Pleural Cavities and Serous Membranes

The pleura is the serous membrane that surrounds each lung, and the pleural cavity is the thin, sealed space it encloses. The visceral pleura adheres to the lung surface and is continuous at the hilum with the parietal pleura, which lines the inner thoracic wall, diaphragm, and mediastinum. Between the two layers lies a small volume of serous fluid that lubricates their movement and couples the lung to the chest wall, so that the lung follows the cage as it expands.

Definition

The pleura is the serous membrane comprising a visceral layer covering the lung and a parietal layer lining the thoracic wall, diaphragm, and mediastinum; the pleural cavity is the potential space between these layers, containing a thin film of lubricating serous fluid.

Scope

This topic covers the two pleural layers and their continuity, the regions and recesses of the parietal pleura, the contents and function of the pleural cavity and its serous fluid, and the mesothelial lining that produces and absorbs that fluid. It is a reference-educational account of normal pleural anatomy and is not clinical guidance.

Core questions

• How are the visceral and parietal pleura arranged and where do they become continuous?
• What are the regions and recesses of the parietal pleura?
• What does the pleural cavity contain and how does its fluid behave?
• How does the pleural lining produce and absorb serous fluid?

Key concepts

• Visceral pleura and parietal pleura
• Pleural cavity as a potential space
• Serous (pleural) fluid
• Costodiaphragmatic and costomediastinal recesses
• Mesothelium
• Pleural reflection lines
• Negative intrapleural pressure

Mechanisms

The two pleural layers are continuous around the hilum, enclosing a closed cavity that normally holds only a thin film of serous fluid. This fluid lubricates the sliding of the visceral over the parietal pleura during breathing and, together with the surface tension between the wetted layers, mechanically couples the lung to the chest wall so that the lung expands and recoils with the cage. The pleural surfaces are lined by mesothelium, whose junctional properties regulate the movement of fluid and solutes that maintains the small, balanced volume in the cavity; fluid is secreted and absorbed continuously rather than being static (Yalcin 2013; Markov 2014; Standring 2020). Where the parietal pleura turns sharply at the costal margins, the lung does not fully fill the cavity, leaving recesses such as the costodiaphragmatic recess into which the lung descends on deep inspiration (Moore 2018).

Clinical relevance

The pleural recesses are dependent regions where fluid tends to collect, and the layered pleural anatomy explains how the lung normally remains apposed to the chest wall and how that apposition can be lost. This entry describes the normal anatomy and physiology of the pleura for orientation; it does not provide diagnostic criteria or treatment advice.

Evidence & guidelines

Pleural layers, recesses, and reflection lines are described in standard reference anatomy (Standring 2020; Moore 2018). The structure and fluid-handling function of the pleura and its mesothelium are reviewed in the thoracic and physiology literature (Yalcin 2013; Markov 2014).

Seminal works

• yalcin-2013
• standring-2020

Frequently asked questions

What is the difference between the visceral and parietal pleura?

The visceral pleura covers the surface of the lung, while the parietal pleura lines the thoracic wall, diaphragm, and mediastinum; the two are continuous at the hilum and enclose the pleural cavity (Standring 2020).

What does the pleural cavity normally contain?

Only a thin film of serous fluid that lubricates the two pleural layers and, with surface tension, couples the lung to the chest wall; it is a potential space rather than an open cavity (Yalcin 2013).