How do the cells lining bronchus protect alveoli from damage?

The cells lining the bronchus play a crucial role in protecting the delicate alveoli, which are the primary sites of gas exchange in the lungs, from damage and harmful substances. Here are some important mechanisms by which these cells provide protection:

1. Mucociliary Escalator:

- The cells lining the bronchus are covered in a layer of mucus, which acts as a sticky barrier trapping inhaled particles, bacteria, and other foreign materials.

- Cilia, which are tiny hair-like projections present on these cells, beat in a coordinated manner, propelling the mucus layer (along with the trapped particles) towards the throat. This process is known as the mucociliary escalator.

- By efficiently removing foreign materials from the airways, the mucociliary escalator helps prevent them from reaching and potentially damaging the alveoli.

2. Secretory Cells:

- Specialized secretory cells, such as goblet cells and serous cells, are present among the lining cells of the bronchus.

- Goblet cells secrete mucin, a major component of mucus, which contributes to the formation of the protective mucus layer.

- Serous cells secrete a watery fluid that keeps the mucus layer hydrated and facilitates the movement of the mucociliary escalator.

3. Filtration and Absorption:

- The cells lining the bronchus have the ability to filter out and absorb certain particles and chemicals from the inhaled air.

- This helps remove pollutants, allergens, and potentially toxic substances before they can reach the sensitive alveoli.

4. Tight Junctions:

- The cells lining the bronchus are tightly connected to each other through specialized cell junctions called tight junctions.

- These tight junctions create a barrier that prevents the leakage of fluid and harmful substances from the bronchus into the surrounding lung tissue and alveoli.

5. Immune Function:

- The cells lining the bronchus are part of the respiratory immune system and play a role in defending against respiratory infections.

- They secrete antimicrobial substances, such as defensins and lysozyme, which help combat bacterial and viral infections.

- Additionally, these cells can interact with immune cells like macrophages and lymphocytes, facilitating immune responses and maintaining respiratory health.

By performing these protective functions, the cells lining the bronchus contribute to maintaining the integrity and functionality of the alveoli, ensuring efficient gas exchange and overall respiratory health. Damage or dysfunction of these lining cells can impair respiratory function and contribute to the development of various respiratory diseases.