How does the respiratory system prevent the entry of pathogens?

The respiratory system prevents the entry of pathogens through physical barriers, mucus production, and the action of cilia.

The respiratory system is designed with several mechanisms to prevent the entry of pathogens, which are harmful microorganisms such as bacteria, viruses, and fungi. The first line of defence is the physical barriers. The nostrils and nasal hairs trap larger particles, including many pathogens, preventing them from entering the respiratory system. The nasal cavity and trachea are lined with a mucous membrane that produces mucus, a sticky substance that can trap smaller particles and pathogens.

The mucus in the respiratory system serves a dual purpose. Not only does it trap pathogens, but it also contains antimicrobial enzymes that can kill or inhibit the growth of these microorganisms. One of these enzymes is lysozyme, which can break down the cell walls of bacteria, causing them to burst and die. This is an example of the body's innate immune response, which is non-specific and acts against all pathogens.

In addition to mucus, the respiratory system also utilises cilia, which are tiny hair-like structures that line the respiratory tract. The cilia beat in a coordinated fashion, moving the mucus and trapped particles upwards towards the throat. This is known as the mucociliary escalator. Once the mucus reaches the throat, it can be swallowed and the pathogens are destroyed by the acidic environment in the stomach.

Furthermore, the respiratory system has a reflex mechanism known as the cough reflex. When the respiratory tract is irritated, for example by the presence of pathogens or foreign particles, a signal is sent to the brain to trigger a cough. This forceful expulsion of air from the lungs helps to clear the respiratory tract of the irritants.

In summary, the respiratory system employs a combination of physical barriers, mucus production, the action of cilia, and reflex mechanisms to prevent the entry and spread of pathogens.