral pleura shorter? 'Viscera' means organs. In this case, it means the lungs. The visceral pleura is adhered to the surface of the lung, while the parietal pleura is adhered to the rib cage. The lungs do not fully occupy the ribcage at all times - if they did, the lungs could not inflate very easily. This means that there is a cavity between the pleural layers, allowing room for the lungs to expand. This cavity is wide in some parts but narrow in other parts of the thoracic cavity. In Sections 3.7. and 3.8., we will see how changes in the volume and pressure of the pleural cavity are linked to muscle movements and are essential for inspiration and expiration.