The body cavity is divided into thoracic, cardiac, and abdominal compartments.
In vertebrates, including humans, all vital organs are located within the body cavity, which is surrounded and protected by a body wall made up of ribs, vertebrae, and layers of thick muscle.
The rib cage is constructed as a vertical cone-shaped pouch, with the diaphragm as the moving part at the lower and wider end for the best protection and function of the lung.
Within the limited space of the protected cavity, the lung is constantly moving and changing volume.
The pleura is a serous membrane lined by mesothelium (simple squamous epithelium) that is present as a closed sac that encapsulates the lungs and chest cavity, as a lining.
Structure and function of the pleura
The pleura, pericardium, and peritoneum are membranes that encapsulate the main organs of the body.
The pleura encapsulates the lungs, the pericardium to the heart and the peritoneum to the digestive organs.
The lungs and the chest cavity enlarge and contract in unison during breathing because the lungs are attached to the chest wall by suction.
The pleural cavity, pericardial cavity, mediastinum, and thoracic cavity create the four compartments of the chest.
The lungs are housed within the pleural cavity while the heart is housed within the pericardial cavity.
The pleural cavity is a potential closed space between the parietal and visceral layers of the pleura. It normally contains only a thin film of serous fluid that is secreted from the pleura.
The pleurae are membranes of the thoracic cavity. The pleura represents the serous membrane that lines the lungs.
It consists of two layers, called pleural layers:
The parietal pleura
The parietal pleura, lining the inner surface of the thoracic cavity and rib cage, lies outside the lungs and separates them from the thoracic wall.
The surface of the thoracic walls, thoracic diaphragm, and mediastinum are lined with parietal pleura.
The boundary of the mediastinum is created by the continuation of the parietal pleura, as well as by the space between the lungs.
Aligns the corresponding half of the chest wall separated by the endothoracic fascia (areolar tissue).
It develops from the somatopleuric layer of the mesoderm.
It is innervated by the somatic nervous system and is therefore sensitive to pain.
The parietal pleura has several subdivisions and receives different names that correspond to the structures with which it is associated.
- Cervical: dome-shaped pleura extending towards the neck (the top is 2.5 cm above the clavicle).
- Costal: align the ribs and intercostal spaces.
- Diaphragmatic: pleura that covers the diaphragm.
- Mediastinal: pleura that covers the mediastinum.
- The pulmonary ligament: it is the narrow fold of the parietal pleura that extends below the root of the lung. The functions of the pulmonary ligament are to allow the lung root structures to descend during inspiration and to provide a dead space in which the pulmonary vein can expand during increased venous return (eg, during exercise).
The visceral pleura
The visceral pleura, It is the inner layer of the two layers of pleura.
It is closely adhered to the inner surface of the lung and is aligned with them, it also protrudes in each of the lobar fissures of the lung covering them.
It does not cover the hilum of the lung and the area along which the pulmonary ligament attaches. It develops from the splenic layer of the mesoderm.
It is innervated by the autonomic nervous system and is therefore insensitive to pain. It is continuous with the parietal layer at the root of the lung.
Pleural recesses are the anterior and inferior regions of the pleural cavities that are not normally occupied by the lungs.
In these regions, the two layers of parietal pleura oppose each other resulting in the presence of potential spaces called pleural recesses.
These holes allow the expansion of the lungs during inspiration.
The two recesses of the pleura are:
It is the largest and most clinically important recess.
It is present between the costal and diaphragmatic parts of the parietal pleura.
It is located between the lower edges of the lungs and the lower edge of the pleural cavities and is shaped like the tetra “C”.
It is the most dependent part of the pleural cavity, and therefore fluid from pleural effusions accumulates here first.
It is present anteriorly between the costal and mediatinal pleura.
The left costomediastinal recess is larger due to the presence of a cardiac notch along the anterior border of the left lung.
The serous membrane of the pleura has an approximately equal surface area.
