Pleura Definition

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. 


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 (Frequently Asked Questions)

1. What is the Nature of Respiratory Organs in Some Lower Invertebrates?

Answer: Invertebrates are the organisms in which the vertebral column is absent. Through the course of evolution, these organisms came first and then from them the vertebrates were developed. So a very simple type of respiratory system is present in the lower classes and as soon as we go upward in the chart of evolution, the system starts to become more complex. In the coelenterates, the gaseous exchange takes place from the surface of the cells. This is because, in these organisms, the cells are in direct contact with the environment. The respiratory system is absent in some of the lower organisms and in such cases transport of gases is feasible with the help of blood. By the process of diffusion, this oxygen and other gases are passed from one place to another. The moist cuticle of the earthworms is used as a respiratory organ by them. Their body is covered with cuticles and this can be used as a method to exchange gases. It is thin, moist, and vascular in nature and thus it becomes easy for the transport of gases to take place from here. The cockroaches have a network of tracheal systems that is just a network of tubes. Spiracles are some small openings that are present in them and these are the spaces from which the oxygen enters the body of insects and then flows through them. Also by this same mechanism, carbon dioxide is carried out from the body also. 

2. What are Occupational Respiratory Disorders?

Answer: These are the disorders that are related to the respiratory system and the cause of these disorders is working in factories under stressful conditions. They are caused when gases, fumes, and dust are exposed continuously to them. Some common names of the diseases that are caused are Silicosis and Asbestosis. They are caused by continuous exposure to dust at the workplace. The upper part of the lungs is damaged and the fibrosis of the upper part of the lungs occurs. The redness and swellings of the lungs take place. To avoid this, the workers should wear masks, and also long exposures to such conditions should be avoided.