Why Understanding the Pleura Matters in Biology
The human respiratory system is responsible for the process of respiration in human beings. The main organs of the respiratory system are the pair of lungs. The structures that are involved in the respiratory passage are the External nostril, nasal chambers, internal nares, nasopharynx, larynx, trachea, bronchi and bronchioles, and then alveoli at the last. The pleura is the name given to the covering that is present in the lungs. They have visceral and parietal pleura. This is the name given to the inner layer and external layer of the pleura. We will learn more about what is pleura, pleural membrane and pleura membrane.
Lungs
There are a pair of lungs present in human beings. They are present in the thoracic cavity and it is an air-tight chamber. The thoracic cavity is also known as the chest cavity. This cavity is present on the dorsal side of the vertebral column, and on the ventral side, the sternum is present. Ribs are present on the lateral side of the lungs. Below the lungs, the diaphragm is present. This is a dome-shaped structure and it is made up of muscles. This is also responsible for separating the thoracic cavity and abdominal cavity. Pleura and pleural membrane are the two membranes that help in enclosing the lungs. With the thoracic cavity, the outer pleural membrane is in very close contact. And with the lung’s surface, the inner pleural membrane is in close contact. Pleural fluid is the fluid that is present in the fluid cavity. This fluid is secreted by the pleural membrane. The inner layer is called the visceral pleura and parietal pleura is the outermost layer. This helps us to understand what is pleura.
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The Function of Pleural Fluid
As we read above about the pleura, pleural membrane and pleural fluid, now we will learn about the function of the pleural fluid. This fluid helps in lubricating the pleural membranes. This is because at the time of breathing these membranes may slide over each other and if friction is present then it will result in problems of the pleural membrane. So this fluid helps in reducing the friction. Any damage to the lungs or to the pleural membrane then it will affect the process of breathing.
Structure of Lungs
After reading about what is pleura, now we will learn about the pleura anatomy and the structure of the lungs. At the time of birth, the lungs are pink in color. As we grow the lungs are covered with carbonaceous materials and due to this, they become dark grey and mottled. They become darker in color when they are exposed to smoking in adults and also when they are exposed to pollutants. Due to the raised position of the diaphragm, the right lung is smaller than the left lung and this is also due to the presence of the liver. Oblique fissure divides the left lung into two lobes and the right lung also has two fissures that are horizontal and oblique in nature.
Steps Involved in Respiration
As we know, in human beings there are a lot of complex processes that take place in the process of respiration and breathing.
There are Five Steps That are Involved in Respiration.
Breathing: Breathing is a simple process that involves taking in oxygen and then throwing out the carbon dioxide to the environment. Pulmonary ventilation is the other name for breathing.
Diffusion of Gases: After breathing, the gases are then diffused between the alveoli and the blood. Oxygen and carbon dioxide are exchanged across the alveolar membrane. This membrane is very thin and thus this helps in the exchange of gases.
Transport of Gases: The gases are transported with the help of blood.
Diffusion of Gases Between Blood and Tissues: The oxygen is diffused into the blood and the carbon dioxide is diffused from the tissues to the blood.
Utilisation of Oxygen: The oxygen is then utilized by the cells and parts of the body.
FAQs on Pleura: Anatomy, Functions & Relevance
1. What is the pleura and where is it located in the human body?
The pleura is a thin, double-layered serous membrane that plays a crucial role in the respiratory system. It is located within the thoracic cavity. One layer, the visceral pleura, directly covers the surface of the lungs, while the other layer, the parietal pleura, lines the inner surface of the chest wall, the diaphragm, and the mediastinum.
2. What is the difference between the visceral and parietal pleura?
The primary differences between the visceral and parietal pleura relate to their location, nerve supply, and function.
- Location: The visceral pleura is the inner layer that adheres directly to the lung tissue, following all its contours. The parietal pleura is the outer layer that lines the thoracic cavity.
- Sensation: The parietal pleura is highly sensitive to pain, temperature, and pressure, whereas the visceral pleura has no pain receptors and is insensitive to pain.
- Blood Supply: The parietal pleura receives blood from the intercostal arteries, while the visceral pleura is supplied by the bronchial arteries.
3. What is the primary function of the pleura and the pleural fluid?
The main function of the pleura is to allow the lungs to move smoothly and without friction against the chest wall during breathing. This is achieved by the pleural fluid, a thin layer of serous fluid located in the pleural cavity (the space between the two layers). The fluid acts as a lubricant, reducing friction. Additionally, the surface tension of the pleural fluid helps to keep the lungs adhered to the chest wall, facilitating lung expansion during inhalation.
4. What are the different parts of the parietal pleura?
The parietal pleura is a continuous layer but is named according to the structures it covers. Its four main parts are:
- Costal Pleura: Lines the inner surface of the ribs and the intercostal muscles.
- Diaphragmatic Pleura: Covers the superior surface of the diaphragm.
- Mediastinal Pleura: Lines the lateral aspect of the mediastinum, which contains the heart, great vessels, and oesophagus.
- Cervical Pleura: Forms a dome-like structure that extends into the root of the neck, covering the apex of the lung.
5. How does the negative pressure within the pleural cavity facilitate breathing?
The pleural cavity maintains a pressure that is slightly lower than both atmospheric pressure and the pressure inside the lungs. This is known as negative intrapleural pressure. This negative pressure acts like a suction, effectively coupling the lungs to the chest wall. When the diaphragm and intercostal muscles contract to expand the thoracic cavity during inhalation, this suction pulls the lungs outward, causing them to expand and draw in air. Without this negative pressure, the lungs' natural elastic recoil would cause them to collapse.
6. What is pleurisy and how does it cause pain during breathing?
Pleurisy is the inflammation of the pleural membranes. In a healthy state, the two layers of the pleura glide smoothly over each other, lubricated by pleural fluid. When they become inflamed, their surfaces become rough. This causes the layers to rub against each other during respiratory movements, generating friction. Since the parietal pleura is rich in pain-sensing nerve endings, this friction results in sharp, stabbing chest pain that worsens with deep breathing, coughing, or sneezing.
7. What would happen if air entered the pleural cavity?
If air enters the pleural cavity, a condition known as a pneumothorax occurs. The introduction of air disrupts the crucial negative pressure that keeps the lungs expanded. As the intrapleural pressure equalises with the atmospheric pressure, the suction effect is lost. This breaks the adhesion between the lung and the chest wall, and the natural elastic recoil of the lung tissue causes it to pull inward and collapse, either partially or completely. This can lead to sudden chest pain and shortness of breath.