Each is composed of layers of mesothelial cells, basement membrane, connective tissue, microvessels, and lymphatics. Mesothelial cells are a single, pleomorphic layer.
It is made up of superficial microvilli, denser on the visceral side of the pleura.
Stomata are also present in the pleura. Which are openings between cells.
The stoma is found only on the lower anterior chest wall and diaphragm, and is like a drain.
These function as the usual outlets in the lymphatic lagoons for fluids, proteins, and cells.
The pleural cavity, a potential closed space that is little more than a cleft, is placed between the visceral and parietal pleura.
It normally contains only a thin film of serous fluid that is secreted from the pleura.
The space becomes apparent if there is accumulation of air (pneumothorax), blood ( hemothorax ), or pus (empyema).
The mediastinum is responsible for providing protection for the esophagus, thoracic duct, segments of the respiratory tract, major vessels, and some nerves.
This type of compartment helps protect the visceral organs within the various cavities from damage.
Infections are generally unable to travel from one compartment to another, wounds can close one section and leave the other three fully functional, and organ damage is usually limited to a single organ.
Pleurisy, a serious infection of the pleura, will typically only affect one side of the cavity, whereas a knife wound can close only one of the affected segment.
The two sheets that delimit the virtual cavity, the pleural cavity, which does not communicate with the outside or with other organs.
Inside the pleural cavity, a negative pressure forms that allows the lungs to expand during inhalation.
The pleura secretes a fluid that fills the pleural space between the lungs and the rib cage allowing the internal organs to move easily towards each other and reducing the friction created by the movement of the lungs during inhalation and exhalation.
This serous membrane that covers the lungs, divided into two pleural layers that form it are in continuous contact with each other: to ensure and facilitate the sliding of the lungs.
The pleural layers have a thin film of pleural fluid found in the space between the two layers, the presence of which is essential to allow the lungs to follow the movements of the muscles to which they subscribe during respiration.
The pleural fluid between the pleural layers in addition to being essential to prevent separation of the two layers and lubricate the surface of the organs, it also provides surface tension to keep the lungs close to the chest wall.
Therefore, the pleurae allow the volume of the lungs to change along with the volume of the chest cavity and facilitate ventilation.
The pericardium is a sac of dense tissue that surrounds the heart. This membrane secretes fluid into the pericardial space between the heart and the pericardium.
This fluid reduces the friction created by the movement of the heart during the pumping of blood. The peritoneum also consists of two types: the parietal peritoneum and the visceral peritoneum.
The parietal peritoneum lines all the internal walls of the abdominal cavity and the pelvic cavity. The visceral peritoneum covers all the digestive organs.
The peritoneal fluid helps lubricate the internal organs in the cavities, while the visceral peritoneum helps support the organs.
The lung and heart, the vital organs, must be protected and must also move and change the volume continuously to function.
For the best protection and function of the lung, the thorax is almost bag-shaped and the diaphragm is the moving part.
In addition, the outer surface of the lung and the inner surface of the protective rib cage are covered by a lubricating, serous, elastic membrane to form the pleural cavity.
This is almost like inserting a wet, sealed plastic bag between the lung and the chest wall and the diaphragm to decrease friction.
Lubrication is carried out by opposing mesothelial cells that have bushy-surface microvilli that mesh with hyaluronic acid-rich glycoproteins.
The amount of fluid in the pleural cavity is regulated by the hydrostatic-osmotic pressure relationship and pleuro-lymphatic drainage.
Excess fluid, large particles, and cells in the pleural cavity are removed through preformed stomata assisted by respiratory movements.
Finally, clinical and subclinical lesions of the pleura appear to occur often.
Reactive mesothelial cells constantly repair damage and keep the pleural cavity open. Without mesothelial cells, the lung cannot function properly and fibrosis will quickly destroy the pleural cavity.
The pleural ligament refers to the reflection of the layers of the pleura that extend downward. These are found at the root of each lung.
The main responsibility of the pleural ligaments is to provide support for the lungs.
The lungs are basically attached to the chest wall thanks to the way the moist membranes of the visceral and parietal pleura come together.
The interpleural space, also known as the pleural cavity, which is placed between these two membranes is nothing more than a thin layer of fluid that is produced by the membranes.
This creates a suction, similar to two wet glass pieces meeting against each other. The pleural cavity does not really exist in a healthy body.
For the cavity to develop, the body must die or there must be significant disease attacking the area. The neurovascular supply differs for both layers of the pleura.
Innervation of the parietal pleura is provided through the intercostal nerves (innervate the costal and cervical pleura), making it sensitive to pain, pressure, and temperature.
The parietal pleura receives blood supply from the intercostal arteries.
On the other hand, the visceral pleura has an autonomous innervation of the pulmonary plexus (network of nerves that extends from the sympathetic trunk and the vagus nerve), which makes it not sensitive to pain or temperature.
The visceral pleura receives blood supply from the internal thoracic arteries (bronchial circulation), supplied by the systemic bronchial vessels, drains through rather large capillaries into the pulmonary veins and supplies the parenchyma of the lungs.
The upper part of the pleura is called the pleural parietal dome: it is positioned exactly in the supraclavicular fossa and corresponds to the apex of the lung.
From the histological point of view, the pleura is considered as a mesothelium, that is, a tissue that preserves typical characteristics of both the endothelium (the fine tissue that internally delimits the lumen in the blood or lymphatic vessels) and the epithelium (the tissues covering the external surface or lining the internal cavities of the body) and thus histologically resembles one or both.
Mechanisms of pleural fluid accumulation
- Increased hydrostatic pressure, especially systemic venous pressure combined with capillary wedge pressure in congestive heart failure.
- Decreased oncotic pressure: in itself it is not a big problem due to lymphatic reserves.
- Decreased (more negative) pleural pressure from a collapsed lung.
- Increased permeability of the micro vasculature, formation of inflammatory fluid.
- Impaired lymphatic drainage: channel blockage with tumor, fibrosis, among others.
- Peritoneal space fluid, ascites moves through diaphragmatic lymphatics or diaphragmatic defects.
- Gas absorption: depends on the N2 gradient. In pneumothorax, 02 therapy increases the N2 gradient from the pleural space to the venous blood.
Pleural diseases represent a variety of lung-related disorders that affect the general health and function of the lungs.
Pleural diseases do not affect the lungs directly, but rather damage the pleura, which is the lining of the lungs.
When the pleura is damaged, they impair the function of the lung.
There are several different types of pleural diseases that are caused by a variety of underlying elements and conditions. These include:
- Pneumothorax is a condition characterized by air leaking from the lung into the chest cavity (pleural space). This release of air inflates the lung and can ultimately lead to lung collapse.
- Pleural effusion is the most common pleural disease. It is a condition characterized by an abnormal accumulation of fluid in the pleural cavity. This usually occurs when the pleural lining has been exposed to external chemicals or by another disease that causes the lining to heal. This scarring and blockage creates a reservoir of fluid between the chest wall and the lungs.
- Pleurisy is a disease caused by a viral infection or a disease such as pneumonia. It is a condition in which the pleura becomes inflamed. This can cause sharp chest pains, irregular breathing, and coughing.
- Pleural mesothelioma is cancer of the pleura that is caused directly by exposure to asbestos. This cancer accounts for the majority of all cases of malignant mesothelioma.
There are a variety of symptoms that can be the result of a disease related to the pleura.
In most cases, sharp chest pains, cough, fatigue, shortness of breath, and difficulty catching your breath will be evident in almost all conditions.
Treatment for pleural disease will depend on the underlying cause, the disease being diagnosed, the stage of the disease, and the patient’s medical history.
Medications for the lung and heart, surgery, and other more progressive treatments, such as chemotherapy and radiation, are available to treat conditions related to the pleura.