Visceral pleural layer
Visceral pleura (pleura visceralis) is the inner layer of the serous membrane that directly covers the lung itself.
The main feature of this layer is that it fuses extremely tightly with the surface of the lung tissue. Separating it surgically or on an anatomical specimen without damaging the lung itself is practically impossible. Furthermore, the visceral pleura not only covers the lung externally but also extends deeply into the interlobar fissures, completely lining the surfaces of the lung lobes facing each other.
Parietal layer and its parts
Parietal pleura (pleura parietalis) is the outer layer that lines the inner walls of the thoracic cavity. Depending on which thoracic structure this layer is adjacent to, the parietal pleura is topographically divided into four parts:
- Pleura costalis (costal pleura) — adjacent to the inner surface of the ribs and intercostal spaces.
- Pleura diaphragmatica (diaphragmatic pleura) — covers the upper surface of the diaphragm.
- Pleura mediastinalis (mediastinal pleura) — bounds the mediastinum laterally.
- Cupula pleurae (cervical pleura / cupula of pleura) — the upper part of the parietal layer that projects above the superior thoracic aperture.
Pleural cavity
Between the inner (visceral) and outer (parietal) layers, a closed slit-like space is formed, called the pleural cavity (cavitas pleuralis).
Normally, this cavity contains no air and is filled only with a small amount of serous fluid. This fluid acts as a lubricant: it reduces friction between the layers during respiratory movements (inspiration and expiration) and ensures tight adhesion of the surfaces due to surface tension forces.
Pleural sinuses
In areas where one part of the parietal pleura transitions into another (e.g., costal into diaphragmatic), recesses of the pleural cavity are formed — pleural recesses (recessus pleurales). They serve as reserve spaces that the lungs enter only during maximum deep inspiration.
The main recesses are:
- Recessus costodiaphragmaticus (costodiaphragmatic recess) — formed at the junction of the costal and diaphragmatic pleura. It is the deepest pocket of the pleural cavity.
- Recessus costomediastinalis (costomediastinal recess) — located at the transition of the costal pleura into the mediastinal pleura.
Anterior border of the parietal pleura
The topography of the anterior border of the parietal layer is of great clinical importance and differs on the right and left sides.
The course of the anterior border can be described by the following landmarks:
- Begins superiorly at the level of the sternoclavicular joint.
- Runs downwards, passing along the edge of the sternum.
- On the right, the border goes straight down and reaches the level of the 6th rib.
- On the left, the border does not descend strictly vertically: at the level of the lower rib cartilages, it makes a noticeable bend and deviates laterally. This asymmetry is due to the position of the heart, which displaces the left pleural sac.
Briefly: answers to topical questions
What pleural recesses exist?
- Costodiaphragmatic recess (recessus costodiaphragmaticus) — the largest and deepest recess, located in a semicircle from the 6th rib cartilage to the spine, where posteriorly it descends below the 12th rib.
- Mediastinodiaphragmatic recess (recessus mediastinodiaphragmaticus) — formed at the transition of the mediastinal pleura into the diaphragmatic, significantly smaller than the costodiaphragmatic one.
- Anterior costomediastinal recess (recessus costomediastinalis anterior) — formed at the transition of the costal pleura into the mediastinal anteriorly, more pronounced on the left due to the cardiac notch of the lung.
- Posterior costomediastinal recess (recessus costomediastinalis posterior) — formed at the transition of the costal pleura into the mediastinal posteriorly.
At the level of which ribs does the inferior border of the parietal pleura run along the main topographical lines?
- Midclavicular line (linea medioclavicularis) — 7th rib.
- Midaxillary line (linea axillaris media) — 10th rib.
- Scapular line (linea scapularis) — 11th rib.
- Paravertebral line (linea paravertebralis) — 12th rib.
How does the posterior border of the parietal pleura run?
The posterior border of the parietal pleura corresponds to the costovertebral joints.
Which nerves innervate the parietal and visceral pleura?
Afferent fibers from the visceral pleura travel within the vagus nerve, while those from the parietal pleura travel within the intercostal nerves and the phrenic nerve (n. phrenicus).
At what level is the cupula of the pleura located relative to the clavicle and the first rib?
The cupula of the pleura (cupula pleurae) projects above the clavicle into the neck region by 2–3 cm, which corresponds to 3–4 cm above the 1st rib, and posteriorly corresponds to the level of the spinous process of the 7th cervical vertebra.
To easily remember the parts of the parietal pleura, imagine the thoracic cavity as a room: the cupula (cupula pleurae) is the ceiling, the costal part (pleura costalis) is the outer walls, the diaphragmatic part (pleura diaphragmatica) is the floor, and the mediastinal part (pleura mediastinalis) is the inner partition wall.
Class and exam questions
What is the main anatomical difference between the visceral and parietal pleura?
The visceral pleura is tightly fused to the lung tissue and extends into its interlobar fissures, whereas the parietal pleura lines the walls of the thoracic cavity and easily separates from them.
What is inside the cavitas pleuralis?
Normally, only a small amount of serous fluid is present in the pleural cavity, which is necessary to reduce friction between the layers during breathing.
Which pleural recess is the deepest, and why is this clinically important?
The deepest recess is the costodiaphragmatic recess (recessus costodiaphragmaticus). Pathological fluid (blood, exudate) accumulates here first in diseases or injuries.
Why is the anterior border of the left pleura asymmetrical compared to the right?
On the left, the anterior border of the parietal pleura deviates laterally, making way for the heart, which is shifted to the left side of the thoracic cavity.
What else to study on this topic
- Detailed projection of the pleural cupula relative to the clavicle and 1st rib
- Topography and borders of the costomediastinal recess on the skeleton
- Course of the posterior and inferior borders of the parietal pleura
- Anatomical relationships of the visceral pleura at the root of the lung
- Clinical significance of pleural recesses in thoracentesis
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