The lungs are one of the most important organs in the body! Not only do we need our lungs to carry out the exchange of oxygen and carbon dioxide, but they are also an important blood-forming organ.
Structure of respiratory system
The lungs are connected to the nose and mouth, and the entire passageway makes up the respiratory system. Among them, according to the respiratory tract structure characteristic, people will whole respiratory tract is divided into the upper respiratory tract and the lower respiratory tract. The upper respiratory tract consists of the nose, pharynx and larynx, while the lower respiratory tract consists of the trachea, bronchus and lungs. What people often says “cold”, medical profession name is called “acute upper respiratory tract infection”, abbreviation is acute on feeling. After invading respiratory tract as a result of the pathogen such as virus, bacteria, it is first attached at the department of nasal throat, and a series of inflammatory reactions caused. The respiratory tract is formed around the epithelium of the respiratory tract, which spreads long cilia into the respiratory tract, and goblet cells, which secrete mucus.
When viruses and bacteria cause infections in respiratory epithelium and other tissues, goblet cells secrete rich mucus to wrap up pathogens, and then swing to the mouth and nose through the cilia of epithelial cells regularly, eventually leading to the expulsion of “sputum” rich in pathogens from the body. Therefore, in general, viruses and other pathogens have little chance to enter the lower respiratory tract directly. However, there are always some special conditions that can lead to the formation of bronchitis and pneumonia.
The physiological role of the lung
A person’s lungs are made up of left and right lungs, with the left having two lobes and the right having three. As oxygen-rich air is sucked in from the mouth and nose, it travels through the trachea and bronchi to reach the five lobes of the lungs. The lungs are rich in capillaries, and oxygen-rich air passes through the trachea and bronchi to reach structures called alveoli. One of the components of the alveoli are the extremely developed capillaries.
The alveoli can contract and relax on their own rhythmically. The alveoli dilate and swell, and oxygen-rich fresh air rushes in; The alveoli contract smaller and carbon dioxe-rich waste gases are expelled. When oxygen-rich fresh air enters the alveoli, the oxygen content in the alveoli is higher than that in the capillary blood, so the partial pressure of oxygen in the alveoli is higher than that in the blood.
As a result, oxygen flows from the alveoli into the blood, where it is eventually carried around the body by hemoglobin. As cells throughout the body metabolize, they inevitably consume oxygen and produce large amounts of carbon dioxide. So as the blood flows through the alveoli, the concentration of carbon dioxide in the blood is naturally much higher than in the alveoli, the capillaries and the pCO2 in the blood is much higher than the pCO2 in the alveoli. As a result, the waste gas carbon dioxide is discharged from the blood into the alveoli, and eventually through the respiratory tract, out of the body.
Formation of pneumonia
As mentioned above, throughout the respiratory tract, there is a rich system of cilia on the surface of the wall cells, which oscillates in a directional way over the nose and mouth. When pathogens such as viruses and bacteria invade the respiratory tract, goblet cells and other cells secrete mucus to stick the viruses and bacteria, and finally discharge them from the body under the action of cilia. However, if the number of viruses and bacteria is huge, it exceeds the self-purification ability of the human body. So, some viruses and other pathogens can go to the alveoli.
Viruses and other pathogens that come to the alveoli naturally need the body’s immune cells to fight them. Macrophages, for example, swallow viruses, bacteria and other foreign bodies into the body, and eventually use a powerful “protein degradation system” to destroy them. In addition, in order to accelerate the response to the foreign threat, T cells, B cells and other will be mobilized. The main purpose of T cells is to destroy pathogens, such as viruses, that might exist in tissue cells.
Although immune cells such as macrophages can kill pathogens directly, they cannot distinguish pathogens lurking within their cells. T cells, on the other hand, rely on specific mediators to distinguish normal cells from infected ones. It then attaches to the surface of the infected cell and eventually initiates the cell’s self-apoptosis process.
The cell then ruptures on its own, exposing pathogens such as viruses. And macrophages and so on can destroy these “cunning” guys. Although the immune system is strong, it doesn’t always win. Pathogens such as viruses “win” when the immune system is weak, such as in children and the elderly, or when tired. They then further proliferate in tissues such as the alveoli.
To combat them, the body starts to run a fever, suppressing the proliferation of the pathogen, and a lot of energy is spent on the proliferation of immune system cells to fight off further attacks by the pathogen. And the inflammation gets worse and worse, and eventually, there’s a lot of fluid in the alveoli, and it takes over the alveoli. As a result, the body starts not getting enough oxygen. Eventually, it can lead to dyspnea, chest pain, headache, coma and, in severe cases, suffocation and death.
Now, novel coronavirus is spreading through the land. What makes the virus so frightening is that it causes a severe inflammatory reaction (pneumonia) in the lungs that can lead to serious conditions such as difficulty breathing and lack of oxygen. Plus, it’s a new virus, and our immune system has never been exposed to it. So when it strikes, the immune system doesn’t respond as quickly as it would with a common virus. This is probably why it travels through the upper respiratory tract and directly to the lungs. Because common viruses in the upper respiratory tract, will be detected by the body’s immune system, and then mobilize immune cells to kill it. Without ending up in the alveoli and causing widespread viral proliferation and infection.
Objectively speaking, any pathogen entering the alveoli to cause pneumonia is very dangerous. For example, tuberculosis caused by the bacterium tuberculosis pneumonia. TB is a bacterium, and we’ve been inventing a series of antibiotics since the beginning of the last century that specifically target bacterial infections. But, even so, if the TB bacterium can reach the alveoli, it can cause pneumonia. We’re going to have to kill it with several antibiotics in a row over the next few weeks, and that’s going to be tough. This may have to do with the abundance of capillaries in the alveoli, because they can quickly reproduce with nutrients. And virus, this extremely “evil” species, we do not have a specific drug to fight against it, a lot of “helpless”.